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Janelle Leboutillier

Chapter 12: Predation and Herbivory • Recall: Over half the species on Earth obtain energy by feeding on other organisms, in a variety of types of interactions. • All are exploitation—a relationship in which one organism benefits by feeding on, and thus directly harming, another. Exploitation: an (+/-) interaction in which one organism benefits from feeding on and thus directly harming the other. This can reduce the growth, reproduction, and survival of organisms, decrease densities, and alter distributions. How it chooses what to eat can be very complex? Organisms may choose to eat another organism because it supplies nutrients needed or its just is easy to capture. • Prey Switching Classic Model: A predator will switch prey based on the availability. E1/E2 = c(N1/N2), where E1/E2 is the ratio of prey 1 eaten relative to prey 2 and N1/N2 is the ratio of prey 1 in habitat relative to prey 2. Species 1 and 2 are 2 separate prey species. c - how much does the predator prefer prey 1 over prey 2. • Population Cycles: caused by 3 way interactions between predators, prey, and plants. can be represented mathematically by Lotka-Volterra predator prey model dN/dt = rN - aNP and dP/dt = baNP – mP, where N is the number of prey, P is the number of predators, r is population growth rate, and b is rate that prey are converted to predator offspring. Together, rN is exponential growth, aNP is removal of prey by predators, baNP is exponential growth depending on predators ability to turn prey into births, and mP is the death rate. The capture efficiency, which depends on how frequently predators and prey encounter one another, NP. Prey decreases when P> r/a and increases when P< r/a. Predators decrease when N m/ba This is hard to model experimentally. When P = 0 there is exponential population growth but when P≠0, rate of prey capture depends on NP and a. If N = 0, predator population decreases exponentially by m but when N≠0 individuals are added to the predator population according to aNP and b. The amplitude of cycles depends on the initial amounts of predators and prey and the cycles are asynchronous (predator high while prey is low and vice versa). • Hairston et. al: a rotifer predator and algal prey cycled asynchronously and it was proposed that the rotifer eggs viability increase with prey density, algal nutrition quality increases with nitrogen concentrations, accumulation of toxins alters algal physiology, and the algae evolves in response to predation. These assumptions were tested with mathematical models and prey evolution manipulated by using one genotype only. The lack of evolution allowed for typical population cycling, but with evolution cycling was asynchronous. Resistant algal genotypes were poor competitors (tradeoff), when predators are high, these increase as well but when predators are low, other genotypes out compete them. • Snowshoe Hare Case Study: it was shown that lynx and snowshoe hare population cycles peaked every 10 years, and the rise and fall of the cycle occurs across broad regions of Canadian forest. The hares tend to have consistent birth and death rate and dispersal isn’t significant enough because the geographic range is so large. However experimenting by adding food may not fix the cycle decline. They can raise 3-4 litters per summer with 5 offspring each. Population reaches highest levels just before density reaches a maximum, then reaches a low 2-3 years after it peaks. The birth/death rates of hares change because vegetation (food) becomes limited at high density and due to increased predation at high density, but doesn’t explain why birth rates drop during decline cycling phase, why the population rebounds slowly when predator levels drop, and why the physical condition of the hares after/during predation is poor. An experiment with 1x1km plots of land was used to determine survival rates and densities of hares over 8 years. Results showed lowest densities in the +predator/-food control, then – predators/-food, then +predators/+food, then –predators/+food. The lynx movement from one region to another may be enough to cause synchrony in hare cycles across broad geographic regions. The hare cycle also continued in – predators/+food experiment, meaning flying or climbing predators may have entered the fences, the hares had stress from fear of predation, or a pathogen infected them. Chapter 13: Parasitism • Enslaver Parasite Case Study: Some parasites can alter the behaviour of their host in order to complete their life cycle. hairworms infect hapless crickets when the crickets drink water infected with hairworm larvae. The hairworm feeds on the cricket’s tissues, grows to take up the whole cricket’s body cavity, then controls the cricket’s perception of thirst so it jumps into a body of water and drowns. The hairworm then emerges from the cricket so it can enter the water and mate. New larvae will only survive if ingested by another terrestrial arthropod. It was shown that when crickets were saved after jumping into the water, they would jump back in, unlike uninfected crickets. It is also known that some fungal species control insect behaviour to allow for optimal dispersal of spores when the host dies Ex. flies climb up tree/plant to higher leaves, hook on, die, and spores grow and disperse. Some vertebrates can be enslaved as well Ex. rats with toxoplasma gondii protist infection are attracted to cats, allowing the parasite to spread to cats when eaten, which can spread to humans causing mental disorders and reduced reaction time • The parasitoid wasp Hymenoepimecis argyraphaga manipulates its host, the orb- weaving spider Pleisometa argyra, to spin a special cocoon web • Symbionts: organisms that live in or on other organisms. Many are mutualists, however most are parasitic. Over half of the existing species on Earth are symbionts. • Parasites: an organism that lives in/on another organism (host) and feeds on its tissues and/or body fluids. Parasites don’t usually kill the host immediately, tend to feed on one/few hosts, and have a higher reproductive rate than the host. The degree of harm from parasites ranges from mild to lethal. Some parasites alter the behaviour of their host to complete their life cycle Ex. hairworms in hapless crickets. Herbivores, and parasitoids can also be parasites. Since parasites usually feed on specific hosts, this is the reason why there is high diversity in parasites. About 50% of Earth’s species are parasites. There are different types: o Macroparasites: large parasites such as worms. o Microparasites: small parasites such as fungi, bacteria, protists etc.  Parasite Natural History: Most parasites feed on only one or a few individual host organisms. Defined broadly, parasites include herbivores such as aphids, nematodes, that feed on one or a few host plants. Parasitoids whose larvae feed on a single host, almost always kill it. o Ectoparasites: parasites that live on the outer body surface of its host. This includes plants that grow on and obtain water and food from another plant through modified roots called haustoria. (Dodder). Some plants are hemiparasitic (mistletoes) and can obtain energy through photosynthesis as well. Some insect and animal herbivores live on and eat stems and leaves of certain plants and therefore are herbivores and parasites. Many ectoparasites include fleas, ticks mites (animals) and rusts, smuts, and mildews (plants) Athlete’s foot fungus, lice. Some parasites also transmit disease. Some ectoparasites are pathogens.  Many fungal animal parasites are ectoparasites. More than 5000 species of fungi attack important crop and horticultural plants. Mildews, rust and smuts grow on the surface of the host plant and extend their hyphae (fungal filaments)into the plant to extract nutrients from its tissues  Plants are also attacked by animals, aphids, whiteflies, scale insects, nematodes, beetles and juvenile cicadas. These animals can be thought of as herbivores and parasites (specially if they remain on one plant their entire life). • Endoparasites: parasites that inhabit the host especially alimentary canal (digestive tract) and live within host tissues and cells of animals and plants. (disease organism). Those that live in the alimentary canal eat the food that the host ingests or absorb already digested food instead of feeding on the host’s tissues. This causes nutritional deficiencies. Includes worms, fungi, bacteria etc. Many do not eat the host tissue but rob the host of nutriens. Tapeworm, tuberculosis, soft rot. Ectoparasitism vs Endoparasitism Ectoparasitism Endoparasitism Advantages • Ease of dispersal • Safe from host’s immune system • Ease of feeding • Protected from external environment • Safer from natural enemies Disadvantages • Feeding more difficult • Vulnerable to natural enemies • Exposed to external environment • Dispersal is difficult • Vulnerable to host’s immune system NOTE: some endoparasites overcome the dispersal problem by exiting the host Ex. through fecal matter or by entering complex life stages specialized for dispersal. They also overcome the immune system by developing tolerance. Pathogens: parasites that cause disease. Defenses: parasites and hosts exert selection pressures onto each other. This involves the exoskeleton, immune system, resistance genes, and chemical defense. Ex. the host may develop a stronger immune system to limit the severity of parasite attacks, which causes the parasite to evolve new ways to tolerate the immune system. Immune System: involves specialized cells that allow the host to recognize parasites that it was previously exposed to. It also has cells to engulf and destroy parasites and mark them for later destruction. Plants are able to elicit immune responses also using resistance genes or production of antimicrobial compounds to attack bacterial cell walls or fungus. Plants may also produce chemical signals to warn other cells of the parasite or produce lignin to provide a barrier to prevent spread. Biochemical Defense: can be used by a host to prevent parasite growth. Ex. transferrins are used to remove iron from blood serum, which endoparasitic fungus uses to survive and thus the fungus will not survive unless it finds a way to acquire iron from the host. Some hosts can change their food source to a more toxic one to help fight parasites Ex. woolly bear caterpillar eats poison hemlock or chimpanzees eating bitter plants to kill nematodes. Plants can release secondary compounds to treat infections. Parasitoids: parasites that lay eggs, which hatch into larvae, which feed on a single host and almost always kill it. These are unusual parasites because they kill their host and unusual predators because they only consume one or few hosts in a lifetime. Mate Choice: some organisms will select mates based on whether they have an effective defense system. This can be detected by colour, behaviour, scent, presence of a certain chemical etc. Ex some fish have more MHC proteins, which are important to immune function, which mates can smell. Encapsulation: where a host species covers parasites or parasite eggs with capsules that kill them or make them harmless. Lamellocytes: found in insects, specialized blood cells that form multicellular sheaths (capsules) around large objects. This can destroy all or most of the attacking parasites. Some parasites can overcome this by injecting virus-like particles upon infection to destroy lamellocytes and thus decreasing the host’s resistance. Other parasites lay eggs covered in a substance that prevents detection by lamellocytes. Plasmodium: endoparasites that cause malaria, where they form the sporozoite stage in mosquitoes and the merozoite stage in humans. The merozoite enter RBCs, multiply, University of Toronto Created By: Lindsay Arathoon 33 break out, and cause malaria symptoms. The merozoites can also transform into gamete producing cells, which can be picked up when another mosquito bites, forming more sporozoites in the mosquito for the next human host. The plasmodium has to overcome the fact that RBCs do not import nutrients for growth and the fact that the RBCs become deformed, detected by the spleen, and destroyed along with the contained parasites. Special genes are used to attach proteins to the RBC surface overcome this, and since proteins vary by parasite, it is hard for the immune system to recognize and destroy them. Myxoma Virus: found in Australia and observed in European rabbits when they were introduced to the area. The population increased so much, they became pests and humans introduced predators and used shooting to control the levels. These methods didn’t work, so this mosquito-transmitted virus was introduced, causing skin lesions, swelling, difficulty eating/drinking and death. This killed 99.8% of the rabbits, but the remaining rabbits were resistant, thus mating caused an increase in resistant individuals. As a result the virus evolved into less virulent forms to kill less hosts, remain in the host for longer, and therefore have a better chance for being spread. New virus strains must be produced to keep the rabbit levels under control due to coevolution. Gene-for-Gene Interaction: when a particular genotype is resistant to particular parasite genotypes. If the parasite develops new genotypes, the genotype of the host may no longer be resistant. The changes in genotypes of parasites and hosts occurs naturally. It has been shown that parasites are able to infect hosts of their home region better than hosts of other regions since they had evolved to overcome the defense of hosts in their home region. Common genotypes in hosts are at greater risk than rare genotypes so the parasite can affect more individuals. Arms Race: hosts and parasites impose selection pressures on each other, thus both the parasite and host evolve into stronger and more resistant and effective forms overtime for parasite to overcome host defense and host to improve parasite resistance. However, this arms race doesn’t continue indefinitely due to tradeoffs Ex. an increase in host defense may begin to take away from growth, reproduction, and survival or more virulent fungal pathogens produce less spores or overcome fewer host resistance genes than weaker pathogens. Extinction: in severe cases, parasites can drive a host species to extinction (locally or over a large region). Ex. trematode parasites can drive Corophium amphipod crustaceans to extinction in 4 months with an initial host population density of 18000 individuals per square meter. Ex. Chestnut species are affected by lethal fungal pathogens, and now the trees are isolated to regions of North America. Poulation Cycles: also affected by parasites. Ex. red grouse in England had decreased survival and reproduction due to parasitic nematodes. Hudson et al treated the grouse during 2 years that were predicted to show population crashes due to the parasite, as well as treatment for 1 of the years, and no treatment. It was shown that the treated groups had smaller amplitude population cycling than untreated. Species Interaction: where parasites affect the outcome of species interactions by altering the physical condition or behaviour of their host. Ex. the host elicits behaviour that makes it more vulnerable to predation. Community Structure: since parasites can cause large decreases in population numbers they can change communities and species interactions. Ex. a fungal pathogen University of Toronto Created By: Lindsay Arathoon 34 wiping out an insect herbivore that eats 6 plant species resulted in an increase in the abundance of the species previously being eaten, thus increasing the numbers of other herbivore feeders. Ex. a sexually transmitted mite in beetles decreases the % of successfully hatching eggs. Parasites can also change the physical environment. Competition Outcome: affected by parasites. Ex. If a parasite is introduced and affects one competing species but not the other, it could cause competition reversal. Ex. T castaneum and T confusum beetles were introduced to a pathogen, and the T confusum went from the inferior competitor to the superior one. Ecosystem Engineer: a species whose actions change the physical character of its environment Ex. when a beaver builds a dam or Corophium amphipods burrowing to prevent erosion. Trematodes that infect Corophium means less burrowing, leading to erosion. Disease Spread: for this to occur, the density of susceptible hosts must exceed a critical threshold and there must be presence of a pathogen. The host population includes the susceptible, the infected, and the recovered individuals. The genotype of the pathogen and other factors such as host age, latent periods (where infected individuals are not contagious), and vertical transmission (from mother to newborn) are important to know. Host-Pathogen Dynamics Model: used to measure threshold density and control establishment and spread of diseases. Where S represents susceptible and I is infected individuals. Infected individuals must encounter susceptible ones for disease to spread and the rate that this occurs depends on the densities of each. Therefore the encounter rate is SI and the transmission coefficient is β, making disease transmission βSI. Death and recovery rate is represented by d, therefore dI/dt = βSI – dI, where dI/dt is change in density over time. Density of infected individuals increases when the disease is successfully spread and decreases with death or recovery of infected individuals (d). Disease spreads when dI/dt > 0, (βSI – dI) > 0 or S > d/β = ST. The disease establishes when S exceeds the threshold density, ST=d/β (otherwise the disease contracts). If β is decreased, ST will increase. S values below ST prevent disease spread and this can be achieved with vaccinations, washing hands etc. to reduce spreading. NOTE: small populations under the threshold have a smaller chance of spreading disease however if affected they risk extinction. Climate Change: can contribute to disease spread in humans and other forms of wildlife. Ex. increased ocean temperature is associated with coral and amphibian diseases. It can also change the location of suitable habitat for some organisms. Parasitoid Wasp: infects the orb- weaving spider, where the larval stage attaches to the spider’s abdomen, sucks out the fluids, and forces the spider to make a cocoon web. The spider is then killed and eaten, and the larvae spins a cocoon and attaches it to the cocoon web to develop into a wasp while protected by the web. The change in web that the parasitized spider produces only occurs once the larvae needs to build its cocoon due to the injection of a chemical into the host. Removal of the larvae results in an abnormal, non-cocoon web. Chapter 14: Mutualism and Commensalism Farming Case Study: the first farmers were ants of tropical forests in South America known as attines 50mya. These ants cultivate fungi, which in turn depend on the ants. University of Toronto Created By: Lindsay Arathoon 35 When a virgin queen leaves the nest to start a new colony, it carries fungi with it to start a new subterranean fungal garden the size of footballs to support 2-8 million ants. Some ants may cultivate other free-living fungi in the environment but others do not. Leaf cutter ants cut portions of leaves and feed them to the fungi after chewing them into pulp, fertilizing it with droppings etc. The cultivated fungi produce structures called gongylidia that the ants feed on. The ants remove the wax from leaves to make it easier for the fungi while the fungi digest secondary chemicals in the plants for the ants. The ants also control bacterial and fungal invaders however they are not always successful. Escovopsis fungus plagues the ant populations and the ants respond by increasing garden weeding and releasing antimicrobial toxins. Crypts on the ant’s exoskeletons houses antimicrobial bacteria, which inhibit the escovopsis, allowing the ants to survive through another mutualism. Positive Interactions: also known as facilitation, those in which one or both species benefit and neither is harmed. In these interactions, the growth, reproduction, and survival of individuals of one or both species is increased (benefits >costs). This can occur when one species provides food, shelter, a substrate to grow on, dispersal of pollen/seeds, reduction of stress or heat, decrease of competitors/predators/parasites etc. There are 2 types: • Mutualism: a mutually beneficial (+/+) interaction between individuals of two species. The costs of one species providing a benefit to the other is highly outweighed by the benefits. This can be species-specific obligate and coevolved or facultative and loosely structured. o Trophic Mutualism: where a mutualist receives energy or nutrients from its partner. In return, the partner may receive limiting nutrients. o Habitat Mutualism: where one partner provides the other with shelter, a place to live, or favourable habitat. They may also change local conditions by improving the ability of the partner survive in a certain environment. Ex. shrimp dig burrows allowing goby fish to live in as well, where the goby acts as eyes for the blind shrimp. Ex. some grasses grow near hot springs but can only survive here if interacting with a certain fungi. o Service Mutualism: interactions in which one partner performs an ecological service for the other such as pollination, dispersal, defense against herbivores/predators/parasites etc. These mutualists are often also trophic mutualists. • Commensalism: an interaction between individuals of 2 species in which individuals of one species benefit while those of the other species do not benefit but are unharmed (+/0). The relationship is always facultative for the non benefitting species, thus no evolution of the non- benefitting species. Ex. skin bacteria, organisms that live in kelp forests, understory plants in the rainforest etc. Symbiosis: a relationship in which individuals of the two species live in close physiological contact with each other. These relationships can range from parasitism (+/-) to commensalism (+/0) to mutualism (+/+). Mycorrhizae: symbiotic associations (usually mutualistic) between plant roots and various types of fungi. The fungi increase the surface area over which the plants can extract water and nutrients from the soil. The fungal extensions from the roots are known as hyphae. The fungi also protect the plants from pathogens and increase the University of Toronto Created By: Lindsay Arathoon 36 plants growth and survival in the process. In return, the fungi is supplied with carbohydrates. There are 2 types: • Ectomycorrhizae: when the fungal partner grows between the root cells and forms a mantle around the exterior of the root, extending into the soil. • Arbuscular Mycorrhizae: when the fungal partner grows further into the soil and grows between and into some root cells. The extensions into the soil are much larger than with ectomycorrhizae. Coral-Algae Mutualism: the coral provides the algae with a home, nutrients, and access to sunlight while the algae provides the coral with carbohydrates from photosynthesis. Lichens: an organism composed of fungi and algae, with 14,000 “species” varying in shape, colour, size etc. Most of these forms can live alone. These are made of 3 layers, the upper and lower cortices and the medulla. These 3 regions are separated by the algal zone. Upon first contact, the fungus recognizes the algae, penetrates it causing death of many algal cells, and the algal cells walls become permeable so they can supply the fungus with sugars. Interaction Evolution: different ecological interactions can evolve into mutualism or commensalism. Ex. if a tree grows with lichen on it, the tree may evolve to have more chlorophyll in its leaves to overcome the lichen covering it. Ex. a strain of amoeba was infected with a bacteria, which initially caused the hosts to be smaller, grow slower, and possibly kill the host, but over 5 years the amoeba host became dependant on this bacteria. The species involved in the interaction may also evolve unique features specifically to benefit the other species. Fig-Fig Wasp Coevolution: fig trees contain figs with flowers that are contained within fleshy tissue known as receptacles. The receptacles contain male and female flowers in different locations and which mature at different times (monoecious plant). The flower style ranges from short to long. The fig wasp places its ovipositor into the styles of these flowers and lays eggs, while depositing pollen on the stigmas of short and long styled flowers. The fig wasp larvae are usually deposited in short-styled flowers because the ovipositor is not long enough, thus they eat the seeds produced there. When mature, male fig wasps collect pollen from male flowers and move to other receptacles to lay eggs. Nurse Plants: in some desert environments, the soil below a plant is cooler and more moist than adjacent, unshaded regions, therefore the seeds from the plant are only able to germinate in shaded regions. The adult plant shades the young plants and protects many different species of seedlings. Change in Interaction: depending on the environmental conditions, an interaction may change. Ex. some plants are able to release oxygen into the soil when under hypoxic (flooded) conditions, thus supplying oxygen to other plants through channels. This may be effective at low temperatures but at high temperatures, this can result in negative outcomes for plants without this oxygen channel. Relative Neighbour Effect (RNE): the target species growth with neighbours present minus its growth when neighbours were removed. Neighbours have a positive effect on the target species at high elevation but not at low elevation. Since the environment at high elevations tend to be more extreme with cold temperatures, this suggests that positive interactions are more common in stressful environments. University of Toronto Created By: Lindsay Arathoon 37 Obligate Mutualism: when the species interactions are species-specific and the species involved in the interaction depend on one another for survival. Ex. leaf cutter ants. This leads to evolution so the individuals of each species can develop features that benefit the other species. Facultative Mutualism: non-obligate mutualism (or commensalism) may result due to changes of conditions causing the costs to outweigh the benefits. This results in little to no coevolution and is likely to undergo interaction changes. The interactions are not altruistic since the one mutualist may withdraw its rewards with environmental changes and the partners use each other for their resources. Ex. if the environment changes such that a plant does not require the help of mycorrhizal fungus, it will obtain nutrients on its own and stop rewarding the fungus since the costs begin to outweigh the benefits. Paramecium Bursaria: form an interaction with a photosynthetic algae so it can receive extra energy in return for protection of the algae. This relationship does not exist in dark conditions and if the P bursaria dies, the algae detaches and finds a new one. Cheaters: individuals that increase their production of offspring by overexploiting their mutualistic partner. If the overexploitation occurs, it is unlikely that the mutualism will last since there is likely cost outweighing benefits for the exploited partner. However, it may persist if the cheating results in penalties, where the advantage gained by cheating is reduced. Ex. a yucca plant will selectively abort flowers if a yucca moth lays too many eggs in it because then too many of its seeds will be eaten. Effects on Population Distribution: affected by mutualism and commensalisms. These affect abundances of organisms Ex. ants on the bullhorn acacia plant maul herbivores or other plant competition that come nearby it, thus increasing the growth and survival of the plant, allowing it to grow nectaries and beltian bodies in return for food and a home with an overall effect of increasing the plant and ant abundance. These interactions also affect distributions, since in obligate interactions, neither can exist in regions where their partner is absent. The dominant species usually determines the distribution Ex. trees determine where fungus grows. Community Diversity: affected by mutualistic interactions. If one mutualist in an interaction is removed, it results in a dramatic decrease in the number of species and abundance in the region they were removed. Ex. cleaner fish clean the mouth of larger fish, but are not eaten because the energy gained by eating the fish is outweighed by the benefit of the mouth cleaning. This contributes to fish diversity and abundance. Ecosystem Properties: in many cases, the mutualism can cause an increase in the net primary productivity and nutrient cycling in an ecosystem. Ex. mycorrhizal associations with plants can increase plant growth and thus NPP. Chapter 15: The Nature of Communities Algae Case Study: a species of algae known as Caulerpa taxifolia found in the Carribbean. This species was found in the Mediterranean sea in high densities, which was unusual because it is normally found in warm waters. They wanted to know how it migrated, how it could survive in such temperatures, where else it existed, and how it interacted with other algal species. It was found to release toxic secondary compounds to keep fish away. It also had been released from a museum unintentionally which explains its colonization. It has been found that the algae controls seagrass levels, University of Toronto Created By: Lindsay Arathoon 38 harbours sediments along its roots to change the seafloor and causing decrease in species composition. Communities: groups of interacting species that occur together at the same place and time. Interactions are vital to community existence and are synergistic, giving the community its character and function and allowing it to exist as something more than the sum of its parts. The interactions can be positive, negative, neutral, direct, indirect etc. These can be defined in 2 ways: • Physically: the community is defined by physical characteristics Ex. all the species in a sand dune, stream, etc. • Biologically: the community is defined by biological characteristics, implying interactions Ex. all the species associated with kelp forests, coral reefs etc. NOTE: it is common for ecologists to define communities based on specific interactions or questions they have, since knowing all species within a community is not practical. Guild: a group of species that use the same resources even though they are taxonomically different. Ex. birds, bees, and bats that feed on flower pollen are a guild of pollen-eating animals. Functional Group: a subset of community that includes species that function in similar ways but may not use the same resources. Ex. mosquitoes and aphids have similar mouthparts but they feed on different organisms. Food Webs: organize species based on their energetic interactions. They describe trophic relationships but not the strength of those relationships. These can be confusing because some species take on different roles in the food web based on their symbioses with other organisms, their life cycle stage, if they are omnivores. Food webs also do not include horizontal interactions such as competition or positive interactions. Trophic Levels: organize food webs, groups of species that have similar ways of obtaining energy. The lowest level contains primary producers (autotrophs), which are fed on by primary consumers (herbivores) at the second level. The primary consumers are fed on by the secondary consumers (carnivores). Tertiary consumers (carnivores) can feed on primary and secondary consumers. Interaction Web: introduced to describe the trophic levels (vertically) and the non- trophic interactions (horizontally) for a better representation. Community Structure: the set of characteristics that shape a community. Species diversity and composition are important to community structure. Community structure also provides a quantitative basis for generating hypotheses and experiments relating to understanding how communities work. Species Diversity: the most commonly used measure of community structure. It is the number of species within a community, but combines species richness and species evenness. Ex. Imagine 2 communities (A & B) with 4 mushroom species each: community A has a species ratio of 85:5:5:5 while community B has a species ratio of 25:25:25:25. These communities have equal species richness, but species evenness is low in community A and high in community B, which makes community B have higher species diversity than community A. Species Richness: the easiest measure to determine, the number of species within a community. University of Toronto Created By: Lindsay Arathoon 39 Species Evenness: a difficult measure to obtain, describes the proportion of different species in a community, or the commonness or rarity, which requires knowledge about their abundances relative to other species. Shannon Index: the most commonly used index to measure species diversity quantitatively, given by H = -Σpiln(pi), where H is the Shannon index value, pi is the proportion/percentage of individuals found in the ith species, ln is the natural log, (s, found above Σ symbol (not shown), is the # of species in the community). When piln(pi) is calculated for each species within a community, they are added up to get a total H value. The higher H is, the greater its species diversity. Biodiversity: a term used to describe the diversity of important ecological entities spanning spatial scales (genes, species, communities etc). This also involves interconnectedness of individuals, populations, species, and community-level components of diversity. Most studies only take into account species richness and abundance. Biodiversity is measured by taking the phenotypes, genetics, and ecosystem function into account. Population Viability: the ability of a population to persist, which affects species persistence and diversity, which affects the species diversity within communities. Rank Abundance Curves: a representation of the commonness or rarity of species in communities. These plot the proportional abundance of each species (pi) relative to others in rank order from the most to least abundant. Ex. considering the mushroom communities, since community A has one dominant and three rare species, this may indicate that the dominant species has a negative effect on the others (which does not occur in community B, but tells us about the importance of some species while their interactions are unknown. McCaig et. al: determined species diversity and rank abundance curves for two soil bacterial communities. The bacteria was first sampled from undisturbed and fertilized pastures then used 16s ribosomal DNA sequence analysis to determine DNA sequences for species identification and phylogenetic grouping. 275 species were identified and grouped into 20 taxonomic groups and found that the community structure of the two soil communities were similar: there were few abundant species and many rare species. Species Accumulation Curve: the point where no more sampling will result in the capture of new species. These curves are calculated by plotting species richness as a function of sampling effort, where each data point represents the total number of individuals and sampling effort up to that point. This idea does not apply to reality because new species are always being found. Hughes et. al: used species accumulation curves to determine how communities differ in the relationship between species richness and sampling effort. Sampling was done for 5 different communities then standardized by calculating the total number of individuals and species that had been sampled up until that point. No leveling off was seen in highly diverse communities and additional sampling would be required to get an idea of species richness. Species Composition: important to community structure not shown in species diversity indices. It is the identity of species present in the community. The species diversity between 2 communities may be the same, but the actual species (species composition) within each community can be different. University of Toronto Created By: Lindsay Arathoon 40 Direct Interactions: trophic and non-trophic interactions that occur between two species. Indirect Interactions: when the relationship between two species is mediated by a third (or more) species. The addition of the third species creates more effects to change the outcome of the original interaction. Ex. social interaction: A is friends with B, who meets another friend C. C takes up all of B’s time from friend A. The friend C then becomes friend A’s enemy because C caused A’s friendship with B to decline even though A did not directly interact with C. These interactions are often discovered by accident when a species is removed for study. There are 3 types: • Trophic Cascade: when the rate of consumption at one trophic level results in a change in species abundance or composition at lower trophic levels. Ex. sea otters eat sea urchins (direct, negative), which feed on kelp (direct, negative). By the otter reducing the sea urchins, they are indirectly and positively affecting the kelp and the kelp indirectly positively affects the otters by providing the urchins with food (increasing urchin abundance). • Trophic Facilitation: when a consumer is indirectly facilitated by a positive interaction between its prey and another species. Ex. Juncus plant facilitates the growth of the Iva plant (but not vice versa), which is fed on by aphids. Without juncus, the soil salinity increased and oxygen level decreased making conditions for Iva unfavourable since juncus normally shades the soil from evaporation and its arrenchyma tissue moves oxygen into the soil. Without juncus, Iva abundance decreases, and thus the aphids are left with little food source. • Competitive Networks: competitive interactions among multiple species in which every species negatively interacts with every other species. This maintains species richness and explains the coexistence of competitors. These networks buffer strong direct competition to make competitive interactions weaker/diffuse. Different species act on each other to prevent each other from outcompeting other species. Interaction Strength: the effect of one species on the abundance of another species, measured experimentally by removing one species (the interactor species) from the community and looking at its effect on the other species (target species). If removal of the interactor species results in a decrease in the target species, the interaction is strong/positive but if it results in an increase in the target species, the interaction is strong/negative. This is not well understood due to the large numbers of species in each community. This can be measured by ln[(C/E)/I] where C is the number of target individuals in the presence of the interactor, E is the number of target individuals in the absence of the interactor, I is the number of interactor individuals, and ln is natural log. Menge et. al: measured the interaction between starfish and its predation on mussels in wave-protected and wave-exposed areas, showing that wave-protected areas had larger interaction strength. This was due to the inability of starfish to feed when subject to waves. Ocean acidification due to increased CO2 from global warming may lead to weakening of the skeletons, which may affect the interaction of starfish with mussels. Dominant Species: also known as foundation species, have large, community-wide effects on other species and diversity by providing food or habitat and/or are good competitors for space, nutrients, or light and contribute large biomass. Ex. trees Ecosystem Engineers: create, modify, and maintain the physical environment for themselves and other species. Ex. trees provide habitat, soil aeration, soil stabilization, University of Toronto Created By: Lindsay Arathoon 41 stabilize temperature/wind/sun exposure/rain, seeds and leaves for food, fallen logs and branches for seedling growth etc. Keystone Species: strong interactors that have large effects in relation to their abundance/biomass (usually indirectly). Ex. otters are a keystone species by indirectly influencing kelp abundance or beavers building dams create wetlands to increase species diversity. Context-Dependent Species Interaction: where interactions change based on the context Ex. changes in environmental conditions, population density etc. A highly-dense community with limited resources would see more competitive interactions than a low- density community. This may cause keystone or dominant species to have role in some contexts but not others. Cladaphora Glomerata Study: in northern California, it was found that when this algal species, which are preyed on by herbivorous insects, are subject to flooding over winter, their predators are wiped out and they produce large blooms the following spring due to increased light and nutrients causes this. By midsummer, they detach from rocks and cover the river. This is also when midge larvae feed on and live within them. These midges are fed on by small fish and larvae, which are eaten by steelhead and roach fish, thus supporting 4 trophic levels. Without the flood, only 2 trophic levels are supported and the herbivorous insects feed on the algae (with no predator to control them). Chapter 16: Change in Communities Volcano Case Study: Mt St. Helens was known to be a snow-covered mountain with rich, diverse ecosystems, alpine meadows, home to many plants and animals, until it suddenly erupted, causing a massive avalanche and wave of debris, burning forests, decreasing the depth of nearby lakes, and covering deserts, forests, grasslands etc with ash, producing new habitats with no life forms. Today, scientists are still examining the recovery of life forms in the regions surrounding the volcano. The disturbances varied depending on the distance from the volcano and ecosystem. Some organisms were able to survive if buried in the snow, burrows, or ice-covered lakes. Gophers burrowing moved soil contents around to improve grasslands and form tunnels for frogs to move between ponds. Despite this, the amphibian species richness has not improved back to normal conditions. Succession: the change in the species composition of communities over time, driven by disturbance and stress. This is a result of abiotic and biotic agents of change, resulting in the colonization and extinction of species. These changes can also be subtle, catastrophic, natural, or human-caused. Ex. unusually high water temperatures causing loss of algae-coral symbioses leading to coral bleaching, rising ocean levels causing less light for algal photosynthesis, and acidification of water dissolving coral skeletons, causing their replacements. If not restored, the corals will die allowing for new species to come in. There are 2 types: • Primary Succession: involves the colonization of habitats that have no inhabitants as a result of a catastrophic disturbance. This is a very slow process because the first arrivals (pioneers or early successional species) tend to face harsh, inhabitable conditions lacking basic resources Ex. water, soil etc. These University of Toronto Created By: Lindsay Arathoon 42 species must be able to tolerate such conditions and transform the habitat into useable space. • Secondary Succession: involves the establishment of a community in which most but not all of the organisms or organic constituents have been destroyed by a disturbance such as fire, wind, logging, herbivory etc. Abiotic Factors: physical factors and features of the environment required for growth, reproduction, and survival that cannot be consumed. Ex. temperature, pH, salinity, waves, water supply, chemical composition, solar radiation, volcanic activity etc which change over days, years, 100k years etc. • Disturbance: drives succession, an abiotic agent of change that physically injures or kills individuals, creating opportunities for other individuals to grow and/or reproduce. These can be abiotic Ex. a tsunami or biotic Ex. competition. The intensity of the disturbance describes how much damage and death is caused while the frequency describes how often the disturbance occurs. • Stress: drives succession, when an abiotic factor reduces the growth and reproduction of individuals and creates opportunities for other individuals. Biotic Factors: referring to the living components of a natural system Ex. competition, negative interactions. These interact with abiotic factors to change communities Ex. ecosystem engineer such as a beaver changing the abiotic environment to cause species replacement. Climax: a stage of succession that is the stable end point experiencing little change until an intense disturbance occurs, bringing it back to its original state. Whether succession will ever lead to a stable endpoint is unknown. Henry Cowles: studied successional sequence of vegetation in sand dunes. The dunes continually grow as new sand is deposited at the shoreline, allowing him to infer that the plants furthest from the lake’s edge were the oldest. Different locations on the dunes showed different successional stages, allowing him to predict changes in community that would occur beyond his lifespan (space for time substitution). Frederick Clements: believed plant communities were like superorganisms, groups of species working together towards a deterministic end, where succession had a beginning (birth), middle (adult life), and end (death). Each community has its own life history that will reach a stable end point if undisturbed known as a climax community. Henry Gleason: thought that communities were the random product of fluctuating environmental conditions acting on individual species and were not the predictable or repeatable result of coordinated interactions among species. Each community is the product of a particular place and time and thus is unique. Charles Elton: influenced to write a book because of Cowles, Clements, and Gleason. He believed organisms and the environment interact to shape the direction of succession while acknowledging the role of animals and not just plants. Facilitation Model: by Connell and Slayter and inspired by Clements, describes situations in which the earliest species modify the environment in ways that benefit later species, but hinder their own continued dominance. These species are stress- tolerant, good at engineering habitat. Over time, this leads to a climax community composed of later species only, that do not facilitate other species and are only displaced by disturbances. University of Toronto Created By: Lindsay Arathoon 43 Tolerance Model: by Connell and Slayter, assumes that the earliest species modified the environment in ways that were neutral, thus not benefitting or inhibiting later species. These species have life histories allowing them to grow and reproduce quickly but disappear over time, while later species have life histories allowing them to be better adapted to environmental stresses. Inhibition Model: by Connell and Slayter, assumes that early species modify conditions in negative ways that hinder successional species. This inhibition is broke when a disturbance or stress decreases the number of inhibitory species. Later species have life histories allowing them to be better adapted to environmental stresses. NOTE: once colonization has been established, further colonization can only occur with more disturbance or death to individuals existing there. Also, no one model fits any one community. Glacial Retreat: in Glacier Bay Alaska, the melting of glaciers led to community change reflecting primary succession over many centuries. As the glaciers retreat, they leave behind rock (glacial till) and forests had grown in regions that were once covered in ice and continued to increase in species richness and composition, and increased soil organic matter and moisture (due to growth of N-fixing bacteria) with time and distance from the melting glaciers. This was observed by William Cooper, a student of Cowles (this was his space for time substitution). He set permanent plots that are still examined today for changes. Pioneer Stage: in the first years after a habitat is exposed Ex. by glacier retreat, there are few species present. From 30, to 50, to 100 years after glacial retreat, larger and larger trees begin to grow and the species richness increases until about 200 years. Salt Marsh: made up of different species compositions and physical conditions at different tidal elevations. Dead plant material, known as wrack, smothers and kills plants on the shoreline/terrestrial border, creating bare patches where secondary succession occurs. Salinity here is high because the lack of shade causes water evaporation. Rock Intertidal Communities: disturbances here are created by waves, which remove organisms from rocks or propel debris onto them. The stresses caused by low tides expose some organisms to high/low air temperatures, which can kill them or prevent them from attaching to the rocks. The resulting bare rocks are regions that are open for succession/colonization. A study by Wayne Sousa found that algae-dominated communities on boulders showed disturbance whenever they were turned over by waves. When patches were cleared on the boulders, succession occurred on these patches over time by Ulva lactuca algae, which would eventually be replaced by the original Gigartina algae. He also found that Ulva inhibits growth of Gigartina, but does not dominate because it is fed on by crabs. When a similar experiment was run with Chthamalus barnacles, it was shown that they were eventually replaced by Balanus barnacles due to the tolerance theory. The Balanus was also shown to facilitate algal growth and protect them from limpet herbivorous snails. Resilience: refers to the length of time for recovery of a community to occur. If this period of time is longer, it is likely the community would change and appear unstable. Resistance: a measure off deviation from the normal range. The ecosystem is stable if it returns to initial conditions. University of Toronto Created By: Lindsay Arathoon 44 Alternative Stable States: when different communities develop in the same area under similar environmental conditions. The larger the area, the more likely is it that similar species will recolonize. John Sutherland: studied alternative states in marine fouling communities including sponges, hydroids, etc. He suspended ceramic tiles from a dock and allowed plankton larvae to colonize them. After 2 years, he found that tunicates were dominating them (but not in winter). Other colonizers were unable to colonize on tiles dominated by the tunicate, making it a stable state. When new tiles were added, schizoporella acted on them, and the tunicate was unable to colonize those. When more tiles were added with cages to protect from fish predators, the tunicates were dominant in protected cages while schizoporella dominated unprotected cages, suggesting the tunicate’s dominance when undisturbed by predators and winter. The original conditions were seen because the tunicates reached a size that excluded predators. This shows multiple stable states. Hysteresis: the inability to shift back to the original community type even when original conditions are restored. The change might occur due to a change in one or more dominant species, and if sufficiently large, the change may lead to hysteresis. Chapter 18: Species Diversity in Communities Biofuels: liquid or gas fuels made from plant material (biomass) Ex. ethanol, biodiesel, etc made from corn/soybeans etc. These can be produced as long as crops are grown. The cons of these fuels is that they require a lot of land that could be used for food production, and fossil fuels are required to make fertilizers used to grow the crops for biofuels and to transport the biofuels. Carbon Neutral: the amount of CO2 produced by burning biofuels matches the amount taken up by the plants from which they are made. Community Membership: controlled by multiple factors such as regional species pools, dispersal ability, abiotic conditions, and species interactions that act as filters to allow certain species in certain communities and keep others out. You may end up with the same or different number and types of species from the species pool after the filters are applied. Regional Species Pool: the pool of species within a region, also called gamma diversity. This provides an upper limit on the number and types of species that can be present in a community. Dispersal is important to the diversity in these pools, which is greatly affected by humans, who cause/prevent dispersal Ex. in the ballast water of cargo ships entering docks on other regions of the world. Abiotic Filter: even though a species can disperse to a new community, it may not be accepted if it cannot put up with the abiotic factors there Ex. marine organisms that can’t live in a fast-flowing water. Competitive Exclusion Principle: two species that use a limiting resource in the same way cannot coexist. No two species will occupy the same niche. Coexistence: species depend on other species for growth, reproduction, and survival. If the species that are depended on are not present in the community, the membership into the community by dependant species is not gained. Otherwise, a species may be excluded from a community by competition, predation, parasitism, or disease. University of Toronto Created By: Lindsay Arathoon 45 Biotic Resistance: the failure of some non-native species to become incorporated into communities is attributed to interactions with native species that exclude the slow population growth of the non-native species. Resource Partitioning: when a resource available in a community is used by different organisms in different ways to overcome competition and allow coexistence and species richness. The resource lies on a spectrum depending on prey size, nutrient types, and habitat types, where each species and their needs falls along this spectrum somewhere. Less overlap, broad resource spectrum allowing for use by more species, or evolution of character displacement (change in form of competition) can lead to increased species richness and decreased competition. Community Diversity: there are 3 different theories controlling community diversity: • Equilibrium Theory: ecological and evolutionary compromises leading to resource partitioning. This assumes that species have reached a stable carrying capacity and that resources are limiting. Some believe this is unrealistic since populations are always fluctuating in space and time. • Nonequilibrium Theory: fluctuating non-equilibrium conditions such as stress, disturbance, and predation can mediate resource availability and thus affect species interactions and coexistence by keeping dominant species from monopolizing resources. Therefore, competitive exclusion cannot occur by the dominant species and coexistence will be maintained. • Neutral Theory: species do not differ and diversity patterns are a product of dispersal, speciation, and demographic stochasticity. This can predict diversity patterns in diverse systems, even when all species are competitively equivalent and use the same resources. The problem is that no species are equivalent. Stephen Hubbel: wrote a book in 2001 on neutral theory. In this case, individuals die at random, the spot they were taking up is colonized at random by any other species in the community. Eventually, all species go extinct locally except one if no new species are introduced. New species are brought in by immigration and speciation. Scheffer and Van Nes: in 2006 showed with computer simulations that evolution would produce groups of similar species. MacArthur: studied warblers in North America, by recording their feeding habits, nesting locations, and breeding territories to determine how they coexist. He found that the birds were using different parts of the tree canopy in different ways. There was also a positive relationship between bird species diversity and foliage height diversity (number of vegetation layers, indicating habitat complexity). Resource Ratio Hypothesis: proposed by Tilman, where species coexist by using resources in different ratios or proportions. He studied 2 forms of diatom freshwater algae and their consumption of silica. Growing them together they differed in their ratio of silica and phosphorus use, where one species dominated when silica:phosphorus ratio was low and the other dominated when the ratio was high. Coexistence occurred when both molecules were limited to both species. Hutchinson: came up with the “paradox of the plankton”, which described that all phytoplankton species compete for the same resources Ex. P, N, etc. that are likely to be evenly distributed in lake water, however the conditions in the lake change seasonally, preventing any of the species from out competing each other, allowing for coexistence and increased diversity. The time required to competitively exclude another University of Toronto Created By: Lindsay Arathoon 46 species (tc) and the time it takes for environmental variation to act on population growth of the species (te) are part of this theory. Coexistence cannot occur when competitive exclusion occurs more rapidly than the environment is changing (tc>>te), and when competitors are adapted to a rapidly changing environment, tc<
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