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COMMUNITY ECOLOGY Community Structure • Depends on 4 factors: –Physical appearance –Species diversity –Species abundance –Niche structure Factor 1: Physical Appearance • A) biomes –Aquatic ecosystems B) Differences within communities ex. (edge effect) Edge Effects • Transitions between ecosystems (ecotones) such as forest and field: differences in sunlight, temp., wind, etc. • Some animals like “edges” (deer, quail) Edge Effects • Due to habitat fragmentation, “edges” are on the rise • Negative impacts: –Increasing predation, fires, disease, parasitism, road mortality –Creates barriers preventing species from finding food, mates Edge Effects – Habitat Fragmentation Edge Effects • Nest parasitism Edge Effects • Road Mortality Edge Effects • Preventing mortality by creating “habitat corridors” Factor 2: Species Diversity • Number of different species • 3 factors determine diversity: –Latitude: diversity decreases as you increase latitude (move away from the equator) –Depth: increasing diversity as increasing depth to approx. 2,000 meters, then decreases with depth, until you get to the bottom Factor 2: Species Diversity (con.) 3 factors affecting diversity (con.): pollution: increasing pollution causes a decrease in diversity Factor 2: Species Diversity • Other factors: (in general these cause an increase in species diversity) –Increased sunlight –Increased precipitation –Pronounced seasons Factor 2: Species Diversity • Theory of Island Biogeography (MacArthur & Wilson) • Species number on an island is determined by a balance between 2 factors: –Rate of immigration (new species arriving) –Rate of extinction • Island Biogeography Factor 2: Species Diversity (island) • Rate of immigration and extinction depends on 2 factors: –Size of the island –Proximity to the mainland Factor 2: Species Diversity (island) • The bigger the island, the more diversity –Small islands are a smaller target for immigrators & fewer resources • The closer it is to the mainland, the more diversity –Close island has a higher immigration rate Factor 3: Species Abundance The number of individuals in each species: although tropical rainforests and coral reefs have high diversity, these areas tend to have low species abundance Factor 4: Niche Structure • Number of niches (roles) in ecosystem, similarities and differences between these niches, and species interaction determines niche structure Factor 4: Niche Structure • Different niches in an ecosystem (a niche is defined as the role and organism plays in the ecosystem): –Native –Nonnative (exotic, alien, invasive) –Indicator –keystone Niches • Native: species that normally live and thrive in a particular ecosystem Niches • Nonnative: species that migrate or are accidentally or deliberately introduced into an ecosystem by humans • Can out-compete native species and crowd them out (invasive species) –Exs.: zebra mussels, kudzu Niches -- Invasives • Zebra mussel Niches -- Invasives • kudzu Niches – Indicator Species • Indicators: species that serve as early warnings to damage to an ecosystem • Exs. Migratory • songbirds, frogs Niches – Indicator Species • Migratory songbirds respond quickly to environmental change –Habitat fragmentation in both winter and summer habitat (can’t find suitable nesting sites, increased predation) –Forest interior loving species Niches – Indicator Species • Frogs (25% of all known amphibian sp. are extinct, endangered, or vulnerable) • Eggs have no protective shells to block out UV rays • Adults take in water and air through skin, also absorbing pollutants Niches – Indicator Species • frogs Niches: Keystone Species • Role in ecosystem is more important than abundance or biomass would suggest • Strong interactions with other species • Loss could lead to population crashes or extinctions of other sp. Niches: Keystone Species • Critical Roles: – Pollination – Seed dispersal – Habitat modification – Predation by top predators – Improve ability for nutrient uptake by plants – Efficiently recycle animal wastes Niches: Keystone Species • Pollination and seed dispersal Niches: Keystone Species • Habitat modification Niches: Keystone Species • Predation by top predators Niches: Keystone Species • Recycling of animal wastes Niche Structure: Species Interactions • Species Interactions: – Intraspecific competition – Interspecific competition – Predation – Symbiotic relationships • Parasitism • Mutualism • commensalism Niche Structure: Species Interactions • INTRAspecific competition: competition for resources between members of the same species Niche Structure: Species Interactions (intraspecific) • Allelopathy: one species releases a chemical substance to inhibit growth near it. Ex. Black walnut Niche Structure: Species Interactions (intraspecific) • Black walnut Niche Structure: Species Interactions (intraspecific) • Territoriality:organisms mark and defend an area around home, nest site Niche Structure: Species Interactions (intraspecific) • territoriality Niche Structure: Interspecific • INTERspecific competition: competition between two or more different species for food, space, or any other limited resource –Fundamental niche: the niche a species would occupy if there was no competition Niche Structure: Species Interactions (interspecific) • The more two species’ niches overlap, the more competition –Competitive exclusion principle: one species eliminates another in a particular area because they outcompete for limited resources Niche Structure: Species Interactions (interspecific) • Competitive exclusion principle: Niche Structure: Species Interactions (interspecific) • How do species reduce competition? – Over time, species that compete for the same resources evolve adaptations that reduce competition or overlaps of their fundamental niches – Resource partitioning Niche Structure: Species Interactions (interspecific) • Resource partitioning: dividing up of scarce resources so that species can use them at different times, different ways, or different places –Exs. Hawks hunt by day, owls by night lions take larger prey, while cheetah take smaller Niche Structure: Species Interactions (interspecific) • Resource partitioning and niche specialization Interference Competition • A species may limit another’s access to some resource • Ex. Hummingbird’s defending patches of wildflowers by chasing away other humming bird species Exploitation Competition • Competing species have equal access to a specific resource, but differ in how fast or efficiently they exploit it • Ex. humans Niche Structure: Species Interactions (Predator-Prey) • Predator-Prey Relationship: as prey pops. Increase, after an initial delay, the predator pops. Increase, eventually causing a decrease in prey, thereby after an initial delay, causing a decrease in predator pops… and so on (cycle) Niche Structure: Species Interactions (Predator-Prey) • Predator-prey relationship Niche Structure: Species Interactions (Predator-Prey) Predator-prey – didinium & paramecia Niche Structure: Species Interactions (Predator-Prey) • Seems to harm prey population, but in reality it often reduce sick, aged, weak members • Increase food supply for prey and genetic stock (increasing reproductive success and longterm survival Niche Structure: Species Interactions (Predator-Prey) • How do predators increase their chance for success of prey acquisition? –Speed, stealth, keen senses, cooperation, camouflage Niche Structure: Species Interactions (Predator-Prey) • Camouflage – preying mantis (in memory of Darwin) Niche Structure: Species Interactions (Predator-Prey) • How do prey protect themselves? Prey Avoidance • Protective shell Niche Structure: Species Interactions (Prey Adaptations) • Spines or thorns Niche Structure: Species Interactions (Prey Adaptations) • mimicry Niche Structure: Species Interactions (Prey Adaptations) mimicry • mimicry Niche Structure: Species Interactions (Prey Adaptations) • Poison and warning colors Niche Structure: Species Interactions (Prey Adaptations) • camouflage Niche Structure: Species Interactions (Prey Adaptations) • Changing color camouflage Niche Structure: Species Interactions (Prey Adaptations) • Behavioral strategies Niche Structure: Species Interactions (Prey Adaptations) • Schooling, flocking (safety in numbers) Niche Structure: Species Interactions (parasitism) • Parasitism: one species feeds on part of another; parasite benefits, host is harmed (rarely killed) Niche Structure: Species Interactions (ectoparasite) Niche Structure: Species Interactions (endoparasite) Niche Structure: Species Interactions (mutualism) • Mutualism: the two species involved benefit from the relationship (nutritional, protection, reproductive) –Ex. Lichen:fungi collect and hold moisture, photosynthetic algae provide food –Birds remove parasites from rhinos –Clownfish gain protection from Niche Structure: Species Interactions (mutualism) Niche Structure: Species Interactions (mutualism) Niche Structure: Species Interactions (commensalism) • Commensalism: one species benefits and the other one is neither harmed nor benefited Niche Structure: Species Interactions (commensalism) Epiphytes: use other plants for support, to reach elevations for increased sunlight Ecosystems Respond to Change • Ecological succession: gradual change in species composition of a given area –Primary succession –Secondary succession Primary Succession Ecological succession • Primary succession –Soil formation begins when pioneer species attach themselves to bare rock, over time adding organic material and breaking the rock down further Ecological succession • Pioneer species example: Ecological succession • After patches of soil are built up, small grasses and herbs can grow • Characteristics: – Large pops. Under harsh conditions – Short lives Ecological succession • Next, more grasses, herbs and shrubs, and small trees begin to grow • Characteristics –Need lots of sunlight (shade intolerant) Ecological succession • Finally a mature forest is in place (oak, hickory) – climax community • Characteristics –Shade tolerant Ecological succession Early Successional Species Midsuccessional Species Late Successional Species Wilderness Species Rabbit Quail Ringneck pheasant Dove Bobolink Pocket gopher Elk Moose Deer Ruffled grouse Snowshoe hare Bluebird Turkey Martin Hammond’s Flycatcher Gray squirrel Grizzly bear Wolf Caribou Bighorn sheep California condor Great horned owl Ecological succession Fig. 8.17, p. 190 Ecological succession • Secondary succession: begins when a natural area has been disturbed or removed • Examples: abandoned farmland, burned or cut forests, land that has been dammed or flooded, heavily polluted streams Ecological succession • 3 factors that affect rate of succession –Facilitation –Inhibition –tolerance Ecological succession • Facilitation: one set of species makes an area suitable for species with different niche requirements • Ex. Legumes add nitrogen to soil Ecological succession • Inhibition: early species prevent the growth of other species (allelopathy) Ecological succession • Tolerance: late successional species are unaffected by earlier species Ecological Stability • Stability is maintained only by constant dynamic change in response to changing environmental conditions • 3 factors affect stability: inertia, constancy, resilience Ecological Stability • Inertia or persistence: the ability of a living system to resist disturbance Ecological Stability • Constancy: ability of a living system to keep its numbers within limits imposed by available resources Ecological Stability • Resilience: ability of a living system to bounce back after an external disturbance Ecological Stability • Intermediate Disturbance Hypothesis: moderate disturbance in communities promote greatest species diversity Ecological Stability • Intermediate Disturbance Hypothesis Precautionary Principle • When evidence indicates that an activity can harm human health, we should take measures to prevent harm even if causeand-effect relationships have not been fully established scientifically