Community Structure and Biodiversity Chapter 46

Ecosystem—all the organisms that live in a place, together with their physical environment Biome—a group of ecosystems that share similar climates and typical organisms

Food Web

Ecological Pyramids

Ecological Pyramids

Trophic Level Review List a food chain with at least 4 organisms Place them in an energy pyramid Label Autotroph Heterotroph Producer Consumer Primary Secondary Tertiary

The Habitat vs. Niche Habitat Niche The type of place where a species normally lives Niche The unique ecological role of each species in a community Described in terms of conditions, resources, and interactions necessary for survival and reproduction (soil, light, pollinator requirements, )

Effects of Competition in Salamanders Where two species coexist, competitive interactions suppress the populations of both

46.4 Predator–Prey Interactions Predators are consumers that get energy and nutrients by capturing, killing, and eating prey Relative abundances of predators and prey shift over time in response to species interactions and changing environmental conditions

The Canadian Lynx and Snowshoe Hare

Coevolution of Predators and Prey Predator and prey populations exert selective pressures on one another Genetic traits that help prey escape will increase in frequency Defensive improvements select for a countering improvement in predators

Some Physical Adaptations of Prey Camouflage Body shape, color pattern and behavior that make an individual blend in with its surroundings Warning coloration Many toxic or unpalatable species have bright colors and patterns that predators learn to avoid Mimicry A harmless animal looks like a dangerous one (yellow jacket and mimic

Adaptive Responses of Predators Predators find ways of avoiding prey defenses Grasshopper mice and spraying beetles Koalas and noxious eucalyptus leaves Predator speed Predator camouflage

Nitrogen Cycle

Photosynthesis

Respiration (not just for animals!!!!)

Symbiosis - “life together” Parasitism – one species benefits the other is harmed Mutualism – both species benefit Commensalism - one species benefits, the other is neither helped or harmed

46.8 Ecological Succession Ecological succession is a process in which one array of species replaces another over time It can occur in a 1) Barren habitat such as new volcanic land (primary succession) 2) Disturbed region in which a community previously existed (secondary succession)

Primary Succession

Secondary Succession

Pioneer Species Pioneer species are opportunistic colonizers of new or newly vacated habitats Primary succession begins when pioneer species such as lichens and mosses colonize a barren habitat with no soil Pioneers help build and improve soil for later successional species

Observed Primary Succession: Alaska’s Glacier Bay

Experiments in Primary Succession: Mount Saint Helens (Crash course) Mt. St. Helens – 1980 10 years later = pioneer species 12 years later = Doug Fir

Factors Affecting Succession Which species are present in a community depends on (1) physical factors such as climate (2) biotic factors such as which species arrived earlier (3) the extent of disturbances

Experiment: Loss of a Keystone Species In a rocky California intertidal zone, predation by sea stars (Piaster ochracenus) normally controls mussel populations When sea stars were removed, mussels crowded other invertebrates out (competitive exclusion) – species diversity fell from 15 species to 8

Species Introductions Tip the Balance Geographic dispersal happens in three ways: A population may expand its home range by slowly moving into outlying regions A population might be slowly moved from its home range by continental drift Individuals might be rapidly transported over great distances by other agents (jump dispersal)

Species Introductions Humans are a major cause of jump dispersal Intentional or accidental introduction of exotics Exotic species A species that is dispersed from its home range and permanently established in a new community Often outcompetes native species, untroubled by competitors, predators, parasites and diseases that kept it in check in its own habitat

46.10 Exotic Invaders Nonnative species introduced by human activities are affecting native communities on every continent Knapweed Zebra Mussels Have been found at checkpoints in MT Need a high amount of Ca (limited water)

The Rabbits That Ate Australia Two dozen European rabbits released in 1859 became 200 to 300 million, turning shrublands and grasslands into eroded deserts Cane Toads....are you ready for this???

Gray Squirrels Versus Red Squirrels The gray squirrel, native to North America, has become a pest in Britain, where it outcompetes native European red squirrels Gray squirrels also carry a virus that kills red squirrels – but not grays; imported grays now outnumber reds 66 to 1

Biogeographic Patterns Generally, species richness is highest in the tropics and lowest at the poles Tropical habitats have conditions that more species can tolerate (sun, rain, growing season) Tropical communities have often been evolving longer than temperate ones Species richness may be self-reinforcing

Island Formation When a new island forms, species richness rises over time, and then levels off Island of Surtsey formed in the 1960s Vascular plants became established in 1965 Establishment of nesting seagulls in 1986 increased rate of introduction of new species Equilibrium has not yet been reached