Community Ecology: Structure, Species Interactions, Succession, and Sustainability Miller Chapter 8

Community Structure The structure of an ecosystem described in terms of: Physical appearance – Things like size, stratifications, & distribution of its population & species Lots of differences in aquatic life zones Size differences of vegetation patches Differences in abiotic factors at edges of boundaries & ecotones  edge effects Species diversity - # of different species Species abundance - # of individuals of each species Niche structure - # of ecological niches, how they compare to each other, & species interactions Section 8-1

Biodiversity The World’s Places with the Most Biodiversity places are: Rain forests Coral Reefs Deep Sea Large tropical lakes In general, high biodiversity = low species abundance

Species Diversity Species Diversity is affected by: Latitude – species diversity decrease as you move away from the equator Latitudinal species diversity gradient leads to the highest species diversity in tropical areas and lowest in the polar areas Depth in aquatic systems – diversity increases from the surface to 2,000 meters then begins to decline until sea bottom is reached, where species diversity is high. Pollution in aquatic systems – the more pollution, the less species diversity & abundance

Species Diversity con’t In terrestrial communities, species diversity increases with increasing solar radiation, increased precipitation, decreasing elevation, & seasonal variations.

Species Equilibrium Model (Theory of Island Biogeography) States that the # of species on an island depends on the rate at which new species immigrate to the island & the rate at which species become extinct on the island. Size & degree of isolation determine the number of species found on an island. This suggests that a small island will have a lower species diversity because there is generally lower immigration because it is a smaller target & a higher extinction rate because of resource limitation. Colonization Extinction

Gaia Hypothesis Hypothesis that earth is alive and can be considered a system that operates and changes by feedback of information between its living and nonliving components.

Types Of Species Native Non-native Indicator Keystone Section 8-2

Native Species Species that normally live in a particular ecosystem

Non-native Species Species that migrate or are deliberately or accidentally introduced into an ecosystem AKA: exotic species, alien species Ex. African Bees

Indicator Species Species that are indicators of problems within an ecosystem or community Ex. birds, fish, snails

Keystone Species Species whose interactions with other species affect the health & survival of these species. In short, these are organisms that without which the ecosystem could collapse. Ex. dung beetles

Keystone Species con’t Roles: Pollination of flowers by bees, hummingbirds, etc. Seed dispersal by bat feces Habitat modification (elephants, bats, beavers) Predation of species by top carnivores Top predator species – help regulate populations by feeding on certain species, creating a stabilization effect. Loss of a keystone species can cause population crashes & extinctions of species that depend on the keystone species.

Community Interactions Intraspecific competition Competition between members of the same species for the same resource Ex. dandelions competing for space & nutrients Section 8-3

Territoriality Organisms of the same species patrol or mark the area around their home, nest, or feeding ground and defend it Ex. robins, hummingbirds Good territory = abundant food supply, good nesting site, few predators, etc. Disadvantages: exclusion of male members from breeding & large energy expenditure during defending the territory Community Interactions

Community Interactions con’t Interspecific competition Competition between members of different species for food, space, & other limited resources Interference competition – limiting access to a resource Exploitation competition – one species can exploit/obtain the common resource faster than another

Competitive Exclusion Principle No 2 species can occupy the same niche at the same time

Avoiding Competition Resource partitioning Dividing scarce resources so that competing species use them at different times, in different ways, or in different places Figure 8-9 Miller p. 175

Predator-Prey Relationships Predation – member of one species feeding directly on all or part of a living organism of another species Predator – the killer/eater  benefits Pursuit & ambush (carnivores) Prey – the killed/eaten  harmed (usually) Prey can also benefit because weak members of a species will be killed off thereby freeing up resources for the more fit members Defense mechanisms: mobility, keen sight & smell, protective armor, bark or spines, camouflage, chemical warfare.

Symbiosis species living together in close association Types: Parasitism Mutualism Commensalism

Parasitism One species lives in or on another species & harms it (+,-) Host – lived on/in  harmed Parasite – lives within the host  benefits Smaller than the host Weakens host over time, but rarely kills it Ex. heartworms, ticks, tapeworms, mosquitoes Ascaris Guinea Worm (Dracunculus medinensis)

Mutualism Both species benefit from the interaction (+,+) Protection Reproductive assistance Being supplied with food 3-way mutualism Ants eat from nectar ducts on the caterpillar & the caterpillar eats from the flower. The ants provide protection for both the flower & the caterpillar.

Commensalism One species benefits & the other is neither helped nor harmed (+,ø) Ex. whales & barnacles

Ecological Succession The gradual change in species composition of a given area; some populations grow & some decline 2 Types: Primary Secondary

Primary Succession Occurs in an area where no life has ever been; occurs gradually EX. Island formation as a result of volcanic eruption, rock exposed from melting glaciers Characteristics:

Begins in an area with no soil (terrestrial) or no bottom sediment (aquatic); producers, consumers & decomposers need soil Soil formation begins when pioneer species attach themselves to bare rock. Ex. Lichens, moss They trap wind-blown soil & detritus, produce small amounts of organic matter, and secrete acids that break down rock (weathering). Characteristics con’t

Pioneer species are eventually replaced by small grasses or herbs which grow close to the ground & can flourish in harsh conditions. Midsuccessional plant species  take over following hundreds of yrs of soil formation. These are herbs, grasses, & small shrubs Late successional plant species  occur following the growth of trees that provide the necessary shade. Characteristics con’t

Primary Succession cont’d Figure 8-14 Miller p. 180

Secondary Succession Reestablishment occurring in an area where life once had been; more common EX. Land destroyed by wildfires New plants usually begin to grow in a few weeks

Secondary Succession con’t Figure 8-15 Miller p. 181

Succession and Wildlife Figure 8-16 Miller 182 Succession involves lots of changes in the community structure, so different species are present at various stages of succession.

Succession 3 Factors affect how and how quickly succession occurs: 1. Facilitation – one species makes an area suitable for another species; EX. lichens & mosses role in soil formation 2. Inhibition – early species hindering the growth/establishment of other species; EX. interference competition (chem. warfare) 3. Tolerance – late successional plant species are unaffected by earlier plant species

Succession Disturbances Changes in the environmental conditions that disrupt an ecosystem Can be gradual or catastrophic Not all are harmful Ex. wildfires renew resources in soil, can also discourage or eliminate species thereby freeing up niches

Stability Balance in an ecosystem maintained by constant dynamic changes in response to the changing environment. 3 Aspects of Stability Inertia, or persistence is the ability of a living system to resist being disturbed or altered Constancy is the ability of a living system to keep its numbers and live within its resources. Resilience is the ability of a living system to rebound after a mild external disturbance. Section 8-6

Stability con’t Recent research indicates that ecosystems with higher species diversity have higher net productivities and are more resilient. In these same ecosystems, however, species populations fluctuate more widely. Populations, communities and ecosystems are rarely balanced. Disturbance, fluctuation & change is more the norm.

Precautionary Principle When evidence indicates that an activity can harm human health or the environment, we should take precautionary measures to prevent harm even if some of the cause & effect relationships have not been scientifically established.