Community Ecology APES Chapter 8

8-1 Community Structure and Species Diversity Ecologist use 3 characteristics to describe a biological community. Physical appearance- sizes, stratification, and distribution of its population and species Edge Effect Species diversity- a combination of numbers of different species (richness) and abundance of individuals with each species (species evenness) High richness usually means low evenness (few #’s per species) Factors affecting diversity are latitude in terrestrial communities and pollution in aquatic communities.   Niche structure- the number of ecological niches, similarities/differences, and interaction of species with each other.

Species Equilibrium model (Theory of island biogeography) The number of different species on an island (species richness) is determined by how fast a species arrives, how fast old species become extinct, island size and distance from mainland. Important: Balance between rate of immigration of species and rate of extinction of existing species. Size of island (smaller has less diversity) and distance from mainland (closer to mainland, increases species richness)

General Types of species Native: species that normally live and thrive in a particular ecosystem Non-native species: species that migrate into an ecosystem or are deliberately or accidentally introduced into an ecosystem by humans. Also known as: Exotic/ Alien Problems caused by Non-native species: the non-natives have no natural enemies so they can thrive in the new ecosystem and crowd out the native species: Examples: Melaleuca plants, Burmese pythons, iguanas

Indicator Species: species that serve as early warnings that a community or ecosystem is being damaged or changed: Birds are good indicators because: Trout and macro-invertebrates are good indicators of: Amphibians indicate:

Keystone species: species that play a pivotal role in the structure, function, and integrity of an ecosystem because Their strong interactions with other species affect the health and survival of these species They process material out of proportion to their numbers and biomass Keystone species: Pollinate Scatter seeds Modify habitats Predation to control prey populations Help plants get nutrients Recycle animal waste Examples:

Foundation Species- shape communities by creating and enhancing habitat for other species Elephant tearing down tree

5 Types of Species Interactions

Competition: Two or more animals competing for the same resources. Two Types: Intraspecific: competition between members of the same species (mates) Interspecific: competition between members of two different species (food, space, sunlight)   The more a species niche overlaps, then the more competition. This can lead to one species migrating, adapting new behaviors or dying out. Over a long time scale, adaptations lead to RESOURCE PARTITIONING (warblers) or NICHE SPECIALIZATION (owls/hawks)

Warblers and resource partitioning

Species Interactions (continued) Predation: members of one species feed directly on all or part of a living organism or other species. They do not live on or in the other species. One species is clearly harmed and the other clearly benefits. Benefits: Predation can be a good thing for the population of prey species as predators often weed out the sick and dying animals, thereby reducing competition amongst the prey species and controlling population growth. Also, enhances the passing of successful genetic traits to the next generations. (Sharks)

Predators have characteristics that help them catch prey, such as: Running fast, ex. Good eyesight, Ex. Hunting in packs, ex. Camouflage for ambush, ex.

Prey have characteristics that help them escape predators, such as: Run fast Good sense of smell and eyesight to alert them to the presence of predators Protective shell Spines Camouflage Chemical warfare like poisonous skin Foul smells Bad tasting Warning coloration Mimicking a predator Examples:

Symbiosis: a long lasting relationship in which species live together in an intimate association.

Parasitism: when one species feeds on part of another organism (host) by living on or in the host. In this relationship the host is harmed and the parasite benefits. Examples:

4) Mutualism: symbiotic relationship in which both species involved benefit from the relationship. Ways in which this happens are pollination, providing food, and providing shelter. Examples:

Commensalism: a symbiotic relationship in which one species benefits and the other species is neither helped nor harmed. For example:

Review Species Interactions Quiz!

Ecological Succession: Communities in Transition Ecological Succession: One characteristic of all ecosystems is that they change over time due to changes in environmental conditions. There are 2 types of succession: Primary and secondary

Primary Succession: Succession that starts with an essentially lifeless area where there is no soil or bottom sediment in an area. Examples include new lava, an abandoned parking lot, land exposed from retreating glaciers, etc. Succession happens in stages: 1) Pioneer species move in and make soil: Ex. Lichens and mosses 2) When enough soil is made and spread out, then plants that are small and close to the ground move in. These plants can live under harsh conditions and usually have short lives. They are called early successional species. Examples: small annuals 3) After hundreds of years ,there is enough soil for Mid-successional species. Examples: small herbs/shrubs 4) As the Mid-successional plants grow they create enough shelter for Late successional species such as: trees.

Secondary Succession: Begins in an area where the natural community of organisms has been disturbed or destroyed, but the soil remains. For example: abandoned farms, burned or cut forests, and heavily polluted streams. Secondary succession occurs in the same way as primary starting with pioneer species and ending with late successional species. Climax community- stable, self-sustaining community at the ending stages of ecological succession.

Disturbances can Affect Succession Some disturbances can be beneficial in the long run like fire, because they increase biodiversity, clear out excess brush, renew nutrients and encourage other species to grow. Some catastrophic disturbances can convert the ecosystem back to a lower level of succession. It’s an ongoing struggle to always progress towards a climax community.

Ecological Stability and Sustainability 3 aspects that lead to stability of a living system Inertia/persistence – ability of a living system to resist being disturbed or altered Constancy- ability of a living system to keep its numbers within limits of available resources. Resilience- ability of a living system to repair damage after an external disturbance that is not too drastic. Complexity- Populations with more biodiversity are more stable. More biodiversity means greater primary productivity and more resilience.

Everything is Connected! There is overwhelming evidence that human disturbances are disrupting important ecosystem services that support and sustain all life and economies. Taking action to prevent these disruptions even if they haven’t happened yet is the precautionary principle. (“Better safe then sorry” approach)