Community Ecology, Biodiversity, and Disruptions

  • Community: a group of populations of different species living closely and capable of interacting

  • Habitat: a place or part of an ecosystem occupied by an organism

  • Ecological niche: the role and position a species has in its environment

    • Fundamental niche: the niche potentially occupied by the species if there were no limiting factors (predators, competitors, etc)

    • Realized niche: the portion of the fundamental niche the species actually occupies

  • Interspecific interactions: interactions of individuals from one species with individuals of another species

    • Competition

    • Predation

    • Herbivory

    • Symbiosis (parasitism, mutualism, commensalism)

    • Facilitation

  • Competition: -/- relationship where individuals of different species compete for limited resources

    • Competitive exclusion principle: two species competing for the same resource cannot coexist permanently

      • occurs when two organisms attempt to occupy the same niche (role) in the same habitat

  • One species will outcompete the other or they will divide the habitat (niche partitioning)

  • Predation: +/- relationship where one species (predator) kills and eats the other species (prey) 

    • Predator’s adaptations helps them locate and subdue prey

    • Prey adaptations help the elude predators and defend themselves

      • Cryptic coloration: camouflage

      • Batesian mimicry: harmless species mimics a harmful one

      • Mullerian mimicry: two or more bad-tasting species resemble each other

  • Herbivory: +/- relationship where one organism eats part of a plant or alga

  • Symbiosis: when 2 or more species live in direct contact with one another

    • Parasitism: (+/-) one organism benefits while the other is harmed

    • Mutualism: (+/+) both organisms benefit from the relationship

    • Commensalism: (+/0) one organism benefits and the other is not affected

  • Facilitation: (+/+ or 0/+) when one species has a positive effect on the survival and reproduction of another without intimate association of symbiosis

    • Common in plant species

      • Some plants make the soil more hospitable for other plant species

  • Species diversity (biodiversity): the variety of different organisms within a community

    • Species richness: the number of different species

    • Relative abundance: the proportion each species represents of all the individuals in the community

  • Simpson’s diversity index: calculate diversity based on species richness and relative abundance

  • High-diversity communities are more resistant to invasive species

    • Organisms that become established outside of their native range/ecosystem, usually by human activity

  • Some species play a more pivotal role than others in a community

  • Keystone species: not usually abundant, but other species in an ecosystem rely on them because of their important ecological niches

    • Example: coral

      • Coral reefs serve as a keystone species because many other organisms rely upon it as a source of food and shelter

    • Example: honey bees

      • Bees are a keystone species because they serve as pollinators

  • Keystone species, producers, and essential abiotic and biotic factors contribute to maintaining the diversity of the ecosystem

    • If keystone species were to be removed from an ecosystem it would have a rippling effect 

      • Often ecosystems collapse → trophic cascade

  • Disturbances can also influence species diversity and composition

  • Disturbance: an event that changes a community by removing organisms from it or altering resource availability

    • Fires, droughts, human activities, etc

  • Ecological succession: the gradual process by which the species composition of a community changes and develops over time after a disturbance

    • Sequence of community changes, usually after a disturbance

    • Pioneer species: the first to grow after the disturbance

    • Climax community: stable plant community representing the final stage of succession

  • Primary Succession

    • Begins without soil

    • Pioneer species of bacteria, lichens, and moss break down rock to form soil over many years

    • After a volcanic eruption, glacier retreat, etc.

  • Secondary Succession

    • Existing community is cleared but base soil is still intact

    • Soil contains seeds and spores

    • Pioneer species of grasses and flowers

    • After a fire, flood, etc.

  • Human activity is the strongest disturbance to an ecosystem

    • The main threats to biodiversity are:

      • Habitat loss

      • Endangered species

      • Overharvesting

      • Global change

  • Habitat loss: single greatest threat to biodiversity

    • Agricultural development and urbanization

      • Clear cutting, cattle grazing, farmland

  • Overharvesting: organisms are harvested faster than their population can rebound

    • Harvesting of ivory in elephants (now banned)

    • Overfishing

  • Global change: alterations to climate, atmospheric chemistry, and ecological systems that reduce the capacity of Earth to sustain life

    • Air/water pollution

      • Acid rain

    • CO2 emissions

    • Ocean acidification

  • Human disturbance have lead to a significant increase in the number of endangered species

    • Many species that are now threatened could potentially provide food, medicine, and fibers

    • Scientists believe we are currently in a mass extinction

  • Biogeographical factors: large scale factors that contribute to a range of diversity observed

    • Latitude: species are more diverse in tropics than at the poles due to climate

    • Area: larger areas are more diverse because they offer greater diversity of habitats