Communities

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

Niche

• 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

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

  • Competition

  • Predation

  • Herbivory

  • Symbiosis (parasitism, mutualism, commensalism)

  • Facilitation

Competition

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

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

    • The competitor with even a slightly better advantage will eliminate the inferior competitor

• Niche partitioning: natural selection drives competing species into different patterns of resource use, or different niches

Predation

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

  • Adaptations of both predators and prey have been refined by natural selection

    • Cryptic coloration: camouflage

    • Batesian mimicry: harmless species mimics a harmful one

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

Herbivory

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

Symbiosis

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

  • Parasitism: (+/-) when one organism (parasite) derives nourishment from another (host)

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

  • Commensalism: (+/0) when one organism benefits and the other is neither harmed nor benefited

Facilitation

• 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

Species Diversity

• 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

• High-diversity communities are more resistant to invasive species

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

    • Example: a ship bringing produce from another country may have insects in the crates holding the produce

    • Cause harm to the environment

    • Grow and reproduce quickly

• The intentional or unintentional introduction of an invasive species can allow the species to exploit a new niche that is free of predators or competitors

Keystone Species

• 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 protection

    • 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

Disturbances

• 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

  • Primary succession: a series of changes on an entirely new (previously lifeless) habitat that has not been colonized

• Secondary succession: a series of changes that clears an existing community, but leaves the soil intact

Human Disturbances

• Human activity is the strongest disturbance to an ecosystem

  • The main threats to biodiversity are:

    • Habitat loss

    • Invasive 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

• 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

Pathogens

• Pathogens: disease causing organisms and viruses

  • Pathogens have the most effect on new habitats or ecosystems with less biodiversity