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 * 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: +/- 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

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: (+/+ 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 (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

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 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 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: 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: disease causing organisms and viruses * Pathogens have the most effect on new habitats or ecosystems with less biodiversity