TR

Community Ecology, Biodiversity, and Disruptions

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