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

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