Chapter 41 –Community Ecology Highlights
Community: A group of populations of different species living close enough to interact.
Interspecific interactions:
Competition - Interspecific competition: -/o Competitive exclusion – 2 species competing for the same limiting resources
cannot coexist permanently in the same place. Inferior competitor will be
o Ecological niche – set of biotic and abiotic resources that an organism uses in its
environment. Niche is organisms “profession” ; habitat is “address”
o Resource partitioning – differentiation of niches that enable similar species to
coexist in a community.
o Fundamental niche: potentially occupied by organism, realized niche – niche
occupied as a result of competition, barnacle study
Predation - +/-, predator/prey
o Predators: feeding adaptations such as senses to identify prey, claws, stingers
o Prey: adaptations to avoid being eaten
 Cryptic coloration – camouflage
 Aposematic coloration – warning colors
 Batesian mimicry – harmless species mimics harmful one
 Mullerian mimicry – two or more unpalatable species resemble each other.
Herbviory - +/- , organism eats parts of a plant or alga.
o Most have specialized senses to detect toxic plants
o Specialized teeth or digestive systems
o Prey: plants, chemical toxins or structures (spines) to protect themselves
Symbiosis – all interactions in which 2 or more species live in direct and intimate contact with
one another.
Parasitism - +/-, parasite: host
o Endoparasites – tapeworms, live internally in host
o Ectoparasites – ticks, liv on external surface of host
Mutualism - +/+, coevolution of related adapations in both species.
o Nitrogen fixation by bacteria in the root nodules of legumes, photosynthesis by
unicellular algae in corals.
Commensalism - +/0, one species benefits while other is neither harmed nor helped.
o Hard to prove, barnacles, cattle egrets
Facilitation - +/+, or 0/+, species have positive effects on the survival and reproduction of other
species without necessarily living in the direct and intimate contact of a symbiosis
 Common in plant species
Species Diversity - variety of different kinds of organisms that make up community
 Species richness – number of different species in community
 Relative abundance – proportion that each species represents of all individuals in
 Invasive species – organisms that become established outside their native range
Trophic structure – feeding relationships between organisms in different trophic levels
 Trophic levels: Food Chain, linked together in Food Webs (figure 41.14)
o Autotrophs – primary producer
o Herbivores – primary consumers
o Carnivores – secondary, tertiary and quaternary consumers
o decomposers
Dominant species in a community – most abundant, highest biomass
Keystone species – not abundant in community, yet exert strong control of community by their
pivotal ecological roles.
Ecosystem engineers – dramatically alter the environment, ex. Beaver
Ecological succession – a disturbed area may be colonized by a variety of species which are in
turn replaced by other species, which are in turn replaced by still other species
Disturbance – an event that changes a community by removing organism from it or
altering resource availability. Ex. Fire, storm, drought
Primary succession – when succession begins in a lifeless area where soil has not yet
formed, ex. Volcano, rubble
Secondary succession – existing community had been cleared by a disturbance that leaves
the soil intact
Human activity is the strongest agent of disturbance today…
Community Ecology and Zoonotic Disease – ¾ of emerging human diseases are caused by
zoonotic pathogens – those transferred to humans from other animals