Ch 53 – Community Ecology

What is a community? A group of populations of different species living close enough to interact

1. Interspecific interactions Interspecific – between species Can be: – Positive (+) – Negative (-) – Neutral (0) for each species

Interspecific competition Competition (-/-) Result of resources in short supply Competitive exclusion principle- – Two species competing for the same limiting resources cannot coexist. Eventually one will have a selective advantage that will eliminate the other.

Resource partitioning Differentiation of niches that allow similar species to coexist in a community A. distichus perches on fence posts and other sunny surfaces. A. insolitus usually perches on shady branches. A. ricordii A. aliniger A. insolitus A. distichus A. christophei A. cybotes A. etheridgei

Niche Ecological niche – the sum total of a species’ use of the biotic and abiotic resources in its environment Fundamental niche – the niche potentially occupied by a species Realized niche – the portion of the fundamental niche the species actually occupies

EXPERIMENT Chthamalus Balanus realized niche Chthamalus realized niche High tide Low tide High tide Chthamalus fundamental niche RESULTS Ocean For example, the presence of one barnacle species limits the realized niche of another barnacle species

Predation Predator eats prey (+/-) Predator adaptations: – Acute senses to locate and identify prey Many have forward facing eyes & ears (i.e. fox) – Adaptations to help catch & subdue prey: Stingers, teeth, fangs, poisons, etc.

Prey defense Cryptic coloration camouflage Batesian mimicry Unharmful mimics harmful Aposematic coloration warning coloration Mullerian mimicry 2 unpalatable species mimic each other Behavioral defenses

Herbivory Herbivore eats part of plant or alga (+/-) Animal – distinguish non-toxic from toxic plants Plant – defense through toxins, spines, thorns

Symbiosis When individuals of two species live in direct contact with each other Parasitism – parasite gets nourishment from host (+/-) Mutualism – interspecific interaction that benefits both species (+/+) Commensalism – benefits one species, neither helps nor harms other species (+/0)

Symbiotic relationships – blind shrimp & goby: shows/animal-planet-presents/videos/top-10- odd-animal-couples-shrimp-a-goby.htm shows/animal-planet-presents/videos/top-10- odd-animal-couples-shrimp-a-goby.htm

2. Communities are characterized by Diversity & trophic structure Species diversity – Species richness – number of species relative abundance – how common or rare species is Dominant species – have the highest biomass, or are most abundant Keystone species – exert strong control on community structure by their ecological roles or niches (not necessarily the most abundant)

Trophic structure The feeding relationships among organisms in a community Trophic levels – the links in the trophic structure of a community Food chains- what eats what Food webs – two or more food chains connected

3. Disturbance and community structure Disturbance – an event that damages a community Natural or human activities Intermediate disturbance hypothesis – Moderate levels of disturbance create conditions that foster greater species diversity (vs. High or Low levels of disturbance)

Ecological succession Transitions in species composition over ecological time Primary succession – Occurs where soil has not yet formed Secondary succession – Occurs where existing community cleared but soil is intact

Mt. St. Helen’s T2Q T2Q xLY xLY Yellowstone Forest Fire succession onRo onRo

4. Biogeographic factors affecting community diversity Two key factors: Latitude of community – More abundant & diverse life in tropics vs. poles – Area of the community Larger the geographic area of a community, the more species

Island biogeography Two factors: Size of island – the greater the size, the higher the immigration rates, lower rates of extinction Distance from mainland – rate of immigration falls, extinction rates increase

IslandBioGeography.html IslandBioGeography.html