Concerned with community structure and population interactions Community Ecology Concerned with community structure and population interactions
Interactions Five categories Competition Predation Mutualism Commensalism Parasitism
Competition
Competition Interspecific competition The competition between two or more species for some limiting resource food or nutrients, space, mates, nesting sites Resolutions Competitive exclusion principle (Gause’s principle) Resource partitioning Character displacement Realized niche Competitive interactions between organisms can have a great deal of influence on species evolution
The Competitive Exclusion Principle G.F. Gause-worked with 2 strains of Paramecium -States that two species competing for the same limiting resources cannot coexist in the same place When two species compete, one is likely to be more successful. Cannot coexist if they share the same niche. One species could become extinct or evolve to exploit different resources resource partitioning) Divergence in adaptation is called character displacement. Animation
Ecological Niches The ecological niche Is the total of an organism’s use of the biotic and abiotic resources in its environment The niche concept allows restatement of the competitive exclusion principle Two species cannot coexist in a community if their niches are identical Clip
Resource Partitioning Resource partitioning is the differentiation of niches A. insolitus usually perches on shady branches. A. distichus perches on fence posts and other sunny surfaces. A. distichus A. ricordii A. insolitus A. christophei A. cybotes A. etheridgei A. alinigar That enables similar species to coexist in a community Minimizes competition & maximizes success
Resource Partitioning Resource partitioning is a way in which different species can use the same resource, such as food, without occupying the same physical location at the same point in time. In this example, the different warblers eat the same caterpillar, but they occupy different positions in the tree. Two primarily occupy the area near the trunk, with the others share the edges of the branches, but at different heights. The result is the warblers do not overtly compete for food in the same space.
Character Displacement (niche shift) As a result of resource partitioning. -Divergence in adaptation G. fortis Beak depth (mm) G. fuliginosa Beak depth Los Hermanos Daphne Santa María, San Cristóbal Sympatric populations G. fuliginosa, allopatric G. fortis, allopatric Percentages of individuals in each size class 40 20 8 10 12 14 16 There is a tendency for characteristics to be more divergent in sympatric populations of two species than in allopatric populations of the same two species Speciation: Allopatric-geographic barriers Sympatric- no geo barrier
Niche theory distinguishes between fundamental & realized niches: fundamental = all possible conditions under which population reproduces itself realized niche = the actual niche exhibited in particular time & place
Predation True predator Parasite Parasitoid Herbivore Snowshoe Hare and Canadian Lynx
Camouflage Cryptic coloration -passive defense Cryptic coloration Fur of snowshoe hare is white in winter and brown in summer The larvae of some moths are colored like bird droppings Marking on animals to blend in to background. Lizard
Aposematic coloration (warning coloration) Coloration that warns predators Predators learn to associate color with bad taste or harmful chemical Mimicry Two types Mϋllerian Batesian
Müllerian mimicry Two or more unpalatable species resemble each other (a) Cuckoo bee (b) Yellow jacket
Batesian mimicry A palatable or harmless species mimics an unpalatable or harmful model (a) Hawkmoth larva (b) Green parrot snake
passive defense Spins, thorns, poisons Hiding, fleeing
Community Interactions Symbiosis Predatory-Prey Competition
Symbiosis Mutualism (+/+) Commensalisms (+/o) Parasitism (+/-)
(+/+) Mutualism
Commensalism One species benefits and the other is not affected It is difficult to determine true commensalism because it is difficult to ensure host is not harmed. Ex: Barnacles that attach themselves to the backs of whales
Parasitism (+/-) Relationship in which one species benefits; while harming the other Tomato hornworm covered with cocoons of pupating wasps
Diversity of Species in Ecosystems: Species Diversity: variety of different organisms in a community…two components Species Richness Number of different species in a community Relative Abundance Proportion each species represents of all individuals in the community
Higher diversity communities are more resistant to invasive species Higher diversity communities are more resistant to invasive species. These are organisms that have become established outside of the native range. Diverse communities are better at partitioning resources and disallow the establishment of invasive species.
DOMINANT SPECIES KEYSTONE SPECIES Species that is the most abundant or collectively occupies the most biomass. These species become “dominant” due to: -being competitively superior -avoid predation** -avoid disease** **this may be why invasive species can thrive, natural parasites and predators may not attack invasives. KEYSTONE SPECIES Species that is not particularly abundant but exert strong control on community structure because of a pivotal niche. Ex/ in tidal pools, starfish are important in maintaining the diversity by being a keystone predator and not allowing any one organism to become a dominant species.
Review of Community Interactions
Ecological Succession
Ecological Succession
Ecological Succession Primary succession Occurs where no soil exists when succession begins Starts with pioneer species (lichens & mosses)
Ecological Succession Secondary succession Begins in an area where soil remains after a disturbance takes place where a community has been removed, e.g., in a plowed field or a clearcut forest
(a) Soon after fire. As this photo taken soon after the fire shows, the burn left a patchy landscape. Note the unburned trees in the distance. ( b) One year after fire. This photo of the same general area taken the following year indicates how rapidly the community began to recover. A variety of herbaceous plants, different from those in the former forest, cover the ground.