Ecology PDF

Community Community: a group of organisms that live together at the same place and time and · interact directly or indirectly A community includes all of the organisms present – animals, plants, fungi, bacteria, etc. diff means organisms...

Community Community: a group of organisms that live together at the same place and time and · interact directly or indirectly A community includes all of the organisms present – animals, plants, fungi, bacteria, etc. diff means organisms relationships (niches) 22 Forest communities across Canada 23  Forest communities across Canada ↑ where we live FIGURE 9.1 24  Community organization Changes in environmental factors, called “environmental gradients”, often correspond to community changes Gradual ecotone from Often there is a gradual spruce to dwarf forest transition from one community to another Sometimes change is abrupt Such transition zones are called ecotones Sharp ecotone from FIGURE 9.3 grasslands to forest 25  Community unit concept Frederick Clements proposed the community - unit concept of - communities: A community is a highly organized and closely integrated entity that is composed of mutually 6 interdependent species EX birds beingthat are co-adapted on the dependent prey scared ↳ make flowers outofthew as Frederick Clements, plant (aka organismal concept) sexually pollinators come and reward nectar and help reproduce ecologist (1874-1945) 26  Continuum concept Henry Gleason proposed the continuum concept - of communities: Communities are a coincidental assemblage - of species that have similar environmental - requirements - - biotic and abiotic factors - (aka individualistic concept) Henry Gleason, plant ecologist (1882-1975) 27  Concepts of communities Clements’ community unit concept predicts ecotone Z discrete community types with sharp ecotones more along line gradient each rep diff species and how often it is found there Gleason’s continuum each of line one rep distribution particular speciesalonggradients concept predicts continuous variation NO SHARP ECOTONES FIGURE 9.4 28  Concepts of communities Particular species of flowering plants in two different states Data on plant communities in western U.S. revealed continuous, non-discrete distribution patterns along gradients of environmental factors These data support Gleason’s continuum concept - Oregon Arizona FIGURE 9.5 29  Synthesis empirical data supports concept > - Most ecologists favour Gleason’s continuum concept of communities But Clements’ community unit concept is also accepted, and is useful: Discrete community units are pragmatic for applied disciplines such as forestry 30  Functional organization Communities are also organized by the functional role species play Communities can be studied based on their trophic position: autotrophs herbivores carnivores detritivores 32  Functional organization Additionally, communities can be studied based on the way organisms use resources A guild is a group of organisms that use similar resources not the necessarily same species Example: hummingbirds, bats, and insects that feed on nectar and pollen are a “floral-visiting guild” 33  Interactions Interactions between organisms is the key subject area in community ecology These interactions influence the presence and abundance of species 34  Types of interactions Herbivory Predation Competition Disease Symbiosis Mutualism Parasitism Commensalism all areas of study 35  can completely change an Herbivory ecosystem destroy > - all spruce trees Herbivores can have a FOOD major influence on community composition Example: larvae of spruce budworm eat leaves of fir and spruce; they are always present U/LL ALL SPRUCE TREES at low densities; sometimes, spruce budworms irrupt and kill most mature trees in affected stands 36  Predation Predators have an influence on community structure: they reduce herbivore populations, which can lead to SPRUCE improved plant growth WORMS Example: boreal- ↑ breeding birds eat insects and other invertebrates - keep population under control 37  competition at every stage Competition wowCE ⑨ * Resources in limited supply are competed for Plants compete for light, nutrients, water, etc. Animals compete for food, territory, nesting locations, etc. Competitive ability strongly influences a species’ presence and abundance 38  Disease Disease can reduce population size Example: Sea urchin irrupt and overgraze kelp in intertidal zones; warm water induces a potent disease in urchins eat help that makes healthy all compete access and close contact ↳ disease ↳ help returns 39  Symbiosis Symbiosis is an acadia ant on bullhorn acacia intimate relationship OBLIGATE 2 ant live on tree between two organisms Obligate relationships are those where the organisms cannot live apart 40  Symbiosis: mutualism Mutualism: both partners benefit Obligate mutualisms are quite common don't both on need be to obligate eachother Examples: Many plants and pollinators live in mutualistic relationships; the plant provides glucose to the pollinator through nectar; the pollinator disperses the plant’s seeds 41  Symbiosis: parasitism tree pain - Parasitism: one of the partner benefits, and the other suffers Example: strangler figs parasitize the vertical structure of host trees to access sunlight use host to get higher 42  Symbiosis: commensalism Commensalism: one of the partners benefits, and the other is unharmed plant grows on other plant Example: epiphytic - plants, such as lichens, are supported on high surfaces of trees and the host tree is not usually affected 43 Parasitism, Mutualism, or Commensalism? OBLIGATE MUTUALISM MUTUALISM Acacia ants & acacia trees Rhizobium bacteria & clover MUTUALISM > - eat insects parasites' no cost - Large ungulates & egrets Antbirds & army ants 44