chap 15- nature of communities

• group of interacting species at same place and time
• synergistics: interactions make communities into something more than the sum of parts
• considered to be fundamental unit of landscape
• often classified by physical or biological characteristics

• Taxonomic affinity: "birds"
• Guild: group of species using same resources "birds, bees, and bats are all pollen-eating animals"
• Functional Group: includes species that function in a particular way but do not necessarily use the same resources misquetos and aphids
• Food Web: based on trophic, energentic, interactions

• organzed by tropic levels- group of species that have similar wayto obtain energy
• primary producer: autotrophs
• primary consumers: herbivores
• secondary consumers: carnivores
• tertiary consumers: carnivores
• does not tell about strength of interaction

• used to describe both trophic and non-trophic interactions among species
• omnivores: feed on more than one trophic level
• horitontal interactions: competition and positive interactions

• set of characteristics that shape a community
• include species diversity and species composition

• a measure that combines relative number of species to relative abundance
• Shannon Index: calculated number showing diversity lowest 0 can go to infinity, the higher the value the more diversity

number of species

tells commonness or rarity of species

describe the diversity of important ecological entities that span multiple spatial scales, genes to species to communities

plots proportional abundance of each species to the others in rank order from most to least abundant

• calculated by plotting species richness as a function of the sampling effort
• theoretically the more sampling done the line levels off revealing fewer or no new species

identity of the species present in the community

occur between 2 species and include trophic and non-trophic interactions

relationship between 2 species is mediated by a 3rd or more species

• rate of consumption at one level results in a change in species abundance or composition at lower trophic levels
• kelp forest, urchins and otters

• consumer is indirectly facilitated by a positive interaction between its prey and another species,
• juncus helped iva plant grow in turn helping aphid population

• competitive interactions among multiple species in which every species negatively interacts with every other species
• circular web rather than linear

• effect of one species on the abundance of another
• can be measured experimentally by removing one species(interactor species) from the community and looking at the effect on the other species(target species)
• if removal of interactor resluts in large decrease in target species, interaction is strong and positive
• if the abundance of the target increase the interactor species has srong negative effect

• aka foundation species
• large or abundant species or biomass in community, usually trees, provide habitat or food for other species

are able to create. modify, or maintain physical habitat for themselves and other species

• large effect on community not because of thier abundance but because of the roles they play
• influence community structure indirectly , by trophic means

changeable under different enviromental conditions