Chapter 55 Community Ecology

Biology 101

Tri-County Technical College

Pendleton, SC

Some Key Terms

• Population = localized group of individuals belonging to the same species

• Community = assemblage of species close enough for potential interaction

• Habitat = place or environment where an organism naturally or normally lives and grows

• Niche = habitat supplying the factors necessary for existence of organism OR ecological role of an organism in a community (especially in regard to food consumption)

More Key Terms

• Resource = anything directly used by organism that can potentially lead to growth of population and whose availability is reduced when it is used– Food and space

• Limiting resource = resource whose supply is LESS than the demand made upon it by organisms– Generally are subject to depletion and

regenerate slowly

Symbiosis

• Defined as “living together”

• Predator-Prey– Predator is organism that kills and eats

• animals by animals/eating of plants

– Prey (host) is organism consumed as energy source

– Serves as agent of natural selection as well as for mortality

Predator-Prey Visual

Symbiosis II• Parasitism describes organism that lives on or in a

host– Not wise to kill the host– Microparasites (viruses, bacteria, & protists)– Very short generation times & host may harbor 1000s

to millions – Best defined as one benefits and one is harmed

• Competition = use of same resource by two or more species when resource is present in insufficient supply for combined needs of both– Both are harmed by competition

Symbiosis III

• Mutualism = both participants BENEFIT

• Commensalism = occurs when one participant benefits and the other is unaffected (neither benefits or is harmed)

• Amensalism = occurs when one participant is harmed but the other is unaffected

Species Richness and more…• Species richness of a community describes

the number of species that live there• Keystone species = species whose

influences on ecological communities ARE greater than would be expected– Influences species richness, flow of energy, and

materials in an ecosystem

• Succession = sequence of change in species composition of a community

Competition• Intraspecific competition defines competition

among individuals of same species– May result in reduced growth & reproductive rates for

some, exclude some from better habitats, and cause death in others

• Interspecific competition defines competition among individuals of different species

• Same results as intraspecific but may keep entire species out of habitats where they cannot compete successfully in phenomenon called competitive exclusion

Mutualism• Most complex and important symbiosis

between members of different kingdoms or domains

• Mycorrhizae, lichens, animals & protists (termites and corals)

• Animal-animal (ants and aphids and the milking process)

• Plants-animal (trees and ants; angiosperms and pollen)

…and finally, brethen

• Commensalism (cattle egrets and grazing animals)

• Amensalisms are widespread and important in nature

• Mammals and watering holes; trees dropping leaves and branches

A form of flattery…

• Mimicry is an evolved resemblance to some inedible or unpalatable item

• Batesian mimicry = palatable species mimics an unpalatable or noxious one– Spiders that mimic wasps; insects that mimic

bees or wasps– Works because predator that captures

individual of unpalatable/noxious species learns to avoid any prey of similar appearance

Mimicry II

• Mullerian mimicry = convergence over evolutionary time in appearance of two or more unpalatable species

• All species benefit when inexperienced predators eat individuals of any species because predators learn all species of similar appearance are unpalatable

• Tropical butterflies/bees and wasps

Plant Defenses• Tough leaves, hairs, spines to reduce predation are

physical defenses• Most plant tissue also contains defensive

chemicals called secondary compounds• Are of two general types: acute toxins and

digestibility-reducing compounds• Acute toxins disrupt herbivore metabolism

– nicotine interferes with nerve impulse transmission

– hallucinogens cause seriously distorted view of environment

Defenses II– Imitate insect hormones and prevent insects

from completing metamorphosis– Unusual amino acids that become incorporated

into herbivore proteins and interfere with their functioning

– Other toxins defend against viruses/bacteria

• Digestibility-reducing compounds make plant tissue more difficult to digest

Defenses III– Most common are tannins which are present in

leaves of some herbaceous and most woody plants

– When released by grazing, tannin binds to proteins in leaf and to herbivore digestive enzymes reducing ability of herbivore to extract proteins from leaves

– Why eat it if one cannot get any benefit from it?– Could continue, but….

Succession• Succession = sequence of change in species

composition of a community• Primary succession = establishment of organisms

on newly available sites that previously had NO organisms– retreat of glacier; new volcanic island

• Secondary succession = organisms reestablish themselves on disturbed sites where some organisms survived the disturbance

Succession and more– fires, earthquakes, tidal waves– text gives decomposition of dead bodies of

plants and animals

• Climax community = relatively stable ecological stage or community (especially of plants) that is achieved through successful adjustment to an environment

• Especially applicable to final stage in ecological succession

The love buzz…