chapter 41 - ecological communities Flashcards
interspecific interactions
-organisms’ interactions with individuals of other species in the community
competition interaction
-minus/minus interaction
-competition for resources that limits the survival and reproduction of both individuals
competitive exclusion
-species who compete for the same limiting resources cannot coexist permanently in the same place
-one species uses resources more efficiently and reproduce more rapidly than the other
-reproductive advantage of one organism eventually leads to local elimination of the other competitor
ecological niche
-the specific set of biotic and abiotic resources that an organism uses in its environment
-can use it to restate competitive exclusion
-competition for resources can cause evolutionary change in populations: evolution by natural selection can result in one of the species using a different set of resources or similar resources at a different time
competitive exclusion restated
-two species cannot compete for the same limiting resources if they share the same niche
resource partitioning
-the differentiation of niches that enables similar species to coexist in a species
-explains how one species can exist within the same ecological community without pushing another to extinction through competition
fundamental niche
-the niche a species could potentially occupy
-competition with other species can cause one species from fully occupying its fundamental niche
realized niche
-the niche a species actually occupies
-after interactions with other species has been taken into account
-what a species is driven into due to competition
character displacement
-the tendency for characteristics to diverge more in sympatric than allopatric species
-sympatric species that compete for resources show differences in body structure and in the resources they use
-closely related species whose populations are sometimes allopatric (geographically separate) and some-times sympatric (geographically overlapping) provide additional evidence for the importance of competition in structuring communities
exploitation
-minus/plus interaction
-individuals of one species benefits by feeding on and harming individuals of another species
-includes predation, herbivory, and parasitism
predation
-predator of one species kills prey of other species
-predator adaptations: acute senses, fangs+claws+poison, fast anda agile
-prey adaptations: cryptic coloration, aposematic/warning coloration, batesian mimicry
herbivory
-herbivore eats part of plant/alga (harming but usually not killing)
-herbivore adaptations: chemical sensory systems, sense of smell for plant examination, specialized teeth or digestive system
-plant adaptations: (can’t run away like animals, obviously) chemical toxins or structures (spines or thorns)
parasitism
-parasite derives nourishment from and thus host
-parasite adaptations: endoparasites live within host’s body, ectoparasite feed on host’s external surface, complex life cycles, change host’s behavior
positive interactions
-at least one individual benefits and neither are harmed
-large effects on ecological communities
-includes mutualism and commensalism
mutualism
-members of both species benefits
-common in nature
-while there may be costs involved in some interactions, the benefits outweigh these costs
commensalism
-individual of one species benefits and the other neither benefits nor is harmed
-also common in nature
species diversity (of a community)
-the variety of different kinds of organisms that make up the community
-a few species can exert strong control on a community’s structure, including number and relative abundance of the species
-two major components: (1) species richness, (2) relative abundance
relative abundance
-component of species diversity
-the proportion each species represents of all individuals in a community
species richness
-component of species diversity
-the number of different species in the community
biomass
-the total mass of all organisms in a habitat
-introduced species
-organisms that humans have moved to regions outside of the species’ native range
-more diverse communities are more resistant to introduced species because these diverse communities capture more resources available in the system, leaving fewer for the introduced species
trophic structure
-the feeding relationships between organisms
-also (in addition to species diversity) what the structure and dynamics of a community depends on
-trophic interactions of a species have a large impact on the structure of entire communities
food chain
-transfer of food energy from its source in plants and autotrophs/primary producers through herbivores/primary consumers to carnivores/secondary/tertiary/quaternary consumers and eventually to decomposers
trophic level
the position an organism occupies in a food chain
food web
-a group of food chains linked together
-food chains are not isolated units that are separate from other feeding relationships in a community
foundation species
-have strong effects on their communities as a result of their large size/high abundance
e.g. trees, desert shrubs, marine algae
-community-wide effects because they provide a habitat or food
-may be competitively dominant: superior in exploiting key resources
keystone species
-not usually abundance in a community
-exert strong control on community structure by ecological role, not their numbers
ecosystem engineers
-species that create or dramatically alter their environment
-can modify the physical environment in ways that create habitats on which other species depend
bottom-up model
-model of community organization
-unidirectional influence from lower to higher trophic levels
-to change community structure of a bottom-up community, biomass needs to be altered at lower trophic levels to allow those changes to propagate up
-e.g. adding mineral nutrients –> plant growth –> higher trophic levels increase in biomass
top-down model
-model of community organization
-predation mainly controls community organization because predators limit herbivores, herbivores limit plants, and plants limit nutrient levels through nutrient uptake
-alternating effects throughout this model
-can be seen in biomanipulation
biomanipulation
-attempt to improve water quality in lakes with high abundance in algae
-alters density of higher-level consumers
disturbance
-influences species diversity and composition
-an event, such as a storm, fire, flood, drought, or human activity
-changes a community by removing organisms from it or altering resource availability
nonequilibrium model
-emphasis on change in communities
-most communities are constantly changing after disturbance
intermediate disturbance hypothesis
-moderate levels of disturbance foster greater species diversity than do high or low levels of disturbance
-high levels of disturbance reduce diversity by creating environmental stresses that exceed the tolerances of many species
-low levels of disturbance can reduce species diversity by allowing competitively dominant species to exclude less competitive ones
-intermediate disturbances foster greater species diversity by opening up habitats for occupation by less competitive species –> rarely create conditions so severe that they exceed the environmental tolerances or recovery rates of potential community members
ecological succession
-a disturbed area may be colonized by a variety of species, which are gradually replaced by other species, and so on
primary sucession
-ecological succession begins in virtually lifeless area
-typically the only life forms are protists and prokaryotes
secondary succession
-recolonization of an area after a major disturbance has removed most but not all of the organisms in a community
evapotranspiration
-the evaporation of water from soil and plants
species-area curve
-all other factors being equal, the larger geographic area of a community, the more species it has because larger areas offer a greater diversity of habitats
pathogens
-disease-causing microorganisms and viruses
-produce clear effects on community structure
zoonotic pathogens
-pathogens that are transferred to humans from other animals
