Chapter 52: Community Ecology
52.1 Species Interactions
The fitness of an individual is defined as its ability to produce viable, fertile offspring.
The four common types of interactions:
Commensalism occurs when one species benefits but the other species is unaffected.
Competition occurs when individuals use the same resources-resulting in lower fitness for both.
Consumption (including herbivory, predation, and parasitism) occurs when one organism eats or absorbs nutrients from another.
The interaction increases the consumer’s fitness but decreases the victim’s fitness.
Mutualism occurs when two species interact in a way that confers fitness benefits to both.
The competition that occurs between members of the same species is called intraspecific competition.
Interspecific competition occurs when individuals from different species use the same resources.
Note that species may compete directly for the same resources, such as a lion fighting off a hyena to control access to a zebra carcass.
Species may also compete indirectly for the same resources, such as when a finch consumes all of the available seeds on a bush, leaving no seeds for species visiting the bush later.
Early work on interspecific competition focused on the concept of the niche，the range of resources that the species is able to use, or the range of conditions it can tolerate.
A fundamental niche is the total theoretical range of environmental conditions that a species can tolerate.
A realized niche is the portion of the fundamental niche that a species actually occupies, given limiting factors such as competition with other species.
An evolutionαry change in resource use, caused by competition over generations, is called niche differentiation or resource partitioning.
The evolutionary change that occurs in species traits, and that enables species to exploit different resources, is called character displacement.
Character displacement makes niche differentiation possible.
In agriculture and forestry, the use of predators, herbivores, and parasites as biocontrol agents is a key part of integrated pest management: strategies to maximize crop and forest productivity while using a minimum of insecticides or other types of potentially harmful compounds.
When predators and prey, herbivores and plants, or parasites and hosts interact over time, a coevolutionary arms race often results-a repeating cycle of reciprocal adaptation.
52.2 Community Structure
You might also be familiar with linking consumption interactions sequentially into a food chain such as “aspen is eaten by elk, and elk are eaten by wolves.”
Overlapping food chains can then be combined into a food web, a summary of some or all of the consumption interactions in a community.
A keystone species has a much greater impact on the distribution and abundance of the surrounding species than its abundance and total biomass would suggest.
52.3 Community Dynamics
A disturbance is any strong, short-lived disruption to a community that changes the distribution of living and/or nonliving resources.
The recovery that follows is called succession.
Primary succession occurs when a disturbance removes the soil and its organisms as well as organisms that live above the soil surface.
Secondary succession occurs when a disturbance removes some or all of the organisms from an area but leaves the soil intact, including the seeds and microorganisms within.
Fire and logging are examples of disturbances that initiate secondary succession on land.
Pioneering species tend to have “weedy” life histories.
In ecology, a weed is a plant that is adapted for growth in disturbed soils.
Chapter 52: Community Ecology
52.1 Species Interactions
The fitness of an individual is defined as its ability to produce viable, fertile offspring.
The four common types of interactions:
Commensalism occurs when one species benefits but the other species is unaffected.
Competition occurs when individuals use the same resources-resulting in lower fitness for both.
Consumption (including herbivory, predation, and parasitism) occurs when one organism eats or absorbs nutrients from another.
The interaction increases the consumer’s fitness but decreases the victim’s fitness.
Mutualism occurs when two species interact in a way that confers fitness benefits to both.
The competition that occurs between members of the same species is called intraspecific competition.
Interspecific competition occurs when individuals from different species use the same resources.
Note that species may compete directly for the same resources, such as a lion fighting off a hyena to control access to a zebra carcass.
Species may also compete indirectly for the same resources, such as when a finch consumes all of the available seeds on a bush, leaving no seeds for species visiting the bush later.
Early work on interspecific competition focused on the concept of the niche，the range of resources that the species is able to use, or the range of conditions it can tolerate.
A fundamental niche is the total theoretical range of environmental conditions that a species can tolerate.
A realized niche is the portion of the fundamental niche that a species actually occupies, given limiting factors such as competition with other species.
An evolutionαry change in resource use, caused by competition over generations, is called niche differentiation or resource partitioning.
The evolutionary change that occurs in species traits, and that enables species to exploit different resources, is called character displacement.
Character displacement makes niche differentiation possible.
In agriculture and forestry, the use of predators, herbivores, and parasites as biocontrol agents is a key part of integrated pest management: strategies to maximize crop and forest productivity while using a minimum of insecticides or other types of potentially harmful compounds.
When predators and prey, herbivores and plants, or parasites and hosts interact over time, a coevolutionary arms race often results-a repeating cycle of reciprocal adaptation.
52.2 Community Structure
You might also be familiar with linking consumption interactions sequentially into a food chain such as “aspen is eaten by elk, and elk are eaten by wolves.”
Overlapping food chains can then be combined into a food web, a summary of some or all of the consumption interactions in a community.
A keystone species has a much greater impact on the distribution and abundance of the surrounding species than its abundance and total biomass would suggest.
52.3 Community Dynamics
A disturbance is any strong, short-lived disruption to a community that changes the distribution of living and/or nonliving resources.
The recovery that follows is called succession.
Primary succession occurs when a disturbance removes the soil and its organisms as well as organisms that live above the soil surface.
Secondary succession occurs when a disturbance removes some or all of the organisms from an area but leaves the soil intact, including the seeds and microorganisms within.
Fire and logging are examples of disturbances that initiate secondary succession on land.
Pioneering species tend to have “weedy” life histories.
In ecology, a weed is a plant that is adapted for growth in disturbed soils.
