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Chapter 26: Community Ecology (Concepts (community restoration: work and…
Chapter 26: Community Ecology
Concepts
Community
: a group of species that occur together at the same time and place
climax community
: a community in which the variety and relative abundance of organisms remain the same for many years; typically result of succession
succession
: a more-or-less predictable sequence of changes over time of the species that occur in an area
community restoration
: work and projects that are carried out with the objective of altering a group of organisms back to a more natural state
Ex: Reintroducing wolves into various areas or by removing dams from rivers
habitat loss
: the result of any of several processes that cause a habitat to be unable to support the species diversity it had when in a natural state
Ex: Clearing land for agriculture, cities, and mining all contribute to habitat loss, as does climate change
habitat fragmentation
: the conversion of a large habitat into several smaller ones as various regions of it become uninhabitable for the organism being considered
Ex: Building canals or logging strips of forest are examples of activities that fragment habitats
Diversity
Diversity and Scale
checklist
: in studies of ecology and biodiversity, a checklist is simple list of all the species known to exist in a particular area; often prepared for parks and nature preserves
scale
- Larger areas are more diverse than smaller ones.
species-area relationship
: the relationship between the size of an area and the number of species present; often, a small area has fewer species than does a larger area
species abundance distribution
: a plot of the number of species in a region into various abundance classes; a common result is that a few species are extremely common, the rest are each rather rare
Diversity and Latitude
Predator-Prey Interactions
Predator Selection Among Multiple Prey
optimal foraging theory
: examination of interactions between the following factors in an attempt to understand why animals select certain prey over others
The decision by the predator to attack an individual once it has been encountered.
The probability that an attacked prey item will be successfully eaten.
The probability that a particular prey individual will be encountered.
optimal diet model
: contains four predictions
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If the high-yield prey become sufficiently scarce, then the predator would be more successful by broadening its diet to include prey that lower in energy if they are abundant and easy to handle.
Some prey items will always be eaten if they are encountered, others will never be eaten if easy to obtain
Ex: If the edible parts are not worth the trouble of overcoming the plant's defenses.
Predators should prefer whichever prey yields the most energy per unit of handling time.
Less profitable prey will be ignored if more profitable prey is available.
Competition Between Species
exploitation competition
: resource competition occurs when the organisms actually consume a shared resource, thus making it less available for other organisms
interference competition
: one organism restricts another organism's access to resources even though the first might not be using it
invasive
: a species that can increase from very low population density even if one or several competitors are present
resource
: any substance or factor that can lead to increased growth rates as its availability is increased and that is consumed by an organism
One Predator, One Prey
functional response
: in predator-prey relationships, functional response refers to the predator's feeding rate and it's handling time
prey-dependent
: feeding rate will be faster if there are more prey individuals available, so a predator's functional response is dependent on prey density
zero growth isocline
: graph of predator-prey relationships
ZGI- the line that indicates the sizes of predator and prey populations that are stable
If the predator population is sparser than that of the line, the prey population will increase
If predator populations are greater than the line, the prey population decreases.
paradox of enrichment
: the reduction or loss of a population from a habitat as a result of that habitat being altered to benefit the population
Mechanism includes a temporary increase in the population, followed by either a harmful increase in the predators of the population or a harmful overconsumption of a limited resource.
maximum sustained yield
: amount of an organism's population that can be harvested without causing the population to decrease
Because many organisms have a sigmoidal growth curve (they increase more slowly as populations become overcrowded), harvesting the proper amount from an overcrowded population should maintain the population at its most productive level.
fixed effort harvesting
: a technique that attempts to limit damage to a species by automatically decreasing harvests whenever a resource is in short supply or is endangered
Ex: Effort may be fixed by allowing hunting for only a particular number of days
Ex: Or by limiting the number of fishing boats.
fixed quota harvesting
: a technique that attempts to limit damage to a species by setting limits on the amount of the species can be harvested.
Ex: Individual hunters are typically allowed to kill only one deer each
Apparent Competition
: one predator may prey on several species
If one of the prey species increases in abundance for any reason, that may lead to an increase in the predator population, resulting in more predation on all prey species.
The increase of one prey species may cause the decrease in other prey species, which appears to be the result of competition but is not.
Metapopulations in Patchy Environments
sink habitat
: a habitat that is so poor that it cannot support a population of a particular species indefinitely
The species is maintained only by migration from nearby richer habitats (source habitats)
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fugitive species
: a species that survives by colonizing new patches, flourishing temporarily, and then colonizing more patches before it dies out in old ones
Ex: Weeds
source habitat
: a habitat that can support a population of a particular species indefinitely
Seeds, spores, or other propagules become dispersed from source habitats to poorer sink habitats.
assisted dispersal
: the artificial transport of organisms by people with the objective of introducing those organisms into new areas, thus increasing their range and reducing the risk of extinction
metapopulation
: a population that consists of several local populations interconnected by migration and gene flow between the patches
Interconnectedness of Species: Food Chains and Food Webs
food web
: various organisms eat or decompose others, and these in turn are consumed
food chain
: a set of organisms in which some are primary producers, others are primary consumers (which consume the primary producers) and still others are secondary consumers
keystone species
: a species that dramatically affects the structure of its community, having an impact out of proportion to its size or the number of individuals present
energy flow web
: various organisms eat or decompose others, and these in turn are consumed
Because some organisms consume the same prey, and in turn each is consumed by various other organisms, energy flows through the community in a weblike pattern.
Beneficial Interactions Between Species
nurse plants:
the presence of some plants creates conditions that allow other plants to become established
Ex: May provide shade, camouflage, or protection to the seedlings of the second plant.
primary succession
: the establishment of plants in a habitat that has been devoid of them
Ex: The establishment of the first plants on the new land that is available as a glacier retreats or on the barren land produced by a volcano
facilitation
: the situation in which the presence of one's species provides benefit to another although the first species is neither helped nor harmed by the situation
mutualism
: an interaction of two species in which both species benefit
