Chapter 18 Flashcards
Memorize all. (43 cards)
Communities are often categorized by…
their dominant organisms or by physical conditions that affect the distribution of species.
Ecotone
a boundary created by sharp changes in environmental conditions over a relatively short distance, accompanied by a major change in the composition of species.
Ecotones support a large number of species, including those from adjoining habitats, and species specifically adapted to the ecotone.
Aquatic systems are often categorized by
physical characteristics (e.g., stream or lake communities) or by dominant organisms (e.g., coral reef communities).
Communities are often categorized by
their dominant organisms or by physical conditions that affect the distribution of species.
Line-transect surveys
can demonstrate the existence of an ecotone.
Sharp changes in the distribution of species should occur across the ecotone.
Interdependent communities
communities in which species depend on each other to exist.
Independent communities
communities in which species do not depend on each other to exist.
Plant biologist Frederic Clements proposed
most communities are interdependent and act as superorganisms.
Plant biologist Henry Gleason proposed
that most communities consist of species with independent distributions.
If species distributions are independent, they should depend only on __________ _________ _______; there should be gradual changes in species along a line transect.
individual habitat requirements
If species are interdependent, removing a species should cause other species to ___________
decline
if species are independent, removing a species should cause _________ or _________ changes in other species’ fitness.
neutral or positive
Species living under harsh environmental conditions (e.g., high elevation) frequently exhibit ______________.
interdependence
Species richness
the number of species in a community.
Relative abundance
the proportion of individuals in a community represented by each species.
Log-normal distribution
a normal, or bell-shaped, distribution that uses a logarithmic scale on the x-axis.
Rank-abundance curves
a curve that plots the relative abundance of each species in a community in rank order from the most abundant species to the least abundant species.
To plot a rank-abundance curve, rank each species in terms of its abundance; the most abundant species receives a rank of 1, the next most abundant species receives a rank of 2, etc.
Species evenness
a comparison of the relative abundance of each species in a community.
most commonly observed relationship between diversity and productivity
Across studies of vertebrates and invertebrates in aquatic and terrestrial systems, a hump-shaped curve.
his indicates that a site with medium productivity has a higher species richness than sites with either low or high productivity.
This suggests that light limitation by dominant plant species _________ ________ _________ in fertilized plant communities.
reduces species richness
Keystone species
a species that substantially affects the structure of communities, although species might not be particularly numerous.
Removal of a keystone species can cause a community to collapse.
Ecosystem engineers
are keystones species that affect communities by influencing the structure of a habitat.
Intermediate disturbance hypothesis
the hypothesis that more species are present in a community that experiences occasional disturbances than in a community with either frequent or rare disturbances.
Food chain
a linear representation of how different species in a community feed on each other.