60 terms

Population and Community Ecology: Distribution and Abundance of Species

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levels of complexity
Individual-Population-Community-Ecosystem-Biosphere
individual
single organism;
survival and reproduction - the unit of natural selection
population
composed of all individuals that belong to the same species and live in a given area at a particular time;
population dynamics (increases and decreases in number of individuals) - the unit of evolution
community
incorporates all of the populations of organisms within a given area;
interactions among species;
often, named for the species that is visually dominant
ecosystem
consists of all of the biotic and abiotic components in a particular location;
flow of energy and matter, such as the cycling of nutrients through a system
biosphere
the largest and most complex system environmental scientists study; incorporates all of the Earth's ecosystems;
movement of air, water, and heat around the globe
population inputs and outputs
inputs: immigration and births increase population size, while outputs: emigration and deaths decrease population size
population ecology
the study of populations in relation to the environment, including environmental influences on population density and distribution, age structure, and variations in population size
population size
N, is the total number of individuals within a defined area at a given time
population density
the number of individuals per unit area (or volume, in the case of aquatic organisms) at a given time;
with population size, this information can be used to estimate whether a species is rare or abundant;
implications for wildlife management and food supply
population distribution
a description of how individuals are distributed with respect to one another - random (no pattern), uniform (evenly spaced), and clumped
population sex ratio
the ratio of males to females within a given population; usually close to 50:50
this information can be used to estimate the number of offspring a population will produce in the next generation
population age structure
a description of how many individuals fit into particular age categories;
this information can be used to estimate how quickly a population can grow
factors that influence population size
density dependent or density independent factors
density-dependent factors
a factor that influences an individual's probability of survival and reproduction in a manner that depends on the size of the population;
example: available food
limiting resource
a resource that a population cannot live without and which occurs in quantities lower than the population would require to increase in size;
as food decreases, for example, so does the size of the population that depends on it;
other examples: water, soil nutrients (plants), nesting sites (animals);
population growth is rapid at low population densities but slow at high population densities
carrying capacity
K, the limit of how many individuals in a population the food supply can sustain
density-independent factors
a factor that has the same effect on an individual's probability of survival and the amount of reproduction at any population size;
examples: hurricanes, floods, fires, volcanic eruptions, extreme heat/cold
population growth models
mathematical equations that can be used to predict population size at any moment in time
growth rate
the number of offspring an individual can produce in a given time period, minus the deaths of the individual or its offspring during the same period
intrinsic growth rate
r, the maximum potential growth of a population under ideal conditions with unlimited resources;
under ideal conditions, the number of deaths decrease - this produces a high population growth rate
exponential growth model
a mathematical equation that tells us that, under ideal conditions, the future size of the population (N(t)) depends on the current size of the population (N), the intrinsic growth rate of the population (r), and the amount of time (t) over which the population grows
j-shaped curve
the shape of the exponential growth model when graphed; when populations are not limited by resources, their growth can be very rapid, as more births occur with each step in time
logistic growth model
describes a population whose growth is initially exponential, but slows as the population approaches the carrying capacity of the environment; used to predict the growth of populations that are subject to density-dependent constraints
s-shaped curve
the shape of the logistic growth model when graphed; if a population starts out small, its growth can be very rapid, but, as the population size nears about one-half of the carrying capacity, its population growth slows and eventually reaches zero
overshoot
when a population becomes larger than the environment's carrying capacity; corrected by die-off
die-off
a rapid decline in a population due to competition for food, and ultimately, death
k-selected species
a species with a low intrinsic growth rate that causes the population to increase slowly until it reaches carrying capacity; small population fluctuations; tends to apply to large organisms that reach reproductive maturity relatively late, produce a few, large offspring, and provide substantial parental care;
examples: elephants, whales, humans
r-selected species
a species with a high intrinsic growth rate, which often leads to population overshoots and die-offs; tends to apply to small organisms that reach reproductive maturity early, reproduce frequently, produce many small offspring, and provide little or no parental care;
examples: house mice, small fish, insects, weedy plant species
survivorship curve
a graph that represents the distinct patterns of species survival as a function of age; three types
type I survivorship curve
k-selected species have high survival rates throughout most of their life span; as they approach old age, however, they start to die in large numbers
type III survivorship curve
r-selected species experience low survivorship early in life, and few individuals reach adulthood
type II survivorship curve
species, such as corals and squirrels, experience a relatively constant decline in survivorship throughout their life span
corridors
a strip of natural habitat that connects separated populations
metapopulations
a group of spatially distinct populations that are connected by occasional movements of individuals between them;
occasional immigrants from larger nearby populations can add to the size of a small population and introduce new genetic diversity - may reduce the risk of extinction
species distribution
determined by the following three factors: 1) the species' fundamental niche - the range of abiotic conditions that it can tolerate; 2) the species' ability to disperse to that area; 3) interactions with other species
species interactions
competition; predation; mutualism; commensalism
community ecology
the study of interactions between species
competition
the struggle of individuals to obtain a limiting resource
competitive exclusion principle (Gause)
states that two species competing for the same limiting resource cannot coexist; competition for a limiting resource may lead to resource partitioning
resource partitioning
a situation in which two species divide a resource, based on differences in their behavior or mophology;
types: temporal, spatial, or morphological;
when two species overlap in their use of a limiting resource, selection favors those individuals of each species whose use of the resource overlaps the least with that of the other species;
over many generations, the two species can evolve to reduce their overlap - example: small-beaked and large-beaked finches
predation
the use of one species as a resource by another species;
types: true predators, herbivores, parasites, and parasitoids;
role: to regulate prey population
true predators
predators that typically kill their prey and consume most of what they kill; example: African lion preys on gazelle, lynx preys on snowshoe hares
herbivores
predators that consume plants as prey; they typically eat only a small fraction of an individual plant without killing it;
example: gazelles of the African plain
parasites
predators that live on or in the organism they consume, referred to as their host; they typically consume only a small fraction of their host - they rarely cause death of their host;
example: tapeworm, pathogens (cause disease in their host), including viruses, bacteria, fungi, protists
parasoids
predators that lay eggs inside other organisms; when the eggs hatch, the larvae slowly consume the host from the inside out, eventually leading to the host's death; example: wasps
mutualism
the third type of interspecific interaction, benefits two interacting species by increasing both species' chances of survival or reproduction;
example: plants and their pollinators (birds, bats, insects) - plants depend on pollinators for their reproduction, and pollinators depend on plants for food
commensalism
a type of relationship in which one species benefits but the other is neither harmed nor helped;
example: birds using trees as perches
symbiotic relationship
a relationship of two species that live in close association with each other; describes commensalism, mutualism, and parasitism
keystone species
a species that plays a role in its community that is far more important than its relative abundance might suggest; may be predators, sources of food, mutualistic species, or providers of some other essential service;
examples: mussel-eating sea stars in the intertidal, sea otters, plants that produce seasonal fruit/nectar, North American beaver
predator-mediated competition
competition in which a predator is instrumental in reducing the abundance of a superior competitor, allowing inferior competitors to persist
ecosystem engineers
a keystone species that creates or maintains a habitat for other species; example: North American beaver - build dams that convert narrow streams into large ponds, creating new habitat for pond-adapted plants and animals
ecological succession
the predictable replacement of one group of species by another group of species over time;
types: primary or secondary succession
primary succession
a type of ecological succession that occurs on surfaces that are initially devoid of soil, such as an abandoned parking lot, newly exposed rock left behind after a glacial retreat, or newly cooled lava
secondary succession
a type of ecological succession that occurs in areas that have been disturbed but have not lost their soil; may follow events such as forest fire or hurricane which remove vegetation but leave the soil mostly intact
pioneer species
species that can colonize new areas rapidly
factors which influence species richness of a community
latitude; time; habitat size; distance from other communities
latitude & species richness
as we move from the equator toward the North or South pole, the number of species declines
time & species richness
the longer a habitat exists, the more colonization, speciation, and extinction can occur; older communities have had more opportunities for speciation
theory of island biogeography
a theory that demonstrates the dual importance of habitat size and distance in determining species richness;
distance matters because many species can disperse short distances, but only a few can disperse long distances - if two islands are the same size, the nearer island should accumulate more species than the farther island because it has a higher rater of immigration by new species