Flashcards in Community Ecology Deck (118):
An assemblage of plant and animal populations that live in a particular area or habitat.
characterizes communities. Populations of the various species in a community utilize, decompose, compete with, and alter the fates of each other. Together they form a system with its own emergent properties.
Seeks to explain the underlying mechanisms that create, maintain, and determine the fate of biological communities. Typically, patterns are documented by observation, and used to generate hypotheses about processes, which are not always easy to observe directly.
Community ecology hypotheses are always tested experimentally
False, they can involve special observations
Examples include vegetation zonation, species lists, seasonal distribution of activity, and association of certain species
Examples include processes-herbivory, competition, predation risk, nutrient availability, patterns of disturbance, energy flow, history, and evolution
is the way species are distributed relative to each other.
Some species provide a framework that creates habitats for other species. These species, in turn create habitats for others, etc.
An example of this is trees in a rainforest stratifying into several different layers, each with a habitat of a distinct collection of species
The time of the appearance and activity of species
Ex: arctic tundra, seasonal ponds, desert plants and animals that emerge after seasonal rains
The number of species in a community. Clearly, the number of species we can observe is function of the area of the sample. It also is a function of who is looking. Thus, it is sensitive to sampling procedure
The number of species in the community, and their relative abundances.
Species are not equally abundant, some species occur in large percentage of samples, others are poorly represented.
Some communities, such as tropical rainforests, are much more diverse than others, such as the great basin desert.
Species Diversity is often expressed using Simpson’s diversity index:
the predictable change in species over time, as each new set of species modifies the environment to enable the establishment of other species, is virtually ubiquitous.
A sphagnum bog community may persist for only a few decades before the process of ecological succession changes transform it into the surrounding Black Spruce Forest
A forest fire may destroy a large area of trees, clearing the way for a meadow. Eventually, the trees take over and the meadow is replaced.
Lava flows in eventually weather, crack, and allow the establishment of vegetation. Over time this vegetation allows a soil to form, and ultimately, forest.
creates opportunities for new species to invade an area and establish themselves.
These species modify the environment, and create opportunities for other species to invade, The new species eventually displace the original ones
Eventually, the new species, in turn modify the environment enough to allow a new series of invaders, which ultimately replace them, etc
events such as floods, fire, droughts, overgrazing, and human activity that damage communities, remove organisms from them, and alter resource availability.
The best invaders have good dispersal powers and many offspring, but they are often not the best competitors in the long run
Disturbance of a community is usually followed by recovery, called?
This sequence is driven by the interactions among dispersal, ecological tolerances, and competitive ability.
The sequence of species on newly exposed landforms that have not previously been influenced by a community, e.g., areas exposed by glacial retreat.
occurs in cases which vegetation of an area has been partially or completely removed, but where soil, seeds, and spores remain
Early in succession, species are generally excellent dispersers and good at tolerating harsh environments, but not the best interspecific competitors
As ecological succession progresses, they are replaced with species which are superior competitors, (but not as good at dispersing and more specialized to deal with the microenvironments created by other species likely to be present with them
Early species modify their environment in such a way as to make it possible for the next round of species. These, in turn, make their own replacement by superior competitors possible.
is a more or less permanent and final stage of a particular succession, often characteristic of a restricted area.
Climax communities are characterized by..
Slow rates of change (think redwood forests)
They are dominated by species that are tolerant of....
Competition for resources
Why are climax communities so rare?
Succession takes a long time, and the odds that disturbance will occur is high
Do communities work like an integrated machine, in a predictable way (Clements)? Or, do they depend upon random events (Gleason)
Gleason was right, after disturbances communities often never reach former state
A glacier retreated over 100km in Alaska, and three different successional patterns are occurring at once. This does not match other parts of Alaska. Who does this support?
True False: Disturbance and nonequilibrium are abnormal for most communties
Communities usually are in a state of recovery from disturbance
An area of habitat may form a patchwork of communities, each at different stages of ecological succession. Thus, disturbance and recovery potentially enable much greater biodiversity than is possible without disturbance
Do communities have a tightly prescribed organization and composition, or are they merely a loose assemblage of species?
Unclear, yet the 12 pond experiment supported that their composition is unstable and variable
transfer of energy: i.e., eating, decomposing, obtaining energy via photosynthesis
In other words, the hierarchy of feeding in a community
For every community, a diagram of trophic interactions is called
-Energy flows from the bottom to the top
One pattern through a food web
An organism’s habitat, the resources it uses, and its way of making a living, within the context of a community
Very important in community ecology, yet it remains controversial because they are difficult or impossible to observe directly.
This is reflected by an organisms place in a food web: ie., what it eats, what it competes with, what eats it.
Each organism has the potential to create this for others
modifies the environment in such a way that other organisms are able to live, in other cases, the keystone species is a predator that maintains diversity at a certain trophic level. Sometimes, they are mutualists, or “engineers
This keystone species preys upon sea urchins, allowing kelp forests to become established
California Sea Otters
This keystone species prevents the establishment of dense mussel beds, allowing other species to colonize rocks on the Pacific Coast.
This keystone species disperses in salt water. They take root and form a dense forest in saltwater shallows, allowing other species to thrive
At certain times of year, this keystone species is the sole source of food for honeyeaters, which in turn, are the pollinators for many other species of plants in Western Australia.
The Acorn Banksia
Species at one trophic level influence species at other levels; the addition or subtraction of species affects the entire food web. Can be positive or negative for certain species
True/False: Most biological communities have both top down and bottom up effects on their structure and composition
Fish affecting decreasing the amount of zooplankton (herbivores) and thereby increasing the amount of algae (producer) is an example of
Top down effect
occurs when organisms in the same community seek the same limiting resource. This resource may be prey, water, light, nutrients, nest sites, etc.
Competition among members of the same species
Competition among individuals of different species
True/False: Individuals experience mostly intraspecific OR interspecific competition
False, they experience varying degrees of both
occurs when individuals use the same limiting resource or resources, thus depleting the amount available to others.
occurs when individuals interfere with the foraging, survival, or reproduction of others, or directly prevent their physical establishment in a portion of a habitat.
The confused flour beetle, Triboleum confusum, and the red flour beetle, Triboleum castaneum cannibalize the eggs of their own species as well as the other, thus interfering with the survival of potential competitors. What is this an example of?
In mixed species cultures, one species always excludes the other. Which species prevails depends upon environmental conditions, chance, and the relative numbers of each species at the start of the experiment.
What has to happen for exclusion of a species to occur under exploitation competition
One organism must require less of the limiting resource to survive and reduce the quantity of the resource below some critical level
For two species to coexist under exploitation competition they must...
Partition the resource
When species coexist, what happens to their potential for growth?
Interference competition usually results in what?
Exclusion of one competitor
Model suggesting that two species cannot compete for the same limiting resource for long. Even a minute reproductive advantage leads to the replacement of one species by the other.
Competitive Exclusion Principal
A famous experiment by the Russian ecologist, G.F. Gausse demonstrated that Paramecium aurellia outcompetes and displaces Paramecium caudatum in mixed laboratory cultures, apparently confirming the principle.
(Interestingly, this is not always the case. Later studies suggest that the particular strains involved affect the outcome of this interaction
Competitive Exclusion Principle
Which species generally decreases in mixed populations of P. aurelia and P. Caudatum
Species that share the same habitat and have similar needs frequently use resources in somewhat different ways - so that they do not come into direct competition for at least part of the limiting resource. This is called
obviates competitive exclusion, allowing the coexistence of several species using the same limiting resource.
could be an evolutionary response to interspecific competition, or it could simply be that competitive exclusion eliminates all situations where resource partitioning does not occur.
As many as five different species of anoles may exist in the same forest, but each stays restricted to a particular space: some occupy tree canopies, some occupy trunks, some forage close to the ground. This is an example of:
Sympatric populations of similar species frequently have differences in body structure relative to allopatric populations of the same species.
This is thought to be an evolutionary response to interspecific competition.
When the two species occur together, G. fuliginosa has a much narrower beak that G fortis. Sympatric populations of G fuliginosa eats smaller seeds than G fortis: they partition the resource. Thought to be evolved in response to interspecific competition. This is an example of:
Character Displacement (on separate islands, both have intermediate beaks)
the set of resources and habitats an organism could theoretically use under ideal conditions.
the set of resources and habitats an organism actually used: it is generally much more restricted due to interspecific competition (or predation.)
Gausse's rule states that....
Two organisms cannot occupy exactly the same niche.
To explain Gauss's law it is thought that the more complex environments found in nature may enable more
when one species suffers and the other interacting species experiences no effect.
Redwood trees falling into the ocean become floating battering-rams during storms, killing large numbers of mussels and other inter-tidal organisms is an example of
involves the production and release of chemical substances by one species that inhibit the growth of another
chemicals produced by plants that seen to have no direct use in umetabolism, such as allelopathies
Allelopathy can be seen as amensalism and one sided...
Black Walnut (Juglans nigra) trees excrete an antibiotic called juglone. Juglone is known to inhibit the growth of trees, shrubs, grasses, and herbs found growing near black walnut trees.
Certain species of shrubs, notably Salvia leucophylla (mint) and Artemisia californica (sagebrush) are known to produce allelopathic substances that accumulate in the soil during the dry season. These substances inhibit the germination and growth of grasses and herbs in an area up to 1 to 2 meters from the secreting plants.
an interspecific interaction where one species benefits and the other is unaffected. Ubiquitous in nature.
Birds nesting in trees is an example of...
These kind of organisms frequently live in nests or bodies of other species
Ant colonies harbor rove beetles as commensals. These beetles mimic the ants behavior, and pass as ants. They eat detritus and dead ants.
Anemonefish live within the tentacles of anemones. They have specialized mucus membranes that render them immune to the anemone’s stings. They gain protection by living in this way.
An interspecific interaction between two species that benefits both members.
Populations of each species grow, survive and/or reproduce at a higher rate in the presence of the other species.
Widespread in nature, and occur among many different types of organisms.
Mychorrhizae increase the capability of plant roots to absorb nutrients. In return, the host provides support and a supply of carbohydrates.
Many corals have endosymbiotic organisms called zooxanthellae (usually a dinoflagellate). These provide the corals with carbohydrates via photosynthesis. In return, they receive a relatively protected habitat from the body of the coral.
a type of mutualism in which individuals interact physically, or even live within the body of the other mutualist. Frequently, the relationship is essential for the survival of at least one member.
Lichens are a fungal-algal symbiosis (that frequently includes a third member, a cyanobacterium.) The mass of fungal hyphae provides a protected habitat for the algae, and takes up water and nutrients for the algae. In return, the algae (and cynaobacteria) provide carbohydrates as a source of energy for the fungus.
Mutualisms that are not essential for the survival of either species. Individuals of each species engage in mutualism when the other species is present.
essential for the survival of one or both species.
These 4 organisms obtain food at the expense of their hosts or prey.
predators, parasites, parasitoids, and herbivores
tend to be larger than their prey, and consume many prey during their lifetimes
These are smaller than their host.
Parasites and pathogens
These may have one or many hosts during their lifetime, and consume the host from either the outside or inside
These are parasitic microbes-many generations may live within the same host
A parasite that consumes its host from the inside
A parasite that consumes its from the outside
These hunt their prey like predators, but lay their eggs within the body of a host, where they develop
Animals that eat plants. This interaction may resemble predation, or parasitism.
The relationships between predator and prey, and parasites and hosts, have coevolved over long periods of time.
Predator-Prey and Parasite-Host Coevolution
First a parasite (or predator) evolves a trait that allows it to attack its host (or prey).
Next, natural selection favors host individuals that are able to defend themselves against the new trait.
As the frequency of resistant host individuals increases, there is natural selection for parasites with novel traits to subvert the host defenses.
This process continues as long as both species survive.
Evolutionary Arms Race
The common milkweed, Asclepias syriaca has leaves that contain cardiac glycosides: they are very poisonous to most herbivores. This renders them virtually immune to herbivory by most species
Parasite host Coevolution
Monarch butterfly larvae have evolved the ability to tolerate these toxins, and sequester them within their bodies. They are important specialist hervivores of milkweeds.
Parasite host coevolution
These sequestered compounds serve the additional purpose of making monarch larvae virtually inedible to vertebrate predators.
Predation is what kind of mortality factor to the host population?
Prey rmay epresent what to the predators?
The density of the prey population, in turn, affects the birth and death rates of the predator population.
i.e, when prey become particularly common, predators increase in numbers until prey die back due to increased predation, this, in turn, inhibits the growth of prey.
Predation-Prey Population Dynamics
Occurs between predators and prey and is necessary for the stability of both populations.
Feedback mechanisms may control the densities of both species
A method of control of the prickly pear cactus was initiated with the introduction of Cactoblastis cactorum, a cactus eating moth from Argentina, in 1925. By 1930, densities of the prickly pear cactus were significantly reduced.
Regulation by a host population (predator prey dynamics)
In other cases, there are alternate prey to support the predator and the prey is permanently excluded
Ya, like the freshwater fish , which exclude other fish to other prey like insect larvae
Most predators do not respond instantaneously to the availability of prey and adjust their reproduction accordingly.
If predator populations grow faster than prey populations, they may overshoot the number of prey that are able to support them