Community Ecology Flashcards
An assemblage of plant and animal populations that live in a particular area or habitat.
Community
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.
Interaction
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
True/False
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
Patterns
Examples include processes-herbivory, competition, predation risk, nutrient availability, patterns of disturbance, energy flow, history, and evolution
Processes
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.
Spatial Structure
An example of this is trees in a rainforest stratifying into several different layers, each with a habitat of a distinct collection of species
Spatial Structure
The time of the appearance and activity of species
Ex: arctic tundra, seasonal ponds, desert plants and animals that emerge after seasonal rains
Temporal Structure
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
Species Richness
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.
Diversity
Some communities, such as tropical rainforests, are much more diverse than others, such as the great basin desert.
Yup
Species Diversity is often expressed using Simpson’s diversity index:
D=1-S (pi)2
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.
Ecological Succession
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
Ecological Succession
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.
Ecological Succession
creates opportunities for new species to invade an area and establish themselves.
Disturbance
These species modify the environment, and create opportunities for other species to invade, The new species eventually displace the original ones
Invasion
Eventually, the new species, in turn modify the environment enough to allow a new series of invaders, which ultimately replace them, etc
Succession
events such as floods, fire, droughts, overgrazing, and human activity that damage communities, remove organisms from them, and alter resource availability.
Disturbance
The best invaders have good dispersal powers and many offspring, but they are often not the best competitors in the long run
Word!
Disturbance of a community is usually followed by recovery, called?
This sequence is driven by the interactions among dispersal, ecological tolerances, and competitive ability.
Ecological Succession
The sequence of species on newly exposed landforms that have not previously been influenced by a community, e.g., areas exposed by glacial retreat.
Primary Succession
occurs in cases which vegetation of an area has been partially or completely removed, but where soil, seeds, and spores remain
Secondary Succession
Early in succession, species are generally excellent dispersers and good at tolerating harsh environments, but not the best interspecific competitors
Yeah
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
Yup
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.
Word
is a more or less permanent and final stage of a particular succession, often characteristic of a restricted area.
Climax Community
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?
Gleason
True False: Disturbance and nonequilibrium are abnormal for most communties
False
Communities usually are in a state of recovery from disturbance
True
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
Ch’yeah!
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
Trophic Interaction
For every community, a diagram of trophic interactions is called
-Energy flows from the bottom to the top
Food web
One pattern through a food web
Food chain
An organism’s habitat, the resources it uses, and its way of making a living, within the context of a community
Niche
Very important in community ecology, yet it remains controversial because they are difficult or impossible to observe directly.
Niche
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
Niche
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
Keystone Species
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.
Pisaster Starfish
This keystone species disperses in salt water. They take root and form a dense forest in saltwater shallows, allowing other species to thrive
Mangrove Trees
