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24 Cards in this Set
- Front
- Back
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Ecological community |
Group of species that coexist in a space and time and interact with one another directly or indirectly Firstly, community represents the biotic or a living component of the ecosystem Secondly, communities are made up of organisms with interlocking food chains Thirdly, community may be of any size |
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Dominant species |
Which by their large number (or biomass) dominate the habitat and control the growth of other species of the community |
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Keystone species |
Activity of the species determines the community structure in spite of their low abundance or biomass |
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Species richness |
Number of species in a community |
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Species evenness |
Relative abundance of the species |
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Evenness vs. dominance |
Communities in which the species are all more or less equal in abundance exhibit evenness whereas communities with one or a few abundant species show dominance |
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Diversity index |
Mathematical measure of species diversity in a community Measure of the number of species in an area and the relative abundance of individuals among those species |
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Diversity index categories |
Dominance indices and information statistic indices |
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Simpson’s diversity index |
Simple mathematical measure that characterises species diversity in a community |
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Simpson’s index (D) |
Measure of the species diversity of an ecosystem based on the concept of dominance It measures the probability that two individuals randomly selected from a sample will belong to the same species It is actually a measurement of dominance |
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Shannon diversity index (or Shannon Wiener index) |
Another index that is commonly used to characterise species diversity in a community It is a measure of the species diversity in a community asked on information theory I.e. greater diversity corresponds to greater uncertainty in picking at random am individual of a particular species |
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Pielou’s evenness index (J’) |
A diversity index which quantifies how equal the community is numerically I.e. evenness of community It is the ratio of observed diversity (H’) to the maximum possible diversity of a community with the same species richness (H’ max) |
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Disturbance |
An ecological sense, is an event, such as a storm, fire, flood, drought, overgrazing, or human activity that changes a community by removing organisms from it or altering resource availability It influences species coexistence and the maintenance of biodiversity |
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Intensity |
Measured by the proportion of total biomass or population of a species that the disturbance kills or eliminates |
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Frequency |
The mean number of disturbances that occur within a particular time interval |
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Intermediate disturbance hypothesis |
Species diversity is higher at intermediate intensities or frequencies of disturbance due to a mix of good coloniser and good competitor species |
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Two components of stability in ecology |
Resistance and resilience |
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Resistance |
How tolerant a community is towards a disturbance before it changes It describes the ability to resist disturbances |
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Resilience |
Refers to how quickly a community can return to equilibrium after a disturbance It describes the ability of a community to return to its original state quickly following displacement |
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Diversity stability hypothesis |
Stated that the more diverse a community is the more stable and productive the community is |
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Community complexity |
Function of the magnitude of interactions between community components Complexity increases as the number of interacting species in the community increases These interactions can be horizontal or vertical |
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Ecotone |
The transition zone of vegetation separating two different types of communities |
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Edge effect |
The phenomenon of increased species diversity at the boundary Essentially due to wider range of suitable environmental conditions It is influenced by the area of transition zone (length and width) and by the degree of contrast between adjoining communities |
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Edge species |
Species that occur primarily and most abundantly at the edge for the purposes of reproduction and survival |
