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Biology 2108 Lecture
Ecology: Communites

Community
- all populations in a specific area

Examples of questions in community ecology include: to what degree do populations 'behave' differently together then when alone; how do interactions maintain diversity; how important are these interactions in determining species composition of a community; and how stable are species assemblages over time?


Let's examine the first question: do populations 'behave' differently together then when alone?

 


Types of interactions
between two populations (species)



Species that share similar niches (the niche is the range of abiotic and biotic under which a species can live) are likely to be competing for a similar limiting resource.  What can happen if two species living in the same community occupy very similar niches?



Are parasites predators?  Are herbivores predators?  
The evolutionary importance of predation is clearly demonstrated in the sophisticated predator and prey adaptions.  Co-evolution is very intense in these interactions because improved adaptation of one species will directly affect other, resulting in sophisticated adaptations.

For example, c
amouflage: 

Is being the same color as the dominant background color necessarily the most adaptive coloration strategy?





The importance of community interactions: 

Persistence of interactions (how interactions maintain diversity)

If population are not always stable and many interactions between populations are harmful, how do species persist over time (how is diversity maintained)?
 

Examples of competition and predation coexistence:

The importance of these interactions in maintaining diversity is demonstrated by success of exotic (invasive) species at the expense of native species.

What happens when humans introduce species into  communities in which they have not evolved?  Why do some species do better in environments in  which they did not evolve than in they do in the environment in which they did evolve?

  For example, Rabbits in Australia


Non-native species placed in a new environment no longer have to interact with the species that have adapted to take advantage of them.


'The intermediate disturbance hypothesies' - diversity of a community tends to be highest where disturbances are of intermediate intensity:

The number of species may remain fairly constant over time.

For example, the number of species on an island is directly related to island size (as a result of an equilibrium between species extinction and immigration).
How might this be useful in predicting loss of biodiversity as a result of habitat destruction and fragmentation?

Changes in species composition of community over time are well documented:
Ecological Succession - a fairly predictable change in species compostion over time.

Typically, the series of community changes begins with a disturbance
 

Examples of succession:

What drives ecological succession?  How is the presence of later-succession species dependent upon early ones modifying the environment so that it is favorable to the later? 

Bottom line:  Species interact in numerous ways within communities and many of these interactions important in maintaining diversity.  But non-equilibrium processes can also be important in positively influencing diversity, demonstrating that natural systems are dynamic.
 


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