Why are organisms absent some places and abundant in others?
--> Abiotic Forces: plants have certain limits regarding environmental tolerances.
Temperature, moisture, sunlight, pH, substratum, salinity, atmosphere, etc.
-->Biotic Forces: Organisms compete for space and resources, and some eat others.
Competition, predation, symbiosis, habitat modification.
-->Opportunity (history): organisms are absent where there is no geographical access.
The primary issues surrounding the nature of communities can be divide roughly into those of pattern and process.
The issues of pattern focuses on how species and communities are distributed over the landscape. – Are boundaries abrupt or gradual?
– How predictable are the patterns?
The issues of process focus on what processes (e.g., competition, herbivory, history) actually function in natural communities and which of these are most important in determining the observed patterns.
– Do some processes predominate?
– Do processes vary among communities?
– Do different species respond to processes…