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Community ecology basics

I. Basic ecological concepts

A. Habitat - is the physical setting, or place, in which an organism lives
e.g. a forest or desert of coral reef

B. Niche - is the ranges of conditions that the organism can survive, and the methods of living that an organism can pursue
e.g. for a coral reef - the water temperatures, salinities, wave action, nutrients and light level required to survive, the food it consumes, competitors it forages with and the predators that consume it, all make up its niche

1. Can plot 2 niche variable opposite one another to see how two species in a community differ or overlap (compete) in niche

2. Niche overlap = competition

3. Niche compression = minimization of competition

C. Environmental tolerance - the range of environmental conditions that an organism can withstand. - range decreases (becomes more specific) as you move from survival to growth to reproduction, from barely tolerable to comfortable to optimal.

D. Distribution - geographic range of a species, due in large part to environmental tolerances, but also to competition with other organisms.

E. Population - members of a given species living in the same area at the same time and relying on the same resources.

II. Community ecology terms

A. Community - an association of interacting species inhabiting some defined area.

1. A collection of species may interact directly (predation) or indirectly (earthworm recycling nutrients for tree).

2. Community ecology considers how various biotic (living) and abiotic (non-living) factors of the environment effect the structure of a community.
   biotic = species that make up the community
   abiotic = temp., rainfall, slope, wave action, soil, etc.

B. Autotrophic community- require only the energy of the sun to exist (photosynthetic communities)
often a community is described by its autotrophic component - you say that you are sampling a Northern Hardwood community or an Oak Hickory community - but this often refers to the heterotrophic organisms that live within this community as well.

C. Heterotrophic community - depend on the autotrophic community for their energy

1. Primary consumers

2. Secondary consumers, etc

3. Food chain - one possible pathway for the passage of energy from prey to consumer

4. Food web - multiple overlapping food chains

D. Dominance - one or more species that dominate a community

1. may be the most numerous

2. may have the highest biomass

3. may preempt the most space (on rocks or as a canopy)
   - small trees may be most numerous, but emergent trees limit the amount of light reaching them.

4. may make the largest contribution to energy flow or nutrient cycling

5. may dominate based on its activity - keystone predators - will discuss this later

III. Species abundance & diversity - the number of species and the relative abundance (#) of each species describes a community.

A. Species richness - number of species in a community

B. Species evenness - relative abundance (#) of individuals among the species
100 individuals - 10 in each of 10 species, or 90 in one species, and 1 in each of 10 others.

C. Species diversity = a measure including both number of species (species richness) and their relative abundance (species evenness).

1. If species # is the same in two communities, then the one with greater evenness will have greater diversity.

2. Species diversity is higher in structurally complex environments
   we will examine this, is species diversity higher in a hardwood forest than a more homogeneous highland forest, etc?

3. Intermediate disturbance hypothesis - species diversity is highest in areas of intermediate disturbance

4. Calculating species diversity

D. Lognormal distribution - generally you will find the following generalization to be true about nearly every community - few species are rare, many are common and few are abundant.

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