Gen Eco Lecture 12-13

Definitions

100

Community

An interacting assemblage of populations of different organisms living in a defined area or habitat

200

Guild

A group of species that exploit similar resources in similar ways

300

Physical Structure

Abiotic factors

Spatial configuration of organisms

400

Biological Structure

Mix of species

Abundance and diversity

500

Spatial Configuration of Organism

A well developed forest ecosystem has several layers of vegetation

2

100

Patchiness can exist at all:

Levels

Sizes

Shapes

Dispersion

200

Maximum Diversity (H_max)

What the H' value would be if the community was at maximum diversity based on its values of R and N

H_max = ln(R)

300

Latitude Diversity Gradient

The observation that species diversity tends to increase at low latitudes (tropics) and decrease at high latitudes (poles)

400

Evolutionary Speed Hypothesis

(Diversity Gradients)

Tropical systems evolve faster

Biota in the warm, humid tropics are likely to evolve faster than higher latitude due to constant favorable environment and freedom from climatic disasters

500

Increased Interspecific Interactions

(Diversity Gradients)

Natural selection is primarily driven by abiotic factors in the temperate and polar zones, and by biotic factors (species interactions) in the tropical zones

Quantifying Biological Structure

100

Abundance (N_i)

The total number of individuals in the population, or the number sampled

200

Richness (R)

The total number of taxa present

Most common index is 'species richness'

300

Relative Abundance (Pi)

The proportion of individuals in a community represented by a particular species (N_i). 

Illustrates how evenly the community is spread out across the richness

Pi = N_i/N

400

Species Diversity

A quantitative index that considers species richness and equitability. The most common index is the Shannon - Wiener Index.

H' = -∑ Piln Pi

500

Evenness (E)

A measure of how equitable the total abundance (N) is spread across the richness (R)

4

100

Succession

Change in community structure through time

200

Climax Community

The final stage of succession, a community that remains relatively unchanged until reset by a disturbance

300

Seral Stages

The actual types of communities that develop within each successional phase. Defined by the dominant plant communities that develop 

400

Primary Succession

Occurs when organisms colonize barren, lifeless, habitat for the first time

After glaciation, volcanoes, or exposure of newly exposed landscapes

500

Secondary Succession

Recovery of a disturbed site where a biological community has already existed

After fires, storms, land clearing

5

100

Direct Observation

Study it while it is occurring, clearest way to document change over time. 

200

Indirect Observation

Examine communities that exist in the same region but differ in their age

300

Chronosequence

A set of ecological sites that share similar attributes but represent different ages. Ideally, the only environmental variable that differs between sites is age. 

400

Mechanisms of Succession

Facilitation

Inhibition

Tolerance

500

Early vs Late Succession Traits

Early - adaptations that promote dispersal and rapid growth

Late - adaptations that enhance competitive ability