1

Evolution, Biological Communities,and Species Interactions

2

Outline

• Evolution and Speciation• Species Interactions• Community Properties• Communities in Transition• Introduced Species and Community Change

3

Definitions

• evolution – • genetic changes within a population over time• natural selection – • differential reproductive success• mutations –• random changes

in DNA• adaptation – • genetic trait that

confers a selective advan-

tage in a given environment

4

Critical Limits

• Von Liebig proposed the single factor in shortest supply relative to demand is the critical determinant in species distribution. Shelford later expanded by stating each

environmental factor has both minimum and maximum levels, tolerance limits, beyond which a particular species cannot survive.

5

Tolerance Limits

Tolerance Limits – for every environmental factor, an organism has maximum and minimum levels beyond which it can’t survive.

Answers: What are the unique factors that limit growth of a population?

6

Critical Limits

• For many species, the interaction of several factors, rather than a single limiting factor, determines biogeographical distribution. For some organisms, there may be a

specific critical factor that mostly determines abundance and distribution.

• Species requirements and tolerances can also be used as useful indicators. Environmental indicators

7

Variation

• Four conditions are necessary for evolution to occur 1. variation in traits in a population 2. traits must affect reproductive success 3. traits must be inheritable 4. some selective pressure must favor

these traits differentially

8

Selective Pressure

• Environmental factors that favor survival and increase reproductive success of some individuals over others can lead to evolution.

• Natural selection modifies populations so that they are better suited to their environment.

9

10

• resource partitioning - groups of individuals become specialized to utilize sub-sets of the same resource

• radiative evolution - divergence from common ancestor into two or more species

11

Reproductive Isolation

• Isolation prevents gene flow between members of a species

12

Two types of speciation:

Allopatric:

due to geographic separation

13

Reproductive Isolating Mechanisms• mechanical - structural differences

• temporal - different timing for breeding

• behavioral - courtship displays

• ecological - different ecological roles

Sympatric - does not require geographic separation

14

Evolution at Work

• Artificial selection

• Pesticide and antibiotic resistance

15

Ecological Niche• Habitat –

Place or set of environmental conditions where a particular organism lives.

• Ecological Niche – Description of the role a species plays in a biological

community, or the total set of environmental factors that determines species distribution.

Generalists –- Broad niche

Specialists – - Narrow niche

16

Resource Partitioning

• Law of Competitive Exclusion – • No two species will occupy the same niche

and compete for exactly the same resources for an extended period of time. One will either migrate, become extinct, or

partition the resource and utilize a sub-set of the same resource.

- Given resource can only be partitioned a finite number of times.

17

Resource Partitioning

18

SPECIES INTERACTIONS

Predator • is an organism that feeds directly upon

another living organism, whether or not it kills the prey in doing so. Prey most successfully on slowest,

weakest, least fit members of target population.

- Reduce competition, population overgrowth, and stimulate natural selection.

Co-evolution

19

Co-Evolution

20

Keystone Species

• A species or group of species whose impact on its community or ecosystem is much larger and more influential than would be expected from mere abundance.

Often, many species are intricately interconnected so that it is difficult to tell which is the essential component.

21

22

Competition• Interspecific –

Competition between members of different species.

• Intraspecific – Competition among members of the same

species. Often intense due to same space and

nutritional requirements.- Territoriality - Organisms defend specific

area containing resources, primarily against members of own species.

Resource Allocation and Spacing

23

Symbiosis• Symbiosis –

Intimate living together of members of two or more species.

Commensalism – - One member benefits while other is neither benefited

nor harmed.- Cattle and Cattle Egrets

Mutualism – - Both members benefit.- Lichens (Fungus and Cyanobacterium)

Parasitism – - One member benefits at the expense of other.

Humans and Tapeworms

24

25

Defensive Mechanisms Batesian Mimicry – Harmless species evolve characteristics that

mimic unpalatable or poisonous species.

26

Mullerian Mimicry

Two unpalatable species evolve to look alike.

• Two or more harmful species, that are not closely related and share one or more common predators, have come to mimic each other's warning signals.

• Ex. Heliconius butterflies

Perhaps one of the most well-known examples of mimicry, the viceroy butterfly (top) appears very similar to the noxious tasting monarch butterfly (bottom). Although it was for a long time purported to be an example of Batesian mimicry, it has recently been discovered that the viceroy is actually just as unpalatable as the monarch, making this a case of Müllerian mimicry.[8]

27

COMMUNITY PROPERTIES

• Primary Productivity – • Rate of biomass production. Used as an

indication of the rate of solar energy conversion to chemical energy. Net Primary Productivity - Energy left after

respiration.

28

29

Abundance and Diversity

• Abundance -Total number of organisms in a community.

• Diversity - Number of different species, ecological niches, or genetic variation. Abundance of a particular species often

inversely related to community diversity. As general rule, diversity decreases and

abundance within species increases when moving from the equator to the poles.

30

Community Structure

31

Complexity and Connectedness

• Complexity Number of species at each trophic level,

and the number of trophic levels, in a community.

32

Edges and Boundaries

• Edge Effects Important aspect of community structure is the

boundary between one habitat and others.• Ecotones

Boundaries between adjacent communities.- Sharp boundaries - Closed communities- Indistinct boundaries - Open communities

33

Edges and Shapes

34

Ecogical Succession: Primary Succession

35

Primary Succession

36

37

Secondary Succession

38

Secondary Succession

39

Disclimax communities/Equilibrium communities

40

41

COMMUNITIES IN TRANSITION

• Ecological Succession Primary Succession A community begins to develop on a site

previously unoccupied by living organisms.- Pioneer Species

Secondary Succession An existing community is disrupted and a

new one subsequently develops at the site.

42

Ecological Succession

• Process of environmental modification (facilitation) by organisms.

• Climax Community Community that develops and seemingly

resists further change. Equilibrium Communities (Disclimax

Communities) - Never reach stable climax because they are adapted to periodic disruption.

43

Introduced Species and Community Change

• If introduced species prey upon or compete more successfully than native populations, the nature of the community may be altered. Human history littered with examples of

introducing exotic species to solve problems caused by previous introductions.

- Mongoose and Rats in Caribbean

44

Summary

• Evolution and Speciation• Species Interactions• Community Properties• Communities in Transition• Introduced Species and Community Change

45