Thursday, January 8, 2009

Ecology Unit

Here are the notes for today:


Symbiosis is a term applied to two species that live together in close contact during a portion (or all) of their lives. A description of three forms of symbiosis follows:

1. Mutualism is a relationship in which both species benefit. (++)

2.In commensalisms, one species benefits, while the second species is neither helped nor harmed (+0)

3.In parasitism, the parasite from the living arrangement, while the host is harmed (+-)

Camouflage (or cryptic coloration) is any color or pattern, shape, or behavior that enables an animal to blend in with its surroundings. Both prey and predator benefit from camouflage.
Can you spot the insect?

Aposematic coloration (or warning coloration) is a conspicuous pattern or coloration of animals that warms predators that they sting, bite, taste bad, or are otherwise to be avoided.

Mimicry occurs when two or more species resemble one another in appearance. There are two kinds of mimicry:

Mullerian mimicry occurs when several animals, all with some special defense mechanism, share the same coloration. Mullerian mimicry is an effective strategy because a single pattern, shared among several animals, is more easily learned by predator than would be a different pattern for every animal.

Batesian mimicry occurs when an animal without any special defense mechanism mimics the coloration of an animal that does posses a defense.

Ecological succession

Ecological succession is the change in the composition of species over time. The traditional view of succession describes how one community with certain species is gradually and predictably replaced by another community consisting of different species.

As succession progresses, species diversity (the number of species in a community) and total biomass (the total mass of living organisms) increase. Eventually, a final successional stage of constant species composition, called the climax community, it attained. The climax community persists relatively unchanged until destroyed by some catastrophic event, such as fire.

Succession occurs in some regions when climate changes over thousands of year. Over shorter periods of time, succession occurs because species that make up communities alter the habitat by their presence. In both cases, the physical and biological conditions which made the habitat initially attractive to the resident species may no longer exist, and the habitat may be more favorable to new species. Some of the changes induced by resident species are listed below:

1.Substrate texture may change from solid rock, to sand, to fertile soil, as rock erodes and the decomposition of plants and animals occurs.

2.Soil pH may decrease due to the decomposition of certain organic matter, such as acidic leaves.,

3.Soil water potential, or the ability of the soil to retain water, changes as the soil texture changes

4.Light availability may change from full sunlight to partly shady, to near darkness as trees become established

5.Crowding, which increases with population growth, may be unsuitable to certain species

Succession is often described by the series of plant communities that inhibit a region over time. Animals, too, take up residence in these communities but usually in response to their attraction to the kinds of resident plants, not because of any way in which previous animals have changed the habitat.

The plants and animals that are first to colonize a newly exposed habitat are called pioneer species. They are typically opportunistic, r-selected species that have good dispersal capabilities, are fast growing, and produce many progeny rapidly.

As soil, water, light and other condition change, r-selected species are gradually replaced by more stable K-selected species. These include perennial grasses, herbs, shrubs, and trees. Because K-selected species live longer, their environmental effects slow down the rate of succession. Once the climax community is established, it may remain essentially unchanged for hundreds of years.

r-selected species
• Good colonizers
• Reach sexual maturity rapidly
• Short-lived
• High fecundity
• Low investment in care for the young
• Generalist
• Poor competitors

K-selected species
• Poor colonizers
• Slow maturity
• Long-lived
• Low fecundity
• High investment in care for the young
• Specialist
• Good competitors

Here's a graph showing what the curves for k and r-selected species look like:

Some key terms for this chapter:

Character displacement-The tendency for characteristics to be more divergent in sympatric populations of two species than in allopatric populations of the same two species.

Competitive exclusion-The concept that when populations of two similar species compete for the same limited resources, one population will use the resources more efficiently and have a reproductive advantage that will eventually lead to the elimination of the other population.

Disturbance-A natural or human-caused event that changes a biological community and usually removes organisms from it. Disturbances, such as fires and storms, play a pivotal role in structuring many communities.

Ecological niche-The sum of a species’ use of the biotic and abiotic resources in its environment.

Ecological succession-Transition in the species composition of a community following a disturbance; the establishment of a community in an area virtually barren of life.

Interspecific competition-Competition for resources between individuals of two or more species when resources are in short supply.

Interspecific interaction-A relationship between individuals of two or more species in a community.

Keystone species-A species that is not necessarily abundant in a community yet exerts strong control on community structure by the nature of its ecological role or niche.

Primary succession-A type of ecological succession that occurs in an area where there were originally no organisms present and where soil has not yet formed.

Resource partitioning-The division of environmental resources by coexisting species such that the niche of each species differs by one or more significant factors from the niches of all coexisting species.

Secondary succession-A type of succession that occurs where an existing community has been cleared by some disturbance that leaves the soil or substrate intact.

Symbiosis-An ecological relationship between organisms of two different species that live together in direct and intimate contact.

Trophic structure-The different feeding relationships in an ecosystem, which determine the route of energy flow and the pattern of chemical cycling.

Multiple Choice Questions

1. A lizard living on the leaves and branches of a tree while an owl nests in the hollow of the trunk is an example of:

  1. Interspecific Competition
  2. Character displacement
  3. Resource partitioning
  4. Predation
2. An example of mutalism is:

A. A bird eating bugs of the hide of a cow
B. A tick on the skin of a human
C. An ant on the acacia tree
D. A barnacle on a humpback whale

3. An ecological disturbance is:

A. Created by humans
B. A fire
C. A storm
D. A, B, and C

Answers: 1:3, 2:C, and 3:D

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