Dr. Paul Colinvaux

Every species has its niche

(1978)

ecological, analytical, reductionist, abstract

Dr. G. Tyler Miller

Community Structure: Appearance & Species diversity, (2005)

biological, descriptive, integrative, visual

An ecologists view of life’s complexity

based on how a species copes.
“... its place in the grand scheme of things.”

I. Making a Living
II. Capacity of resources to sustain organisms
III. Reproductive strategies
IV. Conclusion

§§§

I Introduction explains "earning one’s keep"

A. complexity

1. hunting
2. breeding
3. seasons
4. competitive quest for food, fuel, fiber & forage

B. niche is defined

"its place in the grand scheme of things"

(p. 259)

uses wolf spiders

(Wilson's Storm, in ¶ 4, p. 153)

2 & 3: the complexity of a wolf spiders life [but wolf spidering is their niche ¶5]

4: defines NICHE as "a word borrowed from church architecture" (p. 260)

C contrast between niche (function) & habitat (place)

5: contrasts to "habitat "as a "physical living place, address or location

6: idea of "niche" helps us understand the "constancy of numbers."

20 ¶ paragraphs to explain "a lifestyle that enables it to survive...."

(p. 259)

9: "The reproductive effort makes no difference to the… population size"

II. Limitations inherent in Carrying Capacity

A. limits are defined

7 & 8: limitations on the number able to fill a niche

B. carrying capacity is defined

10: Carrying capacity is defined as a functional ability of land to sustain a certain size population over time without diminishing life’s ability through individuals to exploit available niches.

III. Competing reproductive strategies assure survival

A. natural selection argument

1. twin gambits

a. small - numerous egg strategy

thousands of eggs (see Zwinger, ¶ 22, p. 104) to show what is necessary to fill a niche

¶ 10, "The actual number of those who will be able to live in that next generation has been fixed by the environment; we may say that the population will be a function of the carrying capacity of the land for animals of this kind in that time & place."

¶ 13, "A selfish race of neighbor against neighbor leads to those thousands of tiny eggs and the early deaths of the babies are the cost of this selfishness."

b. large young gambit

2. numbers of eggs and food supply

B. economy of behavior
C. optimization of time, expenditures and resources

VI. Conclusion

Niche is a means to understand

1. the physical and chemical constraints
   
2. imposed on biological organisms
   
   1. by the environment’s capacity
      
   2. to assimilate growing numbers on limited resources.

Paul Colinvaux “Every species has its niche” (p. 259-264)

Ecologists describe the structure of a community in terms of its physical appearance, species diversity, species abundance, and niche structure.

Differences at boundaries between two ecosystems result in edge effects.

I. What do species do ecologically?

II. Species types

III. Competiton and predation

IV. Successional plant associations

7-1 Species diversity, appearnace of dominance.

Species diversity on continents declines with distance from the equator (latitude). In marine communities, species diversity varies with depth and pollution levels. In terrestrial communities, species diversity increases with increasing solar radiation, increasing precipitation, decreased elevation, and pronounced seasonal variations.

MacArthur and Wilson's species equilibrium model predicts that species diversity will increase with island size and with proximity to a mainland. Field experiments have supported the model.

7-2 General Types of Species

Many native species have suffered as a result of the introduction of nonnative species.

Birds are excellent indicator species and can serve as an early warning of damage to a community.

The decline of a keystone species can cause a ripple effect through an ecosystem.

7-3 Species Interactions: Competition and Predation

Intraspecific competition can be intense because members of the same species require the same resources.

The more the niches of two species overlap, the greater the degree of interspecific competition. Over time, resource partitioning may enable similar species to coexist.

Predation benefits a predator at the expense of its prey. Carnivores feed on mobile prey;  herbivores feed on plants. Predators have evolved a variety of ways to increase their chances of finding food, and prey have evolved various ways to defend themselves against or avoid predators.

7-4 Symbiotic Species: Parasitism, Mutualism, and Commensalism

There are three types of symbioses among organisms: parasitism, mutualism, and commensalism.

7-5 Ecological Succession: Communities in Transition

The two types of ecological succession are primary succession and secondary succession.

With primary succession, pioneer species colonize an area. Over time, they may be replaced by early successional plant species, which may be replaced by midsuccessional plant species.

These species can give way to late successional plant species. However, research indicates that we cannot predict the course of succession or view it as progress toward an ideally adapted climax community.

Disturbances or changes in environmental conditions disrupt an ecosystem or community and affect its species diversity and stage of succession.

Such as:


• Storms
• hurricames
• fires
• volcanoes
• floods
• earthquakes

According to the intermediate-disturbance hypothesis, communities that experience fairly frequent but moderate disturbances have the greatest species diversity.

Miller, Chapter 7, pp. 140-157

His article is important because:
Creates a structure to understand Wilson, Dillard, Myers, & Leopold.
Introduces game theory in the form of strategies for reproduction.

Is a prerequisite for understanding Hardin’s “The Tragedy of the Commons.”
Calls our attention to constraints on reproduction, dispersal and survival.

The chapter's importance lies in the fact that it suggests signals we need to read if we are to understand the fitness of the ecological system to sustain, both human and non-human needs.

The chapter establishes two kinds of capacity:

Carrying capacity is the absolute number of creatures an ecosystem's vegetation may sustain without diminishing future needs.

Assimilative capacity is the quanitity of pollutions, harm, or decay an ecosystem may sustain before its capacity to nourish additional organisms is depleted.

Paradox of competitive exclusion:
“Every family tries to outbreed every other, though the total numbers remain the same”

Paradox of ecosystem stability as it emerges out of competitive behavior, partitioning and symbiotic arrangements to accustom creatures to adapt to losses of or changes in keystone species.

Adaptive responses are needed to both changes in habitat and changes in species mixture.