4/10 pt.1: In-depth Notes on Competition and Niche Space (REC.1)(DOC)

Competition in Ecology

• Definition: Competition is a common interaction in natural ecosystems that serves as a critical driver of natural selection.

  • Can occur directly (with organisms in the same physical space) or indirectly (effects of one individual on another without direct contact).

• Role in Evolution:

  • Better competitors are more likely to reproduce and pass on their traits to the next generation, leading to populations that are increasingly composed of effective competitors.

Community Ecology

• Context: Competition is a part of the larger field of community ecology, which deals with how species interact within a community.

• Costs and Benefits:

  • Competing individuals experience costs (energy loss, reduced fitness) and potential benefits (access to resources).

  • Costs manifest as decreased fitness if competition occurs, but benefits might lead to healthier offspring.

Types of Competition

• Minus-minus Interaction:

  • Competition is considered a minus-minus interaction, indicating both individuals suffer costs from competing over limited resources.

  • Examples of resources competed for include food, space, mates, and light for plants.

Intraspecific Competition

• Definition: Competition occurring within the same species.

  • Individuals compete for identical resources, leading to significant interaction and impacts on population dynamics.

  • Density-Dependent Growth: The population dynamics in the context of intraspecific competition suggest that as population density increases, competition intensifies, leading to slowed growth rates.

Interspecific Competition

• Definition: Competition between individuals of different species.

  • Although some believe interspecific competition is more intense, intraspecific competition tends to have a larger impact due to resource overlap.

Niche Space

• Definition: The sum of environmental factors that allow a species to exist, which includes resource needs, abiotic factors, and interactions with other species.

• Niche Space Misconceptions: Previous definitions equating niche to the role of a species in an ecosystem are too simplistic; niche space encompasses all survival requirements.

• N-Dimensional Hypervolume: A conceptual extension that represents the complexity of each species' niche requirements.

Fundamental vs. Realized Niche

• Fundamental Niche: Represents all the possible conditions and resources a species can utilize in the absence of competition.

• Realized Niche: The actual conditions and resources utilized when competition is present; often narrower than the fundamental niche due to competition.

Competitive Exclusion Principle

• Definition: Two species with identical niche requirements cannot coexist indefinitely; one will outcompete the other.

• Example of Resource Partitioning:

  • Segregation of habitats and resources allows similar species to coexist without direct competition for identical resources.

Resource Partitioning vs. Resource Segregation

• Resource Partitioning: How resources are divvied up among competitors to minimize competition (e.g., birds foraging at different heights).

• Resource Segregation: Identification of distinct requirements that enable species to differentiate their niches.

Scramble vs. Interference Competition

• Scramble Competition: Involves direct competition for a resource; individuals target the resource itself.

• Interference Competition: Involves actions against other competitors to prevent them from accessing a resource.

Case Studies:

1. Dung Beetles:

   • Scramble Competition: Males rush to gain access to dung before others.

   • Interference Competition: Males may also fight over dung that's been collected.

2. Barnacles:

   • Compete for available substrate; while mostly scramble competition, the density of barnacles can block new larvae's access, suggesting an interference component.

3. Hyenas and Vultures:

   • Interference competition occurs as they each try to access a shared food source (the zebra).

4. Salvia Shrubs:

   • These plants produce allelochemicals to inhibit growth of nearby plants, exemplifying interference competition.

Conclusion

• Understanding the complex interactions between species through competition, niche space, and resource management is critical in ecology, helping us predict species distributions and community dynamics.

Biol 114 In-class Assignment - Population Ecology

1) What is exponential growth? Describe the exponential growth model in terms of the variables r and N and

any limitations to population growth the model may predict.

Exponential growth is growth of a population without environmental limitations (there are limitations among

the individuals of the species) that is demonstrated by a relatively slow increase that quickly transitions to rapid

increase. The individuals of the population (who are considered all the same) each have a probability of dying

(d) and probability of contributing to population increase (b). Each individual can then be defined as having an

overall influence (r = the per capita growth rate) on population growth as a function of b-d. There are no

resource limitations for a population growing in this manner. However, species-specific limitations, like rate of

reproduction, do exist.

2) What are the stages involved in a sigmoid-shaped growth curve? Draw a logistic growth curve. Describe

how r changes along the length of the curve and describe the factors responsible for the changes in r.

Early exponential growth (up to the inflection point), followed by a decrease (yet still positive) of growth, then

achieving some theoretical maximum population size. This is the theoretical model. However, real populations

do not achieve K and remain at that size, but will follow a changing K. In the logistic model, r is at its

maximum value during the early exponential growth phase, but then decreases from the inflection point onward.

In theory it reaches zero at K. Changes in r are due to decreasing resource availability and increased

competition among members of the population. In the exponential model r is at its maximum value always.

Low vs. High survivorship

1. Expects a large percentage of its offspring to die before maturity.

   1. Low survivorship

2. An example would be an elephant.

   1. High survivorship

3. Invests a small amount of resources in rearing offspring.

   1. Low survivorship

4. Has a Type III survivorship curve.

   1. Low survivorship

5. Has relatively few offspring.

   1. High survivorship

6. It is usually long-lived.

   1. High survivorship

7. An example would be an insect.

   1. Low survivorship

8. Has a Type I survivorship curve.

   1. High survivorship

9. Spends most energy on bodily maintenance.

   1. High survivorship

10. An example would be an annual plant.

    1. Low survivorship

11. An example would be a human.

    1. High survivorship

12. Has a large number of offspring.

    1. Low survivorship

13. It is usually short-lived.

    1. Low survivorship

14. Expects a large percentage of offspring to reach sexual maturity.

    1. High survivorship

15. Expends almost all bodily energy in creating eggs.

    1. Low survivorship

16. Invests a large amount of energy in parental care.

    1. High survivorship

• Know the types of survivorship curves

• Know how to calculate age class