Population Regulation and Competition

Definition: Intraspecific competition refers to the interaction between individuals of the same species, which is detrimental to both participants.
Effects on Population Density:
- Population density is regulated by competition for resources.
- Initially affects the quality of individual life, followed by growth and reproduction.

Scramble Competition:
- Occurs when growth and reproduction are depressed equally across all individuals as competition intensity increases.
- This can lead to local extinction if resources are insufficient for all individuals.
Contest Competition:
- Takes place when certain individuals claim enough resources while denying others a share.
- Only a fraction of the population may suffer; those accessing the resources can maintain population sustainability.
- intensity of intraspecific competition typically increases with population density, initially affecting growth and development and later individual survival and reproduction.
- As resource availability declines for all individuals, their intake must decrease, leading to slowed growth and development.

the inverse relationship between population density and individual growth

Study by J.N. Chatworthy (Oxford University):
- Examined growth of white clover plants (Trifolium repens) at different population densities.
- Results showed an inverse relationship between growth rate (mean weight/plant) and population density (image linked in transcript).
Study by Li-Wen Wang (Ohio University):
- Investigated effects of intraspecific competition on growth and photosynthesis of Atriplex prostrata at varying densities.
- Results demonstrated an inverse relationship between plant density and individual growth metrics (mean plant weight, mean leaf area, leaf area ratio, net photosynthesis).

Reduced Survival with High Density:
- High population density often leads to decreased survival rates. Mortality can increase resource availability for remaining individuals, enhancing their growth.

Definition: Self-thinning refers to the progressive decline in density and increase in growth (biomass) of remaining individuals due to:
- Density-dependent mortality
- Population growth.

Grain (or seed) production decreases when plants are grown at higher densities, demonstrating density-dependent fecundity effects.

Carrying Capacity (K):
- Represents the maximum sustainable population size for a given environment.
- Example for Monroe County, WV:
- Exponential growth period from 1800-1850 with growth rate r = 0.074.
- Logistic growth carrying capacity K = 13200.

The rate of growth is described by the equation:
\frac{dN}{dt} = rN\left(\frac{K-N}{K}\right)
Growth Dynamics:
- When population (N) is smaller than carrying capacity (K), it increases rapidly. The growth rate is greatest at the inflection point, where N = K/2. The growth rate diminishes as N approaches K.

Definition: Interspecific competition negatively impacts the populations of two or more species through different interaction types.
competition is regarded as the major force behind species divergence and specialization
Forms of Interspecific Competition:
- Exploitation Competition: Occurs through indirect interactions affecting resource availability.
- Interference Competition: Involves direct interactions where individuals prevent others from accessing resources.

Population Interactions (Table Example):
- Neutral: (0, 0)
- Mutualism: (+, +)
- Commensalism: (+, 0)
- Competition: (-, -)
- Amensalism: (-, 0)
- Predation: (+, -)
- Parasitism: (+, -)
- Parasitoidism: (+, -)

Competition: A (-, -) interaction detrimental to both species.
Amensalism: A (-, 0) interaction where one species negatively affects another without mutual response.
Predation: (+,-) interaction where one species (predator) benefits at the expense of another (prey) by consuming members
Parasitism: (+, -) interaction where one species (the parasite) feeds on another (the host) without intention to kill it.
Parasitoidism: (+,-) the species of parasite kills the host
Mutualism: A (+, +) relationship where both species benefit, which can be either obligatory (essential for survival of both pop.) or non-obligatory (not essential for survival of either).
commensalism: (+,0) one species maintains or provide condition for the welfare of another but does not affect its own well being

Allelopathy: Production of chemicals by one species that inhibit the growth of others, reducing competition.
Coexistence: Occurs when species share a habitat, often using niche separation to partition resources.

States that “complete competitors” cannot coexist - ecological requirements of two species must completely overlap, making one more successful in the given niche.

Fundamental Niche: The full range of environmental conditions and resources that a species can utilize.
Realized Niche: The portion of the fundamental niche actually exploited by a species.
Niche Overlap: Occurs when multiple organisms use a resource simultaneously, leading to competition for that resource.

Competitive release occurs when a species expands its niche after the removal of a competitor or invades unoccupied habitats. The distribution of Typha shows this phenomenon.

For Species 1:
dN1/dt=r1N1(K1−N1−αN2)
- where (\alpha) = competitive impact of species 2 on species 1.
For Species 2:
dN2/dt=r2N2(K2−N2−βN1)
- where (beta) = competitive impact of species 1 on species 2.

Intraspecific competition is detrimental to individuals within a species, affecting growth and reproduction.
There are two competition types: scramble and contest, with different impacts on the population.
The carrying capacity (K) illustrates maximum sustainable population levels, where growth slows as the population approaches K.
Interspecific competition affects multiple species adversely, influencing niche usage based on the scope of mutual resource competition.