5-Population Ecology 2

Population Ecology 2: Population Regulation and Fluctuation

• A world map displays average annual population growth rates (1997-2015).
• Projections are based on 1980-1997 fertility rates and 1997 age-sex population structures.
• Regions show varying growth rates, from less than 0.0% to over 2.0%.
• Data is not available for some areas.

McCarty Woods Restoration

• Restoration event scheduled for November 17, 2023, from 9:00 am to 10:30 a.m.
• Meeting location: Northeast corner of the parking lot.

McCarty Woods Restoration Project: November 17

• Volunteers receive a free t-shirt (first 100).
• The logo of the project is recognizable and included.

Population Growth Models

• Students need to understand exponential and logistic population growth models and their assumptions.
• Using population growth equations to determine future population size is crucial.
• It is essential to contrast biotic and abiotic factors controlling population sizes, along with defining and recognizing density-dependent and independent population controls.
• Learning about the lynx and snowshoe hare population cycles is vital.

Basic Population Growth Model*

• The model ignores migration in and out of a population.
• Population size change (ΔN/ΔT) equals birth rate (B) minus death rate (M).

Multiplicative Population Growth

• Population growth is not additive; it is multiplicative.
• If a population of 100 has 50 females each having 1 baby, and no deaths, the second generation is 150 individuals.

Per Capita Birth Rate

• Birth rates are expressed per individual (per capita).
• Per capita birth rate (b) = Births (B)/ Population size (N).
• Example: If 500 elephants are born in a population of 1000 elephants, then the per capita birth rate is 0.5.

Per Capita Death Rate

• Death rates are also expressed per individual (per capita).
• Per capita death rate (m) = Deaths (M)/ Population size (N).

Population Growth Rate (r)

• Combining birth and death rates results in the population growth rate (r).
• Population growth equation (Eq. 1) on a per capita basis is: ΔN/ΔT = bN - mN
• Per capita rate of increase (r) = b - m
• Population growth equation (Eq. 3) is: ΔN/ΔT = rN

Exponential Population Growth

• The exponential model describes population growth in an idealized environment (unlimited resources, no competition).
• ΔN/ΔT= rN
• Assuming unlimited resources, the growth rate (r_max )is constant, but the number of individuals changes over time.

Can Exponential Growth Go On Forever?

• No, exponential growth cannot continue indefinitely.
• Resources and competition limit populations and stop growth.
• Elephants in Kruger National Park, South Africa, illustrate this phenomenon.

A More Realistic Population Growth Model: Logistic Growth

• A more realistic population model limits growth by incorporating carrying capacity (K).
• Carrying capacity (K): maximum population size the environment can support.

Logistic Growth Model

• Logistic model = exponential model + carrying capacity term
• dN/dt = r_maxN * (K-N)/K
• The growth rate (r) decreases as the population approaches K.
• When N=0, (K-N)/K = 1; when N=K, (K-N)/K = 0.

Logistic Growth Model: Example

• A hypothetical example illustrates logistic growth.
• Factors influencing population growth (intrinsic rate of increase, population size) and calculations are displayed in the table.

Density Dependence in Biotic Factors

• Biotic factors (parasitism, disease, predation, competition), often affect population size based on density.
• Birth and/or death rates change with changing density.
• Density-dependent examples include clutch sizes of song sparrows and seed production of Sanicula plants.

Density Independence in Abiotic Factors

• Abiotic factors (fire, flood, hurricane, drought), often affect population size regardless of density.

Population Fluctuations and Cycles

• Many populations fluctuate or cycle, showing regular changes between high and low population sizes.
• Examples include the snowshoe hare and lynx population cycles.

Human Population Growth

• Well-approximated by the exponential model, unusual compared to other organisms in nature.
• Current population is about 8 billion.
• Predicted population in 2025 is 8.2 billion.
• Although population is growing, the rate of increase is decreasing.

Ecology in the News...

• Parasites can affect animal behavior, like the parasite Toxoplasma gondii in rats.
  • A common protozoan parasite found in rats.

This quiz covers key concepts in population ecology, focusing on population regulation and fluctuation. Students will explore population growth models, including exponential and logistic growth, and analyze factors that influence population sizes. Prepare to enhance your understanding of ecological dynamics and restoration efforts.