Population Growth and Dispersion

Population Growth

• Population Growth: The change in the number of individuals of a species in a defined area over a certain time period.
• Factors limiting growth: Limited resources, competition, predation, and disease.
• Spekboom: Serves as habitat for numerous organisms, forming a dense thicket biome.
• Elephant's impact: Elephants clear spekboom, allowing for movement between biomes.

Population Dispersion

• Distribution of individuals within a geographical area.
• Random: Individuals spread randomly, as in a uniform habitat.
• Clumped: Individuals group together due to patchy resources, social behavior, or reproductive patterns.
• Uniform: Individuals are evenly spaced, often due to competition for limited resources.

Demography

• The statistical study of population changes concerning size, age structure, and sex ratios.
• Used to predict population trends and manage resources.
• Exponential growth: Occurs when a population has high birth rates and low death rates, resulting in a rapid increase in numbers.
• J Curve: A graphical representation of exponential growth.
• Formula: dN/dt=(b−d)NdN/dt = (b-d)NdN/dt=(b−d)N
• r > 0: Population is growing.
• r < 0: The population is decreasing.
• r = 0: Zero population growth.
• South African Rhinos: Used as an example of population growth, highlighting birth, death, and growth rates.
• Poaching impact: Example of how human activity negatively influences a population.

Do Populations Ever Grow Exponentially?

• Exponential growth: Occurs only under ideal conditions, such as unlimited resources.
• Logistic growth: Occurs in environments with limited resources.
• Carrying capacity (K): The maximum population size that a specific environment can support.

Population Growth Under Ideal Conditions

• High birth rates and low death rates.
• r: Represents the maximal per capita growth rate.
• Formula: dN/dt=rmaxNdN/dt = r_{max}NdN/dt=rmax​N

Carrying Capacity

• Population sizes are limited by factors like resource scarcity.
• The maximum number of individuals that can be sustained in a given environment.

Logistic Model

• Per capita growth rate decreases as population size approaches carrying capacity.
• S-shaped curve: Represented graphically.
• Formula: dN/dt=rN(K−N)/KdN/dt = rN (K - N)/KdN/dt=rN(K−N)/K

Intraspecific Competition

• Competition for limited resources between individuals of the same species.
• Animals: Food, water, territories, and nesting sites.
• Plants: Sunlight, water, nutrients, and growth space.
• Results in uniform distribution and increased predation/disease rates.

Exponential vs Logistic Growth

• Density-dependent mortality (logistic): Mortality rates increase with population density due to limited resources, competition, and disease.
• Density-independent effects (exponential): Mortality rates are not affected by population density, often due to catastrophic events.

Population Cycles

• Fluctuations in population size over time influenced by density-dependent and density-independent factors.
• Stable: Relatively constant population size.
• Cyclic: Fluctuations in population size driven by interactions between predator and prey populations.
• Chaotic: Unpredictable fluctuations due to dominant density-independent effects.

Metapopulation Dynamics

• Interconnected populations of the same species that exchange individuals.
• Source population: A population with a surplus of individuals that migrates to other habitats.
• Sub-optimal population: A population with a deficit of individuals that relies on immigration from suitable habitats.
• Unsuitable: Habitats where populations cannot survive for extended periods.

Number of Breeding Seasons

• Iteroparous: Organisms reproduce multiple times throughout their lifespan.
• Semelparous: Organisms reproduce only once in their lifespan, often producing a large number of offspring.
• Agave: A semelparous species that releases seeds once, maximizing survival chances.

r-K Scheme of Life History Strategies

• Different species exhibit distinct life history strategies.
• r-selection: Rapid growth, high reproductive rate, and low parental care.
• K-selection: Slow growth, low reproductive rate, and high parental care.

Population Growth and Age Structure

• Negative growth: Occurs when death rates exceed birth rates, resulting in a shrinking population.
• Rapid growth: Characterized by a high proportion of young individuals, leading to a rapid population increase.

Demographic Transition Model

• Describes the stages of population growth as societies develop.
• Stage 1: Preindustrial, characterized by high birth and death rates.
• Stage 2: Transitional, characterized by declining death rates and stable birth rates.
• Stage 3: Industrial, characterized by declining birth rates and continued low death rates.
• Stage 4: Postindustrial, characterized by low birth and death rates.

Explore the dynamics of population growth and dispersion in this quiz. Understand how factors like resource limitations, competition, and the impact of species such as elephants influence population trends. Test your knowledge on demography and various population distribution patterns.