Redding Ecology Bio 1111 Clemson University Chapter 53

What is a population?

A group of individuals of the same species living in the same area at the same time that are able to interbreed

What is population ecology?

The study of how populations change over time and space, and how they interact with their environment

Why is it important?

• Conservation (e.g. endangered species)

• Managing fisheries, pests, and diseases

• Understanding human population trends

What is the link between populations and evolution by natural selection?

Populations evolve, not individuals. Natural selection acts on variation within populations, shaping traits over generations.

Population density vs. distribution

• Density: Number of individuals per unit area.

• Distribution (dispersion): How individuals are spaced out (clumped, uniform, random).

Clumped dispersion

(most common): Resources are patchy, social behaviors (e.g. schools of fish).

Uniform dispersion

Driven by competition (e.g. nesting birds, territorial plants).

Random dispersion

(least common): No strong interactions or resource patterns.

Abiotic

Influence habitat suitability.

Biotic

influence habitat suitability.

Causes of population increase

Births and imigration

Causes of population decrease

deaths and emigration

Exponential growth pattern

Rapid growth under ideal conditions

Logistic growth pattern

A growth pattern that occurs when a population's growth rate slows as it approaches its carrying capacity, resulting in an S-shaped curve.

Boom-bust cycles

fluctuations in population size marked by periods of rapid growth followed by sharp declines.

Survivorship

• Proportion of a cohort (same-aged group) surviving to a certain age.

• Survivorship curves show this graphically.

Survivorship curves type 1

High early survival, drops at old age (e.g. humans)

Survivorship curves type 2

Constant death rate (e.g. birds)

Survivorship curves type 3

High early mortality, few survivors live long (e.g. insects, plants)

Survivorship curves x-axis

age

Survivorship curves y-axis

survivors

Basic population size formula

Population size = Births - Deaths + Immigration - Emigration.

Exponential growth formula

A model representing ideal population growth in an environment with unlimited resources, expressed as dN/dt = rN, where N is population size, r is the intrinsic growth rate, and t is time.

Lag phase

Exponential graphs- the initial period where the growth rate is slow as the population acclimates to its environment before accelerating.

What is logistic growth?

A model of population growth that starts slowly, accelerates, and then levels off as resources become limited, often depicted as an S-shaped curve.

What is the formula for the logistic growth model?

The formula for the logistic growth model is expressed as dN/dt = rN(1 - N/K), where N is the population size, r is the intrinsic growth rate, and K is the carrying capacity of the environment.

At what N values does the population grow slowest and fastest (not the actual numbers but the relative size of N. ie.) big, small, in between relative to ______)?

K (carrying capacity)

what does a logistic growth chart look like?

S-curve

What are the three ways that population growth can slow?

1. Reduced birth rate

2. Increased death rate

3. Increased emigration

Define density-dependent factors and give examples

Density-dependent factors are influences on population growth that change in intensity as a function of population size. Examples include competition for resources, predation, and disease.

What is intraspecific competition

Intraspecific competition refers to the competition among individuals of the same species for limited resources such as food, space, and mates. This type of competition can limit population growth and lead to resource depletion.

how does intraspecific competition influence density-dependent factors?

Intraspecific competition influences density-dependent factors by increasing competition for limited resources as population density rises, which can result in reduced birth rates and higher mortality when resources become scarce.

Is predation an intraspecific interaction? 

No, predation is an interspecific interaction, involving competition between different species for resources.

What is the Boom-Bust Cycle and how does it relate to predation?  Why does neither of the species involved get wiped out?

The Boom-Bust Cycle refers to the fluctuations in population sizes of predator and prey species, where the predator population increases following an increase in prey, leading to a subsequent decline in prey population due to over-predation. Neither species gets wiped out because as the prey population decreases, it results in reduced food availability for predators, causing their numbers to decline, which then allows the prey population to recover.

Define density-independent factors and give examples

Density-independent factors are environmental factors that affect population size regardless of population density, such as natural disasters, climate change, or human activities. Examples include floods, droughts, and wildfires.

What are life history traits?

Life history traits are characteristics that influence an organism's schedule of reproduction and survival, including traits such as age at first reproduction, number of offspring, and lifespan.

Why are fecundity and survivorship inversely related (what are the tradeoffs)?

Fecundity and survivorship are often inversely related due to the trade-offs organisms face in resource allocation; high fecundity typically means that an organism allocates more resources to producing offspring and less to individual survival, resulting in lower survivorship rates for both the parent and offspring.

Distinguish between r-selection and k-selection life history patterns. 

r-selection refers to traits that promote high reproductive rates and rapid population growth in unstable environments, while k-selection emphasizes traits that enhance the survival and competitiveness of individuals in stable environments with limited resources.