Population Ecology Flashcards

Population Ecology

Concept 53.1: Understanding Populations: Density, Spread, and Stats

• A population is all the members of a single species living in a specific area.

• We describe populations by noting their borders and how big they are. Density (how many individuals in an area) and dispersion (how they're spread out) are key things to look at.

How We Count Populations

• We use different counting tricks to guess how many individuals are in a population.

• These can involve counting a few small areas and guessing for the whole area, looking at signs of population size (like nests), or using "mark-recapture."

• Mark-Recapture Method:

  • We catch a few individuals, tag them, and let them go. Later, we catch more individuals and see how many we already tagged. This helps us estimate the total population size (N) using the formula: \frac{N}{s} = \frac{n}{x}

    • s = initial captured, tagged, and released

    • n = individuals captured in the second sample

    • x = recaptured individuals

How Individuals Spread Out

• Where individuals live depends on the environment and how they interact with each other.

• We see three main patterns:

  • Clumped: Individuals gather in groups (e.g., herds).

  • Uniform: Individuals spread out evenly (e.g., plants competing for resources).

  • Random: Individuals are scattered unpredictably.

Population Stats and Life Stories

• Demography is the study of a population's vital stats, like birth and death rates, and how they change.

• Life Table: This table summarizes how likely individuals are to survive at different ages.

• Survivorship Curves: These curves take data from life tables and show the number of individuals still alive at each age.

How Fast Populations Reproduce

• We usually focus on the females in a population because they produce the offspring.

• Reproductive Table (Fertility Schedule): This table summarizes how many offspring females of different ages are likely to have.

Concept 53.2: How Populations Grow: The Exponential Model

• Populations can grow super fast when conditions are perfect (lots of food, space, etc.). This is exponential growth.

• We can describe it with the equation: \frac{dN}{dt} = r_instN

Concept 53.3: How Populations Grow: The Logistic Model

• Realistically, environments can only support a certain number of individuals. This is the carrying capacity (K).

• The logistic growth model takes this into account:
  \frac{dN}{dt} = r_instN(\frac{K-N}{K})

• When the population is small compared to the carrying capacity, it grows fast.

• When the population is close to the carrying capacity, it grows slowly.

• When the population reaches the carrying capacity, it stops growing.

Life's Strategies

• Semelparity: Some species reproduce once in their life and then die (big-bang reproduction).

• Iteroparity: Other species reproduce multiple times.

• If the environment is unpredictable, it favors semelparity. If it's dependable, it favors iteroparity.

Choosing Traits: Density Matters

• K-selection (density-dependent): When a population is near its carrying capacity, traits that help individuals survive and reproduce in crowded conditions are favored.

• r-selection (density-independent): In less crowded populations, traits that allow for quick reproduction are favored.

Concept 53.5: What Limits Population Growth? Density-Dependent Factors

• Density-independent populations: Birth and death rates don't change based on population size.

• Density-dependent populations: Birth rates go down and death rates go up as the population gets more crowded.

What Affects Population Size?

• Competition for resources, diseases, predators, internal body factors, waste buildup, and claiming territory.

Metapopulations: Populations of Populations

• These are groups of smaller populations that are linked together by individuals moving between them.

• If a local population dies out, it can be recolonized by individuals from another population.

How Humans are Growing

• Zero population growth can happen when birth and death rates are both high or both low.

• Demographic transition: This is when a population shifts from high birth and death rates to low birth and death rates.

• Age structure: How many individuals are in each age group affects how the population will grow in the future.

How Many Humans Can Earth Hold?

• It's hard to say exactly how many humans the Earth can support.

• Ecological footprint: This is a calculation of how much land and water each person (or a whole nation) needs to live.