Question 1

What is the difference between density-dependent and density-independent factors?

Accepted Answer

Density-dependent factors, like competition and disease, have an effect that changes with population density—they become more intense as the population grows, helping to regulate it around carrying capacity. Density-independent factors, such as floods or fires, affect populations regardless of density and can cause sudden, unpredictable changes. For example, a drought might kill a fixed proportion of a population, whether it's large or small.

Question 2

How do you calculate population size using mark-release-recapture?

Accepted Answer

The formula is N = (M × C) / R, where M is the number of individuals initially captured, marked, and released; C is the total number captured in the second sample; and R is the number of marked individuals recaptured in that second sample. For instance, if you mark 50 birds, then later catch 80 birds and find 10 marked, the estimated population is (50 × 80) / 10 = 400 birds. Remember that this method assumes no births, deaths, immigration, or emigration between samples, and that marks are not lost or harmful.

Question 3

What is carrying capacity and why is it important?

Accepted Answer

Carrying capacity (K) is the maximum population size that an environment can support sustainably, given the available resources like food, water, and shelter. It's important because it sets a limit on population growth; beyond K, resources become scarce, leading to increased competition, disease, and mortality. Understanding K helps in managing wildlife populations and predicting the effects of environmental changes, such as habitat loss or climate change.

Question 4

How does sustainability relate to population biology?

Accepted Answer

Sustainability in population biology involves using resources at a rate that allows populations to replenish themselves, ensuring long-term availability. For example, maximum sustainable yield (MSY) is the largest harvest that can be taken from a population without causing it to decline. This concept is applied in fisheries management, forestry, and wildlife conservation to balance human needs with ecosystem health. Overexploitation beyond MSY leads to population crashes and loss of biodiversity.

Question 5

What are some real-world examples of population management?

Accepted Answer

One example is the management of North Sea cod fisheries, where quotas are set based on MSY to prevent overfishing. Another is the reintroduction of wolves to Yellowstone National Park, which helped control elk populations and restored ecosystem balance. In agriculture, integrated pest management uses natural predators to control pest populations sustainably, reducing the need for chemical pesticides.

Question 6

Why do populations sometimes overshoot carrying capacity?

Accepted Answer

Populations can overshoot carrying capacity when there is a time lag between population growth and the depletion of resources. For example, if a deer population grows rapidly due to abundant food, they may consume vegetation faster than it can regrow, leading to a crash as food runs out. This overshoot is often followed by a die-off, bringing the population back below K. Such cycles are common in species with boom-and-bust dynamics.

Populations and sustainability

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