Demographic Stochasticity Explained
Demographic stochasticity refers to random fluctuations in birth rates, death rates, and the sex ratio within a population. These random events can significantly impact population growth and survival.
Key Impact: Demographic stochasticity poses the greatest extinction risk to small populations. In small populations, random events affecting even a few individuals can disproportionately alter the overall population size, age structure, or sex ratio, potentially leading to decline.
Vulnerability Factors in Populations
Certain population characteristics increase vulnerability to demographic stochasticity:
- Small Geographical Range: A limited area often correlates with a smaller total population size and potentially reduced genetic diversity. Small populations are inherently more susceptible to random demographic events.
- Low Population Density: While seeming counterintuitive, low density within a restricted range can imply a very small number of individuals overall. It can also make finding mates more difficult, exacerbating random effects.
Identifying High-Risk Characteristics
Let's analyze the options based on the principles of demographic stochasticity:
- Option 1: Small geographical range and low population density - This combination strongly suggests a small total population size, making it highly vulnerable to random fluctuations in vital rates (births, deaths, sex ratio).
- Options 2 & 4 (Large geographical range): Large ranges can typically support larger populations, which are less affected proportionally by random demographic events.
- Option 3 (Small geographical range and high population density): While a small range indicates potential vulnerability, high density might suggest a larger total population compared to a low-density scenario within the same small range, potentially buffering random effects slightly more.
Therefore, the set of characteristics most likely to cause population extinction via demographic stochasticity is a small total population size, indicated by a small geographical range and low population density.
Important Questions from Population characteristics
- Consider the following strains of an influenza virus and their basic reproduction numbers ($R_0$). Assuming that they are all equally virulent, which one of the following strains would be most concerning for a completely vulnerable population of humans?
- What is the relationship between effective population size ($N_e$) and total population size ($N$) of any naturally occurring eukaryotic population?
- The effective population size of a sexually reproducing, diploid, animal species will be highest when the sex ratio (number of reproducing males / number of reproducing females) is
- Which of the following plots describes the expected relationship between population size (y-axis) and generation time (x-axis) in vertebrates? Here, each data point represents a different vertebrate species and the generation time is defined as the average interval between two generations.
- A population of birds has a 3:2 male to female adult sex ratio at the beginning of the breeding season. During the breeding season, every female produces 8 eggs of which 4 survive to become juveniles. A census at the end of the breeding season accurately estimates the bird population to be 1300 individuals. Assuming no deaths, the number of adult males in this population is ______ individuals.
