Explain the risks to a species if its population size decreases, reducing genetic variation (knowledge of genetic drift is not required)

SouravNovember 15, 2024

Answer

A decrease in population size can have significant implications for a species, particularly in terms of reducing genetic variation. Here are the key risks associated with this phenomenon:

1. Increased Vulnerability to Extinction

As population sizes decline, species become more susceptible to extinction due to several interrelated factors:

• Inbreeding Depression: Smaller populations often experience inbreeding, which reduces genetic diversity. This leads to the expression of deleterious alleles and can result in lower fitness, reduced reproductive success, and increased juvenile mortality rates. Over time, inbreeding can severely compromise the health of individuals within the population.
• Demographic Stochasticity: Small populations are more affected by random events that can lead to fluctuations in population size. For example, a single disease outbreak or environmental change can have catastrophic effects on a small group, potentially leading to extinction.

2. Reduced Adaptability to Environmental Changes

Genetic variation is crucial for a population’s ability to adapt to changing environmental conditions:

• Limited Adaptive Potential: A reduction in genetic diversity limits the range of traits available for natural selection to act upon. This makes it difficult for populations to adapt to new challenges such as climate change, habitat loss, or emerging diseases. Without sufficient genetic variation, populations may lack the necessary traits to survive in altered environments.
• Failure to Cope with Stressors: Populations with low genetic diversity often exhibit reduced resilience when faced with environmental stressors. This can include increased susceptibility to diseases and parasites, as well as challenges posed by climate variability.

3. Loss of Ecosystem Functionality

The decline of a species can have broader ecological implications:

• Disruption of Ecological Roles: Each species plays a specific role within its ecosystem, contributing to processes such as pollination, seed dispersal, and nutrient cycling. A decline in population size can disrupt these functions, leading to cascading effects within the ecosystem. For instance, the loss of keystone species can alter habitat structure and affect numerous other organisms.
• Decreased Biodiversity: As species become endangered or extinct, overall biodiversity declines. This loss diminishes ecosystem stability and resilience, making ecosystems more vulnerable to further disturbances and degradation.

4. Impacts on Genetic Health

The health of a population is closely tied to its genetic diversity:

• Reduced Fertility and Viability: Low genetic diversity can lead to decreased fertility rates and poor offspring survival. For example, studies have shown that populations with limited genetic variation often produce fewer viable offspring due to factors like reduced sperm quality and lower litter sizes.
• Increased Disease Susceptibility: Populations with diminished genetic diversity are generally less able to resist diseases and parasites. This vulnerability can lead to higher mortality rates during disease outbreaks, further exacerbating population declines