Which three factors contributed to the decline and vulnerability of Franklin's bumblebee (Bombus franklini)?

Which three factors contributed to the decline and vulnerability of Franklin's bumblebee (Bombus franklini)?

• A. Overabundant populations, stable environment, high genetic diversity.
• B. Pesticide exposure as the sole cause.
• C. Climate stability and gene flow.
• D. Historically small effective population sizes, environmental instability, and long-term reduced genetic diversity.

Answer: (C)

The main idea is that a combination of small population size, environmental variability, and loss of genetic diversity makes a species extremely vulnerable to decline. When a population has historically been small, genetic drift can quickly reduce genetic variation and increase inbreeding, which lowers fitness and the ability to adapt. If the environment is unstable over time, the population faces repeated bottlenecks and resource fluctuations, pushing numbers up and down and heightening extinction risk. Long-term reduced genetic diversity then leaves little raw material for selection to act on when new challenges arise, such as disease, climate shifts, or changes in available flowering resources. Put together, these factors create a fragile situation for Franklin's bumblebee, making decline and vulnerability likely. By contrast, stable climate and ongoing gene flow between populations would generally help maintain diversity and resilience, and treating pesticide exposure as the sole cause overlooks the broader demographic and genetic pressures at play.

The main idea is that a combination of small population size, environmental variability, and loss of genetic diversity makes a species extremely vulnerable to decline. When a population has historically been small, genetic drift can quickly reduce genetic variation and increase inbreeding, which lowers fitness and the ability to adapt. If the environment is unstable over time, the population faces repeated bottlenecks and resource fluctuations, pushing numbers up and down and heightening extinction risk. Long-term reduced genetic diversity then leaves little raw material for selection to act on when new challenges arise, such as disease, climate shifts, or changes in available flowering resources. Put together, these factors create a fragile situation for Franklin's bumblebee, making decline and vulnerability likely. By contrast, stable climate and ongoing gene flow between populations would generally help maintain diversity and resilience, and treating pesticide exposure as the sole cause overlooks the broader demographic and genetic pressures at play.