Problem 9 - Biology Today and Tomorrow with Physiology

Question

A fire devastates all trees in a wide swath of forest. Populations of a species of tree-dwelling frog on either side of the burned area diverge to become separate species. This is an example of __________.

Step-by-Step Solution

Answer

This is an example of allopatric speciation.

Step 1: Understanding the Scenario

In this scenario, a fire destroys trees in a large area of a forest, creating a physical barrier between two populations of tree-dwelling frogs that live on either side. This separation prevents the frogs from interbreeding.

Step 2: Define Key Terms

When a physical barrier like the burned forest area prevents two populations of a species from interbreeding, they may evolve independently over time. If the differences become significant enough, this process may lead to the formation of new species.

Step 3: Identifying the Biological Concept

This process of new species formation due to geographic isolation and subsequent divergence is known in biology as allopatric speciation.

Step 4: Matching the Concept to the Scenario

The example describes a classic case of allopatric speciation, as the physical separation by the burned area results in the divergence of the frog populations into separate species.

Key Concepts

Geographic Isolation

Geographic isolation occurs when a physical barrier separates members of a species into distinct groups. These barriers can be natural, such as mountains, rivers, or burned forest areas, as seen in our tree-dwelling frog scenario. Such isolation prevents gene flow between the populations, as individuals cannot cross the barrier to breed with those on the other side. This interruption in gene exchange is critical because it leads each group to become genetically distinct over time.

Geographic isolation is often the first step in a larger process that can ultimately lead to the formation of new species. It creates an environment where separate populations can adapt to their unique surroundings, experimenting with different mutations and adaptations that might improve survival in their specific enclave. The fire in our example provides a classic illustration, as it effectively places a boundary between frog populations, setting the stage for species divergence.

Species Divergence

Species divergence is the subsequent step when geographically isolated populations start to evolve independently. Without regular gene flow, each group begins to adapt to its specific environmental pressures and challenges. Over generations, these adaptations accumulate, causing the populations to diverge genetically.

This divergence can manifest through:

• Changes in physical characteristics (morphology)
• Variations in reproductive behaviors
• Differences in habitat preferences
• Shifts in dietary habits

These changes are crucial as they allow each populations to exploit their environments more effectively. In our example, once geographic isolation has taken place due to a forest fire, the frog populations face different selective pressures on either side, leading them to evolve along separate paths. This divergence increases over time, pushing the populations further apart genetically.

New Species Formation

The eventual outcome of geographic isolation and species divergence is often the formation of new species, a process known as allopatric speciation. As genetic differences continue to pile up, the once similar groups can become so distinct that they can no longer interbreed, even if the physical barrier is removed. This reproductive isolation is a key criterion for the definition of species in biology.

New species formation doesn't happen overnight but requires numerous generations. What began as a mere separation evolves into complete genetic and reproductive divergence, resulting in new species. In the frog scenario, over time, the populations on either side of the burned area may accumulate enough genetic differences to become reproductively incompatible. Thus, even if the forest grows back, the frogs on either side might not recognize each other as potential mates, confirming the creation of separate species.