Question

Toucans disperse seeds of key forest species such as juçara palms by eating the fruit and defecating the seeds in new locations, sometimes more than a kilometer away. If there are no toucans, is the genetic diversity of palms likely to increase or decrease within forest fragments (and why)? a. increase (due to increased genetic drift) b. decrease (due to decreased gene flow) c. decrease (due to decreased mutation rate) d. decrease (due to decreased natural selection)

Short answer

The genetic diversity of palms is likely to decrease in the absence of toucans due to decreased gene flow. Without toucans to disperse the seeds, there are fewer opportunities for gene flow among palm populations in different locations.

Step-by-step solution

Understand the given information

Toucans play a significant role in seed dispersal, as they consume the fruits of palm trees and defecate the seeds in new locations, which allows the palms to grow in different areas. This process is essential for maintaining genetic diversity within the forest.

Define genetic diversity

Genetic diversity is the variety of genes within a population or species. It is essential for maintaining the health and survivability of a species, as greater genetic diversity allows a population to better adapt to environmental changes.

Analyze the impact of no toucans

If there are no toucans, the seed dispersal process will not take place effectively. The palm species will not have their seeds spread across the forest, which can have a significant impact on genetic diversity. Now review the given options: a. increase (due to increased genetic drift) - Genetic drift is the change in allele frequencies within a population due to random events. In this case, the absence of toucans would not lead to increased genetic drift, so this option is incorrect. b. decrease (due to decreased gene flow) - Gene flow is the transfer of genetic information from one population to another. In this case, the absence of toucans would lead to decreased seed dispersal and, thus, fewer opportunities for gene flow among palm populations in different locations. This option seems correct. c. decrease (due to decreased mutation rate) - The absence of toucans would not affect the mutation rate of palms. This option is incorrect. d. decrease (due to decreased natural selection) - Natural selection is the process by which individuals with certain advantageous traits are more likely to survive and reproduce. The absence of toucans would not directly affect natural selection within palm populations. This option is incorrect.

Choose the correct answer

Based on the analysis, the correct answer is: b. decrease (due to decreased gene flow)

Key concepts

Gene Flow

In the context of forest ecosystems, gene flow refers to the movement of genetic material within and between populations of species. Imagine a forest as a bustling city where genes are like commuters traveling to different neighborhoods. Without transportation, like buses and trains—or in our case, seed-dispersing animals—commuters stay put. Similarly, when animals like toucans help to disperse seeds, they're acting like nature's transportation system, moving genetic materials to new areas. This genetic exchange is crucial for maintaining a species' genetic variation.

In a forest fragment without the toucans' assistance, seeds may not reach distant spots, reducing the opportunities for different palm populations to exchange their genetic material. This isolation can lead to a decline in gene flow, which makes natural populations more vulnerable to inbreeding and less able to adapt to environmental changes or resist diseases. Therefore, sustaining a variety of seed dispersers is essential for ongoing gene flow and the genetic health of forest species.

Seed Dispersal

Seed dispersal is a vital ecological process that affects the distribution and genetic diversity of plant species. If we think of seeds as young adventurers setting out into the world, seed dispersal is the stage where they embark on their journey to find a new place to take root. Toucans, with their fruit-based diets, play a key part in this ecological drama. They consume fruits and carry seeds away from the parent plant. Upon defection, the seeds find themselves in new locations with fewer competitors and a potentially different environment.

Without these feathered travelers, seeds might only fall beneath their parent plants, leading to overcrowding and competition among siblings for resources. Resultantly, some plants may fail to thrive or even germinate, reducing the genetic diversity of future generations. Seed dispersal by animals not only helps seeds establish in favorable conditions but also mixes the genetic deck. This mixing increases variation, which is the raw material for natural selection.

Genetic Drift

Genetic drift is like the roll of the dice that randomly influences which genes are passed on to the next generation. It's particularly pronounced in smaller populations where chance events can have a bigger impact on the gene pool. If toucans were missing, seeds wouldn't spread far and wide, leading to smaller, more isolated palm populations. While one might think that small groups can lead to greater fluctuations in gene frequencies, in this scenario, the lack of gene flow actually exacerbates the situation by isolating genetic pools.

Over time, these isolated populations might experience genetic drift that could significantly alter their genetic makeup, potentially reducing their overall genetic diversity and adaptability. The solution, b. decrease (due to decreased gene flow), that students are asked to consider in their textbooks underscores how critical gene flow is in counteracting genetic drift's random nature, thereby maintaining a robust gene pool within the forest ecosystem.

Natural Selection

Natural selection can be likened to the meticulous gardener who cultivates the healthiest, strongest plants, allowing them to thrive and propagate. It is the process by which organisms with traits that offer a survival or reproductive advantage find themselves more likely to pass on their traits to the next generation. The absence of toucans would not directly reduce natural selection within palm populations. Rather, it would limit the variety of environments that the palms' seeds might end up in, indirectly affecting the subsequent selection processes.

Because toucans can no longer carry the seeds to different areas where different conditions might favor different traits, the unique pressures that shape a plant's adaptability are reduced. While natural selection itself isn't diminished by the absence of toucans, the range of conditions and, consequently, the variability in traits that result from these conditions could be. Remember, natural selection requires genetic variation to act upon, and this variation is enriched through processes like gene flow and seed dispersal.