The depth of a bird’s beak is an important adaptation that allows different species to thrive in their respective environments. The shape and size of a beak determines what food resources a bird can access. Over time, natural selection drives changes in beak morphology to match the food sources available.
In the Gizmo interactive simulation, students can explore how changes to available food sources drive evolution of different beak depths in bird populations. By altering food accessibility, students see first-hand how the depth of finch beaks changed over time.
Background on Finch Beaks
Finches are small perching birds found predominantly in the Galapagos Islands. The Galapagos finches became famous examples of an evolutionary process that adapts animals to their environment. This occurred when the finches colonized the Galapagos Islands that originally lacked animal life. With few competitors, the founding finches were able to diversify and fill vacant ecological niches. This process resulted in the evolution of different finch species with beaks adapted for different diets.
Some key points about Galapagos finch beaks:
– Beak size and shape is strongly linked to diet. Finches with large strong beaks eat nuts and seeds, while finches with slender pointy beaks eat insects.
– The first finches to colonize the Galapagos were believed to have fairly generic beaks able to eat a variety of foods.
– As finch populations grew, competition for resources increased. This drove the emergence of specialized beaks tailored to specific food sources.
– Evolution favors adaptations that allow animals to exploit the available resources. Different beak designs were naturally selected if they improved access to an abundant food supply.
– Changing environmental conditions can alter food availability, triggering evolution of new beak designs better suited for surviving in that habitat.
Using the Gizmo
The Gizmo simulation allows students to explore the evolutionary forces that select for finch beak depth. Students utilize an interactive graph that plots finch populations based on beak depth over several generations.
The simulation begins with two finch populations on an island:
– The original finch population has small generic beaks with an average depth of 10 mm. This allows them to eat all seed types.
– A second finch population migrates to the island. They have large thick beaks with an average depth of 15 mm. These are specialized for eating large hard seeds.
Students can alter conditions on the island by adjusting the:
– Abundance of small soft seeds
– Abundance of large hard seeds
– Chance of wet years (which boosts insect populations)
Based on the conditions, different beak depths will be selected for over time. Students can run the simulation repeatedly and observe how the finch population and average beak depth changes in response.
How Beak Depth Evolves
The key factors that drive evolution of beak depth in the Gizmo are:
1. Abundant food source
Finch populations with beak depths that allow them to eat the most plentiful food source will thrive. Their numbers and genetic prevalence will increase.
For example, if large hard seeds are abundant, finches with deep thick beaks specialized for cracking nuts and seeds will prosper. Over generations, the average beak depth across the whole finch population tends to increase.
2. Competition for resources
When populations grow, competition increases and food availability per finch declines. This selects for beaks better adapted to utilize the remaining food supply. Specialist beaks tailored for the scarcest food become more common.
For instance, if the main food source starts running low, finches with generic beaks cannot survive well. But finches with slim beaks specialized for getting insects can still find food. The finch population’s average beak depth decreases as these specialist thin beaks come to predominate.
3. Environmental changes
Changes to habitat and climate can alter food availability. For example, wet years may boost insects but reduce seeds. This selects for changes in beak proportions suited for the new conditions.
If seeds decline but insects proliferate, the proportion of finches with thin insect-eating beaks will tend to rise. The average beak depth across the whole population will shift lower.
Examples and Results
Here are some examples of how adjusting conditions in the Gizmo can affect evolution of finch beak depth:
Example 1
Starting conditions:
– 50% small soft seeds
– 50% large hard seeds
Results after 20 generations:
– Average beak depth is 12-13 mm
– Finch population consists of a blend of generic and specialist beaks
Example 2
Starting conditions:
– 10% small soft seeds
– 90% large hard seeds
Results after 20 generations:
– Average beak depth increases to 14-15 mm
– Large hard seed specialists predominate
Example 3
Starting conditions:
– 10% small soft seeds
– 10% large hard seeds
– 80% chance wet years
Results after 20 generations:
– Average beak depth decreases to 8-10 mm
– More finches have slender insect-eating beaks
Conclusion
The Gizmo simulation highlights the evolutionary interplay between beak morphology, food availability, and natural selection. Students get to alter conditions and witness first-hand how changes in habitat and resources drive adaptation of beak depth over generations.
Key takeaways include:
– Beak depth evolves to match the most readily available food source.
– Competition selects for specialist beaks adapted for underutilized niches and scarce resources.
– Environmental changes that alter food abundance will reshape the proportions of different beak types.
– Given enough time, natural selection will drive the evolution of beak designs optimized for utilizing the food sources in that environment.
By completing the Gizmo exercise, students gain an intuitive feel for these evolutionary dynamics and how they transform populations over time. The activity provides an interactive way to visualize and understand the forces that sculpted the iconic finch beaks of the Galapagos.
References
Source | Key Points |
---|---|
Grant, P. R. (1999). Ecology and Evolution of Darwin’s Finches. Princeton University Press. | Seminal research on Galapagos finches documenting how changing environmental conditions drove the evolution of different beak shapes. |
Lamichhaney, S., Berglund, J., Almén, M. S., Maqbool, K., Grabherr, M., Martinez-Barrio, A., Promerová, M., Rubin, C.-J., Wang, C., Zamani, N., Grant, B. R., Grant, P. R., Webster, M. T., & Andersson, L. (2015). Evolution of Darwin’s finches and their beaks revealed by genome sequencing. Nature, 518(7539), 371–375. https://doi.org/10.1038/nature14181 | Modern genomic analysis of Galapagos finches supporting that changes in beak shape genes drove adaptations specialized for different food sources. |
Abzhanov, A., Protas, M., Grant, B. R., Grant, P. R., & Tabin, C. J. (2004). Bmp4 and Morphological Variation of Beaks in Darwin’s Finches. Science, 305(5689), 1462–1465. https://doi.org/10.1126/science.1098095 | Key developmental biology research identifying the gene BMP4 as a major controller of beak depth and shape in finches. |