Lab Report: Evolution of Finch Beak Size and Population

Categories: Biology


This lab report explores the evolution of quantitative traits, specifically beak size, in finches on Darwin and Wallace Islands. It investigates the influence of various biological and environmental parameters, such as precipitation, heritability, clutch size, and island size, on beak size and population numbers of these finches. The study uses a computational model to simulate changes in finch populations over time and analyzes the results to understand the factors shaping the evolution of beak size and population numbers.


Evolutionary biology involves studying how species adapt to their environments over time.

In this lab, we focus on the evolution of quantitative traits, which are characteristics influenced by multiple genes. Specifically, we examine the beak size of finches inhabiting Darwin and Wallace Islands. Beak size is a crucial trait for finches as it affects their ability to access different types of seeds, which vary in hardness due to the prevailing environmental conditions.

The study aims to understand how different biological and environmental parameters influence the evolution of beak size and population numbers in these finch populations.

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By manipulating parameters and observing the resulting changes, we can gain insights into the mechanisms driving evolutionary adaptations.

Materials and Methods


This lab utilizes a computational model to simulate the evolution of finch populations on Darwin and Wallace Islands. The model allows us to manipulate various parameters and observe their effects on beak size and population numbers.

Experimental Procedure

The experiments in this study involve changing specific parameters within the computational model and running simulations to observe the outcomes.

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The parameters manipulated include initial mean beak size, heritability of beak size, variation in beak size, fitness, clutch size, and island size. Precipitation levels are also modified to investigate the influence of environmental conditions.


The Influence of Beak Size on Finch Population Numbers

In the first experiment, we explored how beak size affects finch population numbers. Darwin's birds had a default beak size of 12mm, while Wallace's birds had a beak size of 28mm. Contrary to our initial hypothesis, both populations experienced an increase in beak size over time. Additionally, the population of both Darwin and Wallace birds grew steadily.

The Influence of Precipitation on Beak Size and Population Numbers

The second experiment examined the effect of decreasing precipitation on Darwin Island. We hypothesized that a decrease in rainfall would result in an increase in beak size and a temporary decrease in population, followed by population growth as finches adapted to the changing conditions. The results supported our hypothesis, as beak size increased, and the population exhibited the expected trend over time.

Subsequent experiments for 200 and 300 years confirmed the initial observations, with both beak size and population numbers following the predicted patterns. Notably, in the 300-year experiment, Darwin's birds eventually surpassed Wallace's birds in both population size and beak size.

Simultaneous experiments on both islands revealed similar trends, with beak size and population numbers increasing as expected over time.

The Influence of Increased Precipitation on Beak Size and Population Numbers

The next experiment investigated the effect of increased precipitation on Darwin Island. It was hypothesized that increased rain would result in smaller, shallower beaks and an overall increase in population. The results aligned with our hypothesis, as beak sizes decreased, and the population grew substantially.

Repeated experiments for both islands showed that Wallace Island birds also experienced similar trends in beak size and population growth in response to increased precipitation.

The Influence of Island Size on Beak Size and Population

In this experiment, island size was manipulated. Darwin Island's size was increased to 1km, leading to an increase in beak size and population numbers. Conversely, decreasing island size caused initial population drops, followed by population growth.

The Effect of Clutch Size and Heritability

Previous experiments indicated that decreasing clutch size and heritability led to a significant decrease in finch populations, potentially to the point of extinction. These parameters play a crucial role in population dynamics and adaptation.


The results of these experiments shed light on the complex interactions between biological and environmental factors in shaping the evolution of finch populations. Beak size, a quantitative trait, exhibited plasticity in response to changing conditions, contrary to our initial expectations. Both Darwin and Wallace Island birds adapted to their environments by altering their beak sizes, and populations increased over time.

Precipitation levels played a significant role in determining the availability of seed types, influencing beak size evolution. Increased precipitation favored smaller beaks for soft seeds, while decreased precipitation led to larger beaks suitable for hard seeds. These adaptations allowed finches to optimize their foraging efficiency and survival.

Island size also affected beak size and population dynamics, with larger islands supporting larger beaks and populations. This highlights the importance of habitat size in species evolution and survival.

Additionally, clutch size and heritability emerged as critical factors in population maintenance. Reduced clutch size and heritability could lead to severe population declines, emphasizing the importance of genetic diversity and reproductive strategies in population survival.


This study demonstrates the dynamic nature of finch populations in response to changing environmental and biological parameters. Beak size, a quantitative trait, showed remarkable adaptability over time, allowing finches to thrive in diverse conditions. Precipitation, island size, clutch size, and heritability all played vital roles in shaping the evolution and survival of these populations.


The findings of this research highlight the significance of conserving diverse habitats and maintaining genetic diversity within populations. Conservation efforts should consider the complex interactions between environmental factors and genetic traits, aiming to protect the adaptability and resilience of species in the face of environmental changes.

Further research could explore additional factors influencing the evolution of quantitative traits and their implications for species survival. Understanding these mechanisms is crucial for preserving biodiversity and facilitating the adaptation of species to a rapidly changing world.


  • Grant, P. R., & Grant, B. R. (2008). How and Why Species Multiply: The Radiation of Darwin's Finches. Princeton University Press.
  • Schluter, D. (2000). The Ecology of Adaptive Radiation. Oxford University Press.
Updated: Jan 03, 2024
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Lab Report: Evolution of Finch Beak Size and Population. (2018, Sep 12). Retrieved from

Lab Report: Evolution of Finch Beak Size and Population essay
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