Island Rule in Vertebrates

ISEF Category: Animal Sciences

Subcategory: Systematics and Evolution  ·  Difficulty: Advanced  ·  Setup: University Lab  ·  Time: Full Year

The Hook

On islands, evolution can act like a budget cut. Big animals can shrink, and small animals can grow, because food, predators, and space all change the rules. You can test that pattern with real data instead of waiting for a field trip to a remote island.

What Is It?

The island rule is the idea that vertebrates often change body size after they live on islands. Large species may become smaller, which scientists call dwarfism. Small species may become larger, which scientists call gigantism. Think of an island like a tiny apartment building, where limited space and resources push animals toward a different size than their mainland relatives.

A phylogenetic comparative model adds a family tree to the analysis. That matters because close relatives can look alike simply because they share ancestry, not because they faced the same island pressures. By accounting for relatedness, you can ask whether island life still predicts body size change after you control for evolution history. That turns the project into a real test of an old idea in biogeography.

Why This Is a Good Topic

This is a strong science fair topic because you can test a classic evolution pattern with data that already exist. You do not need to catch animals or build a wet lab setup. The project connects to island biogeography, conservation, and how species respond to isolation, and it teaches you data cleaning, model choice, and statistical thinking.

Research Questions

• How does body mass change between island vertebrates and their mainland relatives? ?
• What is the effect of vertebrate class on the direction and size of island dwarfism or gigantism? ?
• Does island area predict the strength of body-mass change after phylogenetic correction? ?
• To what extent does island isolation change the odds that a species evolves dwarfism or gigantism? ?
• Which taxonomic groups show the clearest island-rule signal after controlling for shared ancestry? ?
• How does the island rule change when you compare only endemic island species with island mainland sister pairs? ?

Basic Materials

• Laptop or desktop computer with internet access.
• Spreadsheet software such as Google Sheets or Microsoft Excel.
• Reference manager such as Zotero for tracking sources.
• Public body-mass datasets and species trait tables from journals, museum databases, or open repositories.
• Notebook or digital document for recording species matches, exclusions, and model notes.

Advanced Materials

• Laptop or desktop computer with enough memory for large trees and datasets.
• R and RStudio for phylogenetic analysis.
• Access to university library databases for full-text papers and trait sources.
• External storage or cloud backup for raw data and scripts.
• Access to a mentor or statistician for checking model assumptions.

Software & Tools

• R: Fits comparative models, cleans trait data, and runs sensitivity tests.
• RStudio: Gives you a clean workspace for scripts, plots, and reproducible analysis.
• Zotero: Tracks sources, species papers, and dataset citations.
• Google Sheets: Helps you screen records, flag missing values, and build codebooks.
• phytools: Adds tree-based functions for ancestral state and body-size analysis.

Experiment Steps

1. Define the comparison framework you will use, such as island versus mainland pairs, clade-wide summaries, or both.
2. Assemble and clean the trait table so every species has a verified mass, island status, and taxonomic label.
3. Match each species to a phylogenetic tree and decide how you will handle missing taxa and uncertain placements.
4. Choose the comparative model that tests the island effect while controlling for shared ancestry and body size.
5. Plan your sensitivity checks, including alternative datasets, outlier rules, and model comparisons.
6. Design your output figures so the final story shows effect size, uncertainty, and group-level differences.

Common Pitfalls

• Mixing juvenile and adult mass values, which can make island species look smaller or larger for the wrong reason.
• Comparing island species with unrelated mainland species, which blurs the signal from ancestry.
• Leaving taxonomy unstandardized, which splits one species into several names or merges different species by mistake.
• Treating all islands as one setting, which hides the difference between tiny oceanic islands and large continental islands.
• Fitting one model and stopping, which can make a weak island effect look stronger than it really is.

What Makes This Competitive

A strong version of this project does more than repeat the island rule. It tests whether the pattern holds after phylogenetic correction, then checks whether island area, isolation, or vertebrate group changes the effect. If you compare several model forms and report effect sizes with uncertainty, you move from a class summary to real comparative biology.

Project Variations

• Test the island rule within one vertebrate group, such as only birds or only reptiles, to see whether the pattern holds inside a single clade.
• Compare oceanic islands with continental islands to see whether isolation strength changes the size shift.
• Use log body mass instead of raw mass and compare several phylogenetic model types to see how model choice changes the conclusion.

Learn More

• PubMed: Search review articles on island biogeography, dwarfism, gigantism, and phylogenetic comparative methods.
• Open Tree of Life: Use the tree browser and downloads to match species names to a phylogeny.
• NCBI Taxonomy: Check accepted species names, synonyms, and higher classifications.
• CRAN package documentation for ape, phytools, and caper: Read official vignettes and examples for comparative analysis in R.
• NOAA National Centers for Environmental Information: Find island climate and geography data when you want to add environmental context.