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Species interactions: the BIG experiment

Species interactions: the BIG experiment

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IMG_8377 banana slug adj.jpg
BIG experimnt site in Costa Rica; photo HeatherSlinn
map of seed predation transects, BIG experiment
Arctic Yukon Kluane BIG experiment seed predation
the BIG (Biotic Interaction Gradients) Experiment

One of Darwin's many ideas was that interactions between species – like competition and predation – are stronger and therefore more important in tropical and lowland ecosystems. Until recently however, evidence for large-scale patterns in the intensity of species interactions was contradictory, and cobbled together from many small-scale studies using different methods.


The goal of the BIG experiment is to test geographic patterns in the intensity and effects of species interactions using simple, standardized experiments conducted at massive geographic scales. To do this I collaborate with a network of fantastic biologists working in >10 countries spanning the Americas.

For Phase 1 of the BIG experiment, we set out more than 7000 small piles of seeds along 18 mountains from Alaska to Ecuador, and checked them the next day to see how many were eaten.

We showed that even after only 24 hours, seed predation more than doubles from the arctic to equator and from 4000 meters elevation (high in the Andes) to sea level (Science Advances eaau4403).

NOTE: in late 2021 we made an important correction to the original article. After fixing a mistake in the coding of the response variable in our binomial GLMModels, the latitudinal and elevational declines in seed predation are twice as strong as originally reported. The PDF on the Science Advances webpage is the corrected version

We also showed that these large-scale patterns are driven by the smallest seed predators: high predation in the tropics and lowlands is caused mostly by insects and other invertebrates. Thus a relatively underappreciated group of animals likely plays an outsized role in the ecology and evolution of our most biodiverse ecosystems.

Media coverage:

ScienceTrends summary

Radio Canada article (french)

Prince George Daily News article article

Phase 2 of the project is extending to mountains farther inland in the Americas and down toward the south pole, exploring the factors that drive the strength of species interactions.

Media coverage:

McGill tribune article

Phase 3 is in the planning stages and data collection should start June 2020. Collaborators from any continent are welcome - please get in touch if you would like to be involved!

High elevation site, Argentina
seeds, ants, seed predation, Baja, BIG experiment