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Animal diversity is driven by global precipitation patterns

Ever since Charles Darwin found an intriguing family of finches in the Galapagos, a question about animal diversity has persisted: Why is there an abundance of species in some places on Earth and a scarcity in others? 

A recent study led by Utah State University has unlocked a new piece of this puzzle. 

Animal diversity 

By utilizing an expansive dataset of global-scale climate information and employing an innovative approach, the researchers have pinpointed certain factors that seem to play an important role in determining animal diversity.

The research indicates that the dietary habits of animals, coupled with the climate conditions of their habitats, have a significant influence on biodiversity.

Distribution of species

“Historically studies looking at the distribution of species across Earth’s latitudinal gradient have overlooked the role of trophic ecology – how what animals eat impacts where they are found,” explained study co-author Trisha Atwood from the Department of Watershed Sciences and the Ecology Center. 

“This new work shows that predators, omnivores and herbivores are not randomly scattered across the globe. There are patterns to where we find these groups of animals.”

Pivotal factors 

Taking a closer look at these animal diversity patterns, it is obvious that regions like parts of Africa, Europe, and Greenland are unexpectedly packed with carnivores. 

Herbivores seem to favor cooler climes, while warm regions witness a dominance of omnivores. Two pivotal factors play a role in this distribution: precipitation and the rate of plant growth.

Precipitation patterns

Precipitation patterns across time play a big role in determining where different groups of mammals thrive, said Atwood. Geographical areas where precipitation varies by season, without being too extreme, had the highest levels of mammal diversity.

“Keep in mind that we aren’t talking about the total amount of rain,” noted study lead author Jaron Adkins. 

“If you imagine ecosystems around the world on a scale of precipitation and season, certain places in Utah and the Amazon rainforest fall on one end with low variability – they have steady levels of precipitation throughout the year.”

“Other regions, like southern California, have really high variability, getting about 75 percent of the annual precipitation between December and March.”

Gross primary productivity 

The second pivotal factor, the “gross primary productivity,” essentially gauges the volume of plant growth in a particular region. 

While one would expect plant growth to predominantly affect herbivores, the research unveiled a stronger connection between carnivores and plant growth.

“It was surprising that this factor was more important for predators than omnivores and herbivores,” Atwood said. “Why this is remains a mystery.”

Prevailing climate conditions

The research suggests that while evolutionary processes spur variances in species, prevailing climate conditions can tweak rates of evolutionary shifts, extinction, and animal dispersal, thus influencing both species and trait-based richness.

These insights are especially important in an era where animal diversity is plummeting due to habitat degradation and climate disruptions.

“Animal diversity can act as an alarm system for the stability of ecosystems,” Atwood said. “Identifying the ecological mechanisms that help drive richness patterns provides insight for better managing and predicting how diversity could change under future climates.”

The study is published in the journal Ecology Letters.

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