Biodiversity patterns diverge along geographic temperature gradients.

Area of Science:

• Ecology
• Biodiversity Science
• Climate Change Biology

Background:

• Space-for-time substitution models projecting ecological responses to climate change often assume elevational and latitudinal equivalence.
• Mismatches between elevational and latitudinal gradients can affect the capacity of habitats to serve as climatic refuges for dispersing species.
• Zooplankton, crucial aquatic food web components, are ectothermic and sensitive to temperature, making them ideal indicators of climate change impacts.

Purpose of the Study:

• To test the assumption of elevational and latitudinal equivalence in ecological models.
• To assess zooplankton biodiversity patterns across steep elevation and latitude gradients in western North America.
• To determine how temperature influences biodiversity and community assembly along these gradients.

Main Methods:

• Compiled zooplankton community data from over 1200 mountain lakes and ponds.
• Analyzed species richness, phylogenetic diversity, and functional diversity across gradients of ~3750 m elevation and 30° latitude.
• Investigated the relationship between temperature (mean annual and seasonal) and biodiversity patterns.

Main Results:

• Species richness, phylogenetic, and functional diversity showed contrasting responses across elevational and latitudinal gradients.
• Diversity metrics plateaued at low elevations but peaked at intermediate latitudes.
• Non-monotonic (hump-shaped) diversity trends with latitude were influenced by geographic interactions, with weaker latitudinal relationships at higher elevations.
• Mean annual temperature predicted elevational richness but not latitudinal trends, indicating differing drivers of community assembly.

Conclusions:

• Elevational and latitudinal gradients exhibit contrasting biodiversity responses, challenging the assumption of equivalence in ecological models.
• Shifting environmental filters and limiting similarity influence community assembly differently with increasing elevation and latitude.
• Warming impacts on biodiversity differ between gradients, suggesting varied limits on climatic refugia and potential barriers to northward range expansion for aquatic species.