Biodiversity patterns diverge along geographic temperature gradients

Models applying space-for-time substitution, including those projecting ecological responses to climate change, generally assume an elevational and latitudinal equivalence that is rarely tested. However, a mismatch may lead to different capacities for providing climatic refuge to dispersing species. We compiled community data on zooplankton, ectothermic animals that form the consumer basis of most aquatic food webs, from over 1200 mountain lakes and ponds across western North America to assess biodiversity along geographic temperature gradients spanning nearly 3750 m elevation and 30° latitude. Species richness, phylogenetic relationships, and functional diversity all showed contrasting responses across gradients, with richness metrics plateauing at low elevations but exhibiting intermediate latitudinal maxima. The nonmonotonic/hump-shaped diversity trends with latitude emerged from geographic interactions, including weaker latitudinal relationships at higher elevations (i.e. in alpine lakes) linked to different underlying drivers. Here, divergent patterns of phylogenetic and functional trait dispersion indicate shifting roles of environmental filters and limiting similarity in the assembly of communities with increasing elevation and latitude. We further tested whether gradients showed common responses to warmer temperatures and found that mean annual (but not seasonal) temperatures predicted elevational richness patterns but failed to capture consistent trends with latitude, meaning that predictions of how climate change will influence diversity also differ between gradients. Contrasting responses to elevation- and latitude-driven warming suggest different limits on climatic refugia and likely greater barriers to northward range expansion.

Distributional Patterns of Aquatic Empididae (Diptera) along an Elevational Diversity Gradient in a Low Mountain Range: An Example from Central Europe

Simple Summary

The insect distribution and diversity depend on many different abiotic and biotic factors, which is especially well documented in the high mountains but has not been studied in detail in the low mountain massifs. We studied 17 different macro and microhabitat factors that influence the altitudinal distribution of 40 Hemerodromiinae and Clinocerinae species in the Pieniny Mts., Poland. This is the first such study in Central Europe and one of only a few in the world. The results clearly show that species richness and distribution of Hemerodromiinae and Clinocerinae species are changing with the elevational gradient, with a monotonic decline in species richness with increasing elevation observed for the first subfamily and the hump-shaped distribution pattern noted for the second subfamily, as well as the size of the stream/river and the surrounding area in species distribution in the Pieniny Mts.

Abstract

The two subfamilies Hemerodromiinae and Clinocerinae, also known as aquatic dance flies, are a group of small predatory insects occurring mainly in mountainous areas and the northern temperate. However, very little is known about distribution patterns for most of the species. Habitat preferences for 40 aquatic empidid species were analysed in the Pieniny Mts., Poland. Forty-six sampling sites from a major part of this relatively low mountain massif (400–770 m) were chosen, for which 17 micro and macrohabitat environmental variables were measured including both abiotic (altitude, stream mean width and depth, and shading) and biotic factors (13 dominant plant communities). Here we show that numerous studied aquatic Empididae were characterized by unique habitat preferences and were restricted to the foothills or the lower montane zone with only a few species characterized by wider elevational distribution. Chelifera pectinicauda, C. flavella, C. subangusta and Phyllodromia melanocephala (Hemerodromiinae), and Clinocera appendiculata, C. fontinalis, C. wesmaeli, Dolichocephala guttata, D. oblongoguttata, Kowarzia plectrum, Wiedemannia jazdzewskii, and W. thienemanni (Clinocerinae) were clearly associated with the highest altitudes and shaded areas while W. bistigma, W. lamellata, W. phantasma, and W. tricuspidata (Clinocerinae) were clearly associated with the lower elevated, wider stream valleys overgrown by willow brakes. Species richness and diversity decreased along elevational gradient with the hump-shaped diversity pattern noted for the subfamily Clinocerinae. The altitude, size of river/stream as well as the type of plant community were found as the most important factors in the distribution of the studied aquatic empidid species. The present study is the first one focused on elevational diversity gradient and habitat preferences of Hemerodromiinae and Clinocerinae of central Europe, and one of only a few in the world.