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

Iwona Słowińska,Radomir Jaskuła

doi:10.3390/insects12020165

Abstract

Simple SummaryThe 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.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.

Highlights

One of the most universal biogeographical patterns of species richness, known as the latitudinal gradient in species diversity, shows the decline of species richness from the tropics towards the Poles
Very little is known about Diptera distributional patterns in lower mountain ranges [49], which is sometimes explained by the absence of significant climatic factors differentiating fauna in such mountain massifs including a lack of strict altitudinal zonation
Almost 60% of all aquatic empidids collected in the study were caught in the Dunajec, the major river in the Pieniny Mts., with Wiedemannia bistigma as the most abundant species recorded at all sampling sites along this river (19,038 individuals or 46.3% of clinocerines)

Summary

Introduction

One of the most universal biogeographical patterns of species richness, known as the latitudinal gradient in species diversity, shows the decline of species richness from the tropics towards the Poles. Many ecological studies reveal two main patterns of relationships between species richness and altitude: a monotonic decline in species richness with increasing elevation, and a hump-shaped relationship, with mid-elevation peaks in species richness [1]. Both models are well documented by studies focused on plants and vertebrates, especially birds and mammals [2,3,4,5,6,7,8,9,10]. More data are needed to confirm such hypothesis, generally it is known that the distribution of many fly species seems to be strictly connected with altitude, with some species occurring only in the higher parts of the mountains, others are known only from the lower elevations while some opportunistic taxa can be found along the entire elevational gradient

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