Abstract
The altitudinal gradient in diversity of dung beetles (Scarabaeidae) was studied in a Mediterranean mountain chain located in Central Anatolia to (i) determine if there are altitudinal differences between the main taxonomic groups, (ii) describe the seasonal variations in these assemblages and (iii) assess whether closed habitats influence dung beetle diversity differentially at different altitudes. Beetles were collected throughout a year at 14 localities between 469 and 1810 m above sea level in three different types of habitats. Dung beetle assemblages at 400 to 1200 m did not vary greatly in species richness, abundance and biomass. However, they varied in composition, with the assemblages dominated by species of Scarabaeinae up to 900 m, whereas in the mid-mountain assemblages (from 900 m to 1600 m) the numbers of species of Aphodiinae was higher. The decline with increase in altitude in richness, abundance and biomass of both small and large species of Scarabaeinae up to 1500 m, together with the constancy of these parameters in the case of Aphodiinae, accounts for the changes in the composition from the lowland to mid-mountain localities. Unlike at other Mediterranean localities, the open/closed structure of the habitat only slightly influences these assemblages independently of altitude or season. The general seasonal pattern follows the classical Mediterranean bimodal pattern associated with summer drought, but the patterns are more complex when the seasonal responses of the different groups and at different localities are analysed separately. We propose that the interplay between local climatic conditions (mainly temperature) and evolutionary conserved species preferences accounts for both the current seasonal and altitudinal gradients and the changes in species composition in terms of Aphodiinae and Scarabaeinae.
Highlights
Altitudinal gradients in diversity and composition of ectothermic animals, such as insects, have been studied in different regions of the world (e.g., McCoy, 1990; Szewczyk & McCain, 2016; Beck et al, 2017; Laiolo et al, 2018)
The results clearly show that an increase in altitude is associated with a decrease in species richness, abundance and biomass of assemblages of dung beetles with no evidence of a mid-altitudinal peak
The altitudinal gradient in dung beetles at the eastern Euro-Mediterranean locality studied appears to be mid-way between what is recorded in south-western Mediterranean mountain ranges and in northernmost mountain chains at the boundary of the Pleistocene glaciated territory
Summary
Altitudinal gradients in diversity and composition of ectothermic animals, such as insects, have been studied in different regions of the world (e.g., McCoy, 1990; Szewczyk & McCain, 2016; Beck et al, 2017; Laiolo et al, 2018). The main factors associated with altitudinal gradients in diversity are related to the following: (i) the biological effects of the decrease in temperature, energy or productivity with altitude (Brown et al, 2004); (ii) the role played by geometric or spatial constraints, such as the mid-domain effect (Colwell & Lees, 2000) or the decrease in area with altitude (Rosenzweig, 1995); (iii) the generally disturbed status of lowlands landscapes (McCoy, 1990); (iv) the juxtaposition of species groups with different climatic tolerances (Lomolino, 2001; Oommen & Shanker, 2005); or even (v) the role played by contingent factors related to the idiosyncratic evolution of the involved groups and the composition of the regional pool of species (Ricklefts, 2006; Laiolo et al, 2018).
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