Competitive exclusion along climate gradients: energy efficiency influences the distribution of two salmonid fishes

We tested the importance of thermal adaptations and energy efficiency in relation to the geographical distribution of two competing freshwater salmonid fish species. Presence–absence data for Arctic char and brown trout were obtained from 1502 Norwegian lakes embracing both temperature and productivity gradients. The distributions were contrasted with laboratory‐derived temperature scaling models for food consumption, growth and energy efficiency. Thermal performances of the two species were almost identical. However, Arctic char exhibited double the growth efficiency (per unit of food) and appear to have out‐competed brown trout from cold, low‐productivity lakes, perhaps by scramble competition. Brown trout, for which previous reports have shown to be aggressive and dominant, have likely excluded the more energy‐efficient Arctic char from relatively warm, productive lakes, perhaps by contest competition. Competitive interaction changing in outcome with lake productivity, rather than thermal performance, is likely a major determinant of the range distribution of the two species. Our study highlights the need for more focus on choice of relevant ecophysiological traits in ecological climate impact studies and species distribution modelling.     

A revision of Afrotropical Agabus Leach (Coleoptera, Dytiscidae), and the evolution of tropicoalpine super specialists

Abstract. The thirteen species of Agabus Leach, 1817, of the Afrotropical Region are revised and classified into four species groups: the dibasic ambulator -group endemic to Ethiopia, ragazzii -group with five species in Ethiopia, raffrayi -group with five species in East and South Africa, and A.discicollis Ancey, 1882, endemic to Ethiopia, is placed in the Nearctic cordatus -group. Agabus perssoni sp.n. and Agabus galamensis sp.n. are described from the highlands of Ethiopia. Agabus ruwenzoricus Guignot, 1936, stat.n. is given specific rank. Agabus ferrugatus Régimbart, 1905, is synonymized with Agabus ragazzii Régimbart, 1887, and Agabus limbicollis Régimbart, 1905, is synonymized with Agabus raffrayi Sharp, 1882, syn.n. Lectotypes are designated for the following nominal species: Agabus discicollis Ancey, 1882, Agabus raffrayi Sharp, 1882, Agabus limbicollis Régimbart, 1905, Agabus pallidus Omer-Cooper, 1931, Agabus ruwenzoricus Guignot, 1936, Agabus sjostedti Régimbart, 1908, Agabus dytiscoides Régimbart, 1908, Agabus ragazzii Régimbart, 1887, Agabus ferrugatus Régimbart, 1905, and Gaurodytes abessinicus Zimmermann, 1928. Reconstructed phylogenies are presented for the raffrayi -and ragazzii -groups. The following adaptations to tropicoalpine habitats are suggested: (1) body and especially pronotum narrow, (2) head broad anteriorly, (3) hindwing small, and (4) hind leg long and slender. Biogeography and evolution of the studied species are discussed. Four different invasions of Holarctic lineages to the East African mountains are suggested. Recurrent periods of cold and dry climate are considered the chief driving force in the evolution of high altitude super specialists.