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Tuesday, 7 October 2014

Ecology and Evolution: October 2014. New articles: Bar-tailed Godwit distribution; island bird population variation.

Ecology and Evolution

Cover image for Vol. 4 Issue 19

October 2014 - Open Access Articles

Determinants of bird species richness, endemism, and island network roles in Wallacea and the West Indies: is geography sufficient or does current and historical climate matter?

Bo Dalsgaard, Daniel W. Carstensen, Jon Fjeldså, Pietro K. Maruyama, Carsten Rahbek, Brody Sandel, Jesper Sonne, Jens-Christian Svenning, Zhiheng Wang and William J. Sutherland

Article first published: 2 OCT 2014 | DOI: 10.1002/ece3.1276

LINK    pdf

Abstract
Island biogeography has greatly contributed to our understanding of the processes determining species' distributions. Previous research has focused on the effects of island geography (i.e., island area, elevation, and isolation) and current climate as drivers of island species richness and endemism. Here, we evaluate the potential additional effects of historical climate on breeding land bird richness and endemism in Wallacea and the West Indies. Furthermore, on the basis of species distributions, we identify island biogeographical network roles and examine their association with geography, current and historical climate, and bird richness/endemism. We found that island geography, especially island area but also isolation and elevation, largely explained the variation in island species richness and endemism. Current and historical climate only added marginally to our understanding of the distribution of species on islands, and this was idiosyncratic to each archipelago. In the West Indies, endemic richness was slightly reduced on islands with historically unstable climates; weak support for the opposite was found in Wallacea. In both archipelagos, large islands with many endemics and situated far from other large islands had high importance for the linkage within modules, indicating that these islands potentially act as speciation pumps and source islands for surrounding smaller islands within the module and, thus, define the biogeographical modules. Large islands situated far from the mainland and/or with a high number of nonendemics acted as links between modules. Additionally, in Wallacea, but not in the West Indies, climatically unstable islands tended to interlink biogeographical modules. The weak and idiosyncratic effect of historical climate on island richness, endemism, and network roles indicates that historical climate had little effects on extinction-immigration dynamics. This is in contrast to the strong effect of historical climate observed on the mainland, possibly because surrounding oceans buffer against strong climate oscillations and because geography is a strong determinant of island richness, endemism and network roles.

Keywords:
Birds;Caribbean;current climate;endemism;historical climate;island biogeography;modularity;species richness;Wallacea;West Indies

Figure 1
Four bird species representing a nonendemic and an endemic species to Wallacea (left) and the West Indies (right). Upper left: Olive-flanked Whistler (Hylocitrea bonensis) endemic to Sulawesi, the largest island in Wallacea. Lower left: Brown-throated Sunbird (Anthreptes malacensis), a nonendemic species found on Sulawesi and other islands in the western part of Wallacea and throughout much of South-East Asia. Upper right: Yellow-faced Grassquit (Tiaris olivacea) is a nonendemic West Indian species mainly found on large Greater Antillean islands, or nearby satellite islands, and in Central America and the northwestern South America. Lower right: Narrow-billed Tody (Todus angustirostris) is endemic to Hispaniola, the second largest and the most mountainous islands of the West Indies. Illustrations by Jon Fjeldså.















Sex-specific winter distribution in a sexually dimorphic shorebird is explained by resource partitioning.

Sjoerd Duijns, Jan A. van Gils, Bernard Spaans, Job ten Horn, Maarten Brugge and Theunis Piersma


Article first published: 2 OCT 2014 | DOI: 10.1002/ece3.1213

LINK    pdf

Abstract
Sexual size dimorphism (SSD) implies correlated differences in energetic requirements and feeding opportunities, such that sexes will face different trade-offs in habitat selection. In seasonal migrants, this could result in a differential spatial distribution across the wintering range. To identify the ecological causes of sexual spatial segregation, we studied a sexually dimorphic shorebird, the bar-tailed godwit Limosa lapponica, in which females have a larger body and a longer bill than males. With respect to the trade-offs that these migratory shorebirds experience in their choice of wintering area, northern and colder wintering sites have the benefit of being closer to the Arctic breeding grounds. According to Bergmann's rule, the larger females should incur lower energetic costs per unit of body mass over males, helping them to winter in the cold. However, as the sexes have rather different bill lengths, differences in sex-specific wintering sites could also be due to the vertical distribution of their buried prey, that is, resource partitioning. Here, in a comparison between six main intertidal wintering areas across the entire winter range of the lapponica subspecies in northwest Europe, we show that the percentage of females between sites was not correlated with the cost of wintering, but was positively correlated with the biomass in the bottom layer and negatively with the biomass in the top layer. We conclude that resource partitioning, rather than relative expenditure advantages, best explains the differential spatial distribution of male and female bar-tailed godwits across northwest Europe.

Keywords:

Bergmann's rule;habitat selection;intertidal ecology; Limosa lapponica ;prey accessibility;sexual size dimorphism (SSD)

Figure 1
Map of North-western Europe, encompassing all wintering sites of bar-tailed godwits. Location of the study sites, with the mean January numbers of bar-tailed godwits (1995–2005) counted at high-tide roosts, based on the Wetlands International midwinter count database. Mean winter temperature data (1950–2000), of high spatial resolution, were derived from satellite images through interpolation of climate data (Hijmans et al. 2005). There is a clear gradient in temperature from Sylt-Rømø Wadden Sea to the Dutch Western Wadden Sea, to the UK and Ireland and southern wintering areas in France.




















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