Research Highlights (2008, 2007)



Topic: explanations for bird species range size in an island scenario

* Understanding why species are more or less broadly distributed within their geographical limits is one of the cornerstones of macroecology and biogeographical ecology, with important implications for biological conservation. Here we explore the determinants of island occupancy of terrestrial bird species in an oceanic archipelago, accounting for ecological components while controlling for phylogenetic effects.

* Island occupancy of 48 bird species had a very low phylogenetic effect. Species with broader habitat breadth, stronger preferences for urban environments, smaller body size, and a lower degree of endemicity had a broader geographical distribution in the archipelago. The positive relationship of range size with local abundance, previously shown in continental studies, was not found, probably because it relies on free dispersal on continuous landmasses, which may not be applicable on oceanic islands. Read more [… y más]


Topic: population trends of Spanish birds are related to habitat and climatic preferences

* Both long- and short-term changes in population numbers are being used to define the international conservation status of species. Nevertheless, little is known about the association between some basic biological features of species and their population trends. Working with common passerines of the Spanish avifauna, we investigate (1) whether there are characteristics shared among species with upwards or downwards trends, and (2) whether population changes agree with what could be expected under global warming (a decrease in species typical of cooler environments).

* One-half of these species have shown a generalized pattern towards the increase of their populations, while only one-tenth showed a significant decrease. Species showing more marked increases preferred wooded habitats, were habitat generalists and occupied warmer and wetter areas, while moderate decreases were found for open country habitats in drier areas. These results disagree with the proposed detrimental effect of global warming on bird populations of western Europe, and suggest that factors other than the increase in temperature may be brought to discussions on global change as relevant components to explain recent changes in avian biodiversity. Read more.


Topic: climate change and outbreaks of amphibian chytridiomycosis in a montane area of Central Spain

* Amphibian species are declining at an alarming rate on a global scale in large part owing to an infectious disease caused by the chytridiomycete fungus, Batrachochytrium dendrobatidis. Here, we use long-term observations on amphibian population dynamics in the Pen˜ alara Natural Park, Spain, to investigate the link between climate change and chytridiomycosis.

* Our analysis shows a significant association between change in local climatic variables and the occurrence of chytridiomycosis within this region. Specifically, we show that rising temperature is linked to the occurrence of chytrid-related disease, consistent with the chytrid-thermal-optimum hypothesis. Read more.


Topic: threshold distances to nearby cities and roads influence the avifauna in a mosaic landscape

* Urban developments and road networks extend their impacts on the surrounding habitats along a variable distance, affecting birds living in natural environments. This study identifies the threshold distances upon which several cities and roads alter the abundance patterns of the native avifauna across a large mosaic landscape in Central Spain.

* Nearby cities did not affect the total bird species richness in natural habitats of the study region. Total bird abundance increased near urban areas, mainly through its positive influence on urban-exploiter species. The effect of roads was negative and highly generalized, although threshold distances to roads vary among different groups of species. The bird communities of deciduous woodlands showed higher resilience to deletereous influences from nearby cities and roads. Buffer distances determining most significant impacts were 400m for urban areas, and 300m for roads. Read more.


Topic: effects of latitude and day length on fattening strategies of a small bird during winter

* Cyclic daily fattening routines are very common in wintering small wild birds, and are thought to be the consequence of a trade-off between different environmental and state-dependent factors, such as starvation risk and mass-dependent predation costs. We examine if geographically separate populations of coal tits, wintering in Scotland and central Spain under contrasting photoperiods, show differences in their strategies of daily mass regulation. We describe population differences in wild birds under natural conditions, and experimentally search for interpopulation variation in diurnal body mass increase under common, manipulated, photoperiod conditions, controlling for temperature, food availability, predator pressure and foraging arena.

* Fattening patterns are plastic, with birds responding directly to the photoperiod that they experience, suggesting that they are continually making finescale adjustments to energy reserves on the basis of both inherent (e.g. state-dependent) and extrinsic cues. Under controlled photoperiod situations, the pattern of daily mass gain was similar in both populations: diurnal body mass gain was more accelerated at the end of the day, and the increase in body mass in the first hour of the day was considerably lower under the long (9 h) than under the short (7 h) photoperiod in both populations. However, birds in the wild at lower latitudes (with longer winter days) had a greater tendency to delay mass gain until late in the day. Read more.