No abstract

The survival of a bird's egg depends upon its ability to stay within strict thermal limits.Avian eggshell colours have long been considered a phenotype that can help them stay within these thermal limits 1,2 , with dark eggs absorbing heat more rapidly than bright eggs.Although disputed 3,4 , evidence suggests that darker eggs do increase in temperature more rapidly than lighter eggs, explaining why dark eggs are often considered as a cost to tradeoff against crypsis [5][6][7] . Although studies have considered whether eggshell colours can confer an adaptive benefit 4,6 , no study has demonstrated evidence that eggshell colours have actually adapted for this function. This would require data spanning a wide phylogenetic diversity of birds and a global spatial scale. Here we show evidence that darker and browner eggs have indeed evolved in cold climes, and that the thermoregulatory advantage for avian eggs is a stronger selective pressure in cold climates. Temperature alone predicted more than 80% of the global variation in eggshell colour and luminance. These patterns were directly related to avian nesting strategy, such that all relationships were stronger when eggs were exposed to incident solar radiation. Our data provide strong evidence that sunlight and nesting strategies are important selection pressures driving egg pigment evolution through their role in thermoregulation. Moreover, our study advances understanding of how traits have adapted to local temperatures, which is essential if we are to understand how organisms will be impacted by global climate change.The impact of global climate patterns on the evolution and distribution of traits is an area of increasing importance as global temperatures continue to rise. Birds' eggs are an ideal system for certified by peer review) is the author/funder. All rights reserved. No reuse allowed without permission.

No abstract

No abstract

While many studies define and measure the geographic accessibility of facilities, research has failed to explain why the accessibility is high or low, except to conjecture that it has to do with (1) the number of facilities or (2) the locations of these facilities. We demonstrate that accessibility may also be low in a region because (3) the transportation network is inefficient or (4) the population distribution is difficult to serve with few facilities. This paper also develops measures for the degree each of these four factors affect accessibility using p-median and GIS techniques. An example is provided using hospital locations in four southern US states. JEL Classification