The emergence and abundance of cooperation in nature poses a tenacious and challenging puzzle to evolutionary biology. Cooperative behaviour seems to contradict Darwinian evolution because altruistic individuals increase the fitness of other members of the population at a cost to themselves. Thus, in the absence of supporting mechanisms, cooperation should decrease and vanish, as predicted by c...

Group size is an important variable describing behavioural ecology of animals. A variety of factors such as habitat characteristics, life history, spatio-temporal resource dynamics, population density, predation risk, competition with kin, and social learning often determine group size in large mammals. We studied temporal dynamics of group size in Siberian Ibex (Capra sibirica) in a protected ...

two iranian strains of brachionus rotifers were cultured under different food and salinity regimes. the rotiferswere fed with five algal types (freshwater and marine chlorella vulgaris, nannochloropsis occulata, isochrysisgalbana and scenedesmus obliquus) at three different salinities (5, 15 and 25 g/l) and their reproductive and growth parameters were assessed. the maximum number of ovigerous ...

the diamondback moth, plutella xylostella (linnaeus, 1758) (lep.: plutellidae) is the most destructive insect pest of crucifer plants throughout the world. in order to study its seasonal population fluctuation, sampling was conducted in the cauliflower fields of south of tehran from late may until october 2011. one hectare cauliflower field in the middle of a large field was randomly selected i...

This paper shows, in a two-sector Malthusian model of endogenous population growth, that output per capita, population density, and industrialization depend upon the labor intensity of agricultural production. Because the diminishing returns to labor are less pronounced, high labor intensity (as in rice production) leads not only to a larger population density but also to lower output per capit...

Individual learning and social learning are two primary abilities supporting cultural evolution. Conditions for their evolution have mostly been studied by investigating gene frequency dynamics, which essentially implies constant population size. Predictions from such "static" models may only be of partial relevance to the evolution of advanced individual learning in modern humans, because mode...

BACKGROUND Between 1955 and 2011 there were marked fluctuations in suicide rates in Sri Lanka; incidence increased six-fold between 1955 and the 1980s, and halved in the early 21st century. Changes in access to highly toxic pesticides are thought to have influenced this pattern. This study investigates variation in suicide rates across Sri Lanka's 25 districts between 1955 and 2011. We hypothes...