Revisiting biogeography of livestock animal domestication

Human society relies on four main livestock animals – sheep, goat, pig and cattle, which all were domesticated at nearly the same time and place. Many arguments have been put forward to explain why these animals, place and time were suitable for domestication, but the question – why only these, but not other animals, still does not have a clear answer. Here we offer a biogeographical perspective: we survey global occurrence of large mammalian herbivore genera around 15 000 – 5 000 years before present and compile a dataset characterising their ecology, habitats and dental traits. Using predictive modelling we extract patterns from this data to highlight ecological differences between domesticated and nondomesticated genera. The most suitable for domestication appear to be generalists adapted to persistence in marginal environments of low productivity, largely corresponding to cold semi-arid climate zones. Our biogeographic analysis shows that even though domestication rates varied across continents, potentially suitable candidate animals were rather uniformly distributed across continents. We interpret this pattern as a result of an interface between cold semi-arid and hot semi-arid climatic zones. We argue that hot Semi-arid climate was most suitable for plant domestication, cold Semi-arid climate selected for animals most suitable for domestication as livestock. We propose that the rates of domestication across biogeographic realms largely reflect how much intersection between hot and cold Semi-arid climatic zones was available at each continent.

Herbivore teeth predict climatic limits in Kenyan ecosystems

A major focus in evolutionary biology is to understand how the evolution of organisms relates to changes in their physical environment. In the terrestrial realm, the interrelationships among climate, vegetation, and herbivores lie at the heart of this question. Here we introduce and test a scoring scheme for functional traits present on the worn surfaces of large mammalian herbivore teeth to capture their relationship to environmental conditions. We modeled local precipitation, temperature, primary productivity, and vegetation index as functions of dental traits of large mammal species in 13 national parks in Kenya over the past 60 y. We found that these dental traits can accurately estimate local climate and environment, even at small spatial scales within areas of relatively uniform climate (within two ecoregions), and that they predict limiting conditions better than average conditions. These findings demonstrate that the evolution of key functional properties of organisms may be more reflective of demands during recurring adverse episodes than under average conditions or during isolated severe events.

Population trend and distribution of the Vulnerable common hippopotamus Hippopotamus amphibius in the Mara Region of Kenya

The common hippopotamus Hippopotamus amphibius can significantly influence the dynamics of ecosystems and engender serious conflicts with people but, in Kenya, one of the species strongholds, it has been little studied or monitored. We surveyed the hippopotamus population in the Masai Mara National Reserve and the adjoining pastoral ranches in 2006 using foot counts along 155.3 km of the main rivers. We counted 4,170 hippopotamuses in 171 schools. Comparisons with earlier surveys suggest that this population increased by 169.6% between 1971 and 1980 within the reserve and, although it did not increase within the reserve during 1980–2006, it increased by 359.4% outside the reserve during this period against a background of deteriorating habitat conditions. The overall density in 2006 was 26.9 hippopotamuses km-1 of river, equivalent to a biomass of 26,677 kg km-1 of river. The ratio of calves to 100 adults was 9:100 inside the reserve, 10:100 outside the reserve and 6:100 along tributaries of the Mara River, implying that the population is either increasing or that its spatial distribution is being compressed because of range contraction. The apparent increase in the hippopotamus population contrasts with marked contemporaneous declines in the populations of most other large mammalian herbivore species in the Reserve. We discuss possible reasons underlying the increase in the hippopotamus population.