Ogutu: warming is a threat to biodiversity
Warmer temperatures and drier weather conditions have significantly affected the composition of wildlife in Kenya’s Lake Nakuru National Park, situated in the heart of the Rift Valley, states a new study published on January 28, 2012. The Nakuru region has experienced perhaps one of the fastest warming rates in the region in the past half a century.
This, associated with human encroachment around Kenya’s first fully fenced-protected park, has seen the numbers of two wildlife species plummet to levels that now threaten their future population viability in the park although, surprisingly, the park continues to hold a high level of biodiversity including the world famous flamingos.
The trends of nine (9) most common herbivore species were studied in the 41 years from 1970 to 2011. The study found that the waterbuck, once a flagship species whose population density in the park was the highest known anywhere until the mid 1990s, has lost its position of dominance to buffalo and zebra, while Grant’s gazelle and impala at first increased and then gradually declined. Both the waterbuck and warthog decreased in numbers to levels that now threaten their very survival in the park while the buffalo, zebra and Thomson’s gazelle continued to thrive. Populations of the other three common species were relatively stable.
The crash of the waterbuck population following the 1990 drought is attributed to competition for forage between waterbuck, on the one hand, and buffalo and zebra, on the other. There are extensive overlaps in the forage consumed by the three species but waterbuck select a diet far richer in crude protein and thus requires plenty of water to excrete the nitrogenous waste in urine. It therefore has a much higher minimum requirement of water than most African ungulates.
Waterbuck crashes, duickers disappear
Consequently, as more animals seek to feed around the lake shore during dry periods, the forage gets depleted faster and selective feeders like the waterbuck suffer the most. Thomson’s gazelle, impala and waterbuck that are the most strongly dependent on the lakeshore grasslands that become more extensively exposed under dry conditions when the lake level recedes, have to compete more intensely with the expanding buffalo and zebra populations. Zebra and buffalo have a competitive edge over these smaller grazers on the lake shore grasslands, as well as on grasslands around the artificial water points dispersed all over the park in the dry season, when food supply is lowest elsewhere. This is because both buffalo and zebra can tolerate low-quality grasses because of their bulk-feeding style due to their large body sizes and also because zebra is a non-ruminant grazer able to rapidly process large quantities of low-quality forage.
It is not only the common smaller species that are bearing the brunt of the increase in numbers of the larger species in the park. The small and rare species are facing even harder times. So for example, the mountain reedbuck that was once the fourth most abundant species in the park during 1970-1971 and the common and blue duikers have all but virtually disappeared from the park due to the loss of their favoured habitats of tall grasslands and shoreline vegetation due to grazing by the expanding numbers of the large-sized grazers.
The lack of a water outlet and the small size of Lake Nakuru make it very vulnerable to habitat degradation and changing land use in its 1800 Km2 catchment basin. The massive destruction of forests in the catchment basin and the alteration of the catchment hydrology have destroyed most of the wildlife that previously existed in the region; described by early European explorers as the richest found anywhere in East Africa. As a result of these changes, populations of elephant, Jackson’s hartebeest, Masai and Rothschild giraffes, white rhinoceros, and eland became locally extinct. A once spectacular migration of zebra and Thomson’s gazelles between Lake Baringo and the Lake Nakuru-Elementaita region also disappeared.
The waterbuck: Its survival in Lake Nakuru threatened
Being located right next to Nakuru town, the park is gradually being adversely affected by water pollution due to industrialisation and the lake level has dropped from 2.5 m (in 1925-1979) to 1.01 m during 1992-2002 and now stands at 0.756 m (2003 to 2011), reflecting high siltation rates.
Water quality in the streams supplying water to the lake is also deteriorating exposing animals to potentially dangerous agro chemicals and heavy metals.
It is indeed very striking that this small park has been able to support such large numbers of a diverse large mammal assemblage for over four decades, despite wide climatic variation and major land use changes in its surroundings. However, although the long-term consequences of the population expansion and increasing isolation of the park are uncertain at present, when the expanding populations reach their carrying capacity in the park, they may become more vulnerable to rainfall, temperature and lake level influences on their food resources and large predators, with ramifying and unforeseen adverse consequences for the other species.
The study titled Dynamics of ungulates in relation to climatic and land use changes in an insularized African savannah ecosystem, was published in Biodiversity and Conservation journal by Joseph Ogutu, a senior statistician in the Bioinformatics unit of the University of Hohenheim, Germany. He conducted the study with colleagues there and at the International Livestock Research Institute in Nairobi, Kenya, where he initially served under the People, Livestock and Environment theme.
Masai Mara National Reserve
Ogutu previously published extensive studies on the world famous Masai Mara National Reserve (2011 and 2009). The 2011 study published in the Journal of Zoology indicated that the populations of wildlife species in the world-renowned Masai Mara reserve in Kenya have crashed in the past three decades by as much as 70%.
Fewer survive beyond the reserve in the wider Mara, where buffalo and wild dogs have all but disappeared, while huge numbers of wildebeest no longer pass through the region on their epic migration.
However, numbers of cattle grazing in the reserve have increased by more than 1100% per cent, although it is illegal for them to so do. This explosion in the numbers of domestic livestock grazing in the Mara region, including within the Masai Mara national reserve, is one of the principal reasons wildlife has disappeared, the scientists said.
‘The status of Masai Mara as a prime conservation area and premier tourist draw card in Kenya may soon be in jeopardy’ Ogutu’, said at the time.
By Jane Gitau
Peter Thorne has joined ILRI as a crop livestock systems scientist. He is part of the People Livestock and Environment theme based in Addis Ababa and is expected to relocate to Zimbabwe in mid-2012.
The first report from the ‘livestock intensification project on dairy value chains in India and Ethiopia’ (funded by the OPEC Fund for International Development) has just been released.
