Savannahs make up about 20% of the world’s land surface, whereas African savannahs constitute 50%
of the land area and have been used as parks to conserve nature and for outdoor recreation. However,
conserving biodiversity in these ecosystems has been challenging due to increasing pressures,
potential loss of habitat and species or lack of up-to-date data in some of the protected areas. In this
thesis, I investigated the state of biodiversity in Akagera National Park (ANP), Rwanda, and factors
affecting its distribution. The work of this thesis is based on the results of large-scale, replicated point
counts and presence-absence surveys conducted between August 2009 and August 2011 in the
savannah habitats of the park. ANP plays an important role in conserving about 525 bird species
known from the park and > 50 species of large mammals. Systematic plots of equally-spaced 1-km2
(n
= 266) were used for both bird and large mammal censuses. The Chao2 estimator and the Simpson
index were used to estimate and compare bird species richness and diversity, respectively, between
inside and outside the park. Generalized linear models (GLMs) were used to investigate relationships
between bird diversity and habitat structure, whereas Distance sampling methods were used for
estimating both population sizes and densities of large mammals.
Despite recent important changes in habitats and fauna of the ANP, the results of this
thesis show that the park has maintained an important diversity of birds. The 301 bird species recorded
during my study represents 43% of Rwanda’s checklist of birds (i.e. 697 species), underlining that
ANP still contributes to the conservation of birds (Paper I). The results highlight that ANP still
maintained special and important ornithological features, including the presence of endemic species of
the Lake Victoria region, globally threatened species, those that have not previously been recorded in
Akagera and a large number of Palearctic and Afrotropical migrants (Paper I). The abundance of bird
species was found to be linked to human influence (Paper II). In fact, this thesis found large human
effects on both the grassland habitat (e.g. reduction of grass biomass and the presence of tall grass by
57% and 76%, respectively) and bird species richness which significantly varied between inside and
outside the park due to different land use practices between the two types of habitat. However, human
activities did not affect species diversity.
This thesis further revealed significant relationships between habitat structure and bird
species richness that varied between inside and outside the park (Paper III). However, habitat structure
did not correlate with species diversity. Paper III also demonstrated that single savannah species use
habitats differently due to individual niche characteristics and niche interactions with other species.
Estimates of the total population and density of large mammals varied for each species and the most
abundant large herbivores were impalas, buffaloes, topis, baboons and zebras (Paper IV). High
population sizes and densities of Ankolé found both inside and outside the park might have an impact
on wildlife. Similarly, large population sizes of large mammals that are still outside the park pose a
conservation challenge. Compared to previous surveys of the park (e.g. 1990, 1997/1998, 2002 &
2010), the findings of this thesis demonstrate that most large wild herbivores declined between 1990
and 2011 except zebras, warthogs and duikers that rather increased. Habitat structure was also found to
affect the distribution and abundance of large mammals. Finally, I hope that my results provide new
inputs for further strengthening of efforts to conserve the park’s biodiversity and might be useful for
further assessment of the relationships between species diversity/richness and community stability as
well as ecosystem function.