Abstract
Over the past half-century, large mammal populations have declined substantially throughout East Africa, mainly due to habitat loss and unsustainable direct exploitation. While it has been acknowledged that the loss of large mammals can have direct and cascading effects on community composition and ecosystem characteristics, limited quantitative work has been done on how declines of large herbivore populations impacts the abundance of mutualistic symbionts. Using a space-for-time observational approach, we quantified the large mammal community alongside the densities, host preferences and behaviors of mutualistic red-billed oxpeckers (Buphagus erythrorhynchus), and yellow-billed oxpeckers (Buphagus africanus) in northern Tanzania. At the landscape scale, mammal community composition was substantially less diverse in highly human-dominated areas when compared with more protected areas, with an observed complete loss of large wild mammal species in two study areas. Mirroring this trend, oxpecker densities were lowest in the least protected areas, and highest in fully protected areas. Using resource selection functions implemented via generalized linear models at different scales, we found that oxpeckers (1) were predominantly (67% of red-billed oxpeckers; 70% of yellow-billed oxpeckers) feeding on larger (between 500kg and 1500kg) ungulate host species within the mammal community, (2) usually preferred feeding on larger individuals (adults and males) within a specific host species population, and (3) preferred hosts that were more tolerant of their presence. In particular, cattle were especially intolerant of oxpecker presence and were relatively effective in displacing oxpeckers. We found little evidence that oxpecker feeding was parasitic across all host species; wound feeding was only observed on giraffe, comprising 6% and 4% of feeding behavior in red-billed and yellow-billed oxpeckers respectively. Thus, a loss of large-bodied and oxpecker tolerant host species is a likely explanation for declines of oxpecker populations in human dominated landscapes, which may have further cascading effects.
Highlights
The decline and/or loss of large mammals can have cascading effects on ecosystems, which can prompt ecological, economic, and socio-cultural consequences [1,2,3]
This study was conducted in six distinct units of the Tarangire-Manyara Ecosystem (TME): Karatu District (KD), Mto wa Mbu Game Controlled Area (GCA), Manyara Ranch (MR), Burunge Wildlife Management Area (BWMA), Tarangire National Park (TNP), and Lake Manyara National Park (LMNP; Fig 1)
RBO density was lowest in KD and GCA, intermediate in MR, BWMA, and TNP, and highest in LMNP (Fig 2)
Summary
The decline and/or loss of large mammals can have cascading effects on ecosystems, which can prompt ecological, economic, and socio-cultural consequences [1,2,3]. Whereas wildlife declines have substantial and obvious economic and socio-cultural effects such as lower animal protein supply to local populations [5] and the decline of regional tourism [6], indirect ecological effects can be difficult to predict due to complex interspecific interactions and often-unexpected feedback loops between animals and their environment [1, 2, 7]. Losses of large mammal populations can have cascading effects on vegetation structure within a habitat through direct utilization [8] and seed dispersal [9, 10], the direction and strength of these interactions can be variable [1]. Examples of contemporary coextinctions are sparse, and coextinction predictions are often made utilizing incomplete information about an associated species’ life history and host specificity [12]
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