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Lions influence the decline and habitat shift of hartebeest in a semiarid savanna

2017; Oxford University Press; Volume: 98; Issue: 4 Linguagem: Inglês

10.1093/jmammal/gyx040

1545-1542

Caroline C. Ng’weno, Nelly J. Maiyo, Abdullahi H. Ali, Alfred K. Kibungei, Jacob R. Goheen,

Bat Biology and Ecology Studies

Efforts to restore large carnivores often are conducted with an assumption of reciprocity, in which prey populations are expected to return to levels approximating those prior to carnivore extirpation. The extent to which this assumption is met depends on the intensity of predation, which in turn can be influenced by the magnitude of environmental change over the period of large-carnivore extirpation. Recent declines of hartebeest (Alcelaphus buselaphus) populations in Laikipia, Kenya have coincided with recolonization by large carnivores, particularly lions (Panthera leo), over the past 20 years. To understand whether and the extent to which predation by lions underlies hartebeest declines, we monitored vital rates of hartebeest that were variably exposed to or protected from lions. Lion exclusion shifted rates of population growth from negative to positive (λ = 0.89 ± 0.04 versus 1.11 ± 0.11 for control and lion exclusion zones, respectively) and, consistent with other studies on ungulate demography, adult survival was the most sensitive and elastic vital rate. Analysis of life table response experiments revealed that 32% of the variation in population growth was due to fecundity, which had the greatest proportional effects on λ. In addition, hartebeest selected open (grassland) areas more strongly where lions occurred, and avoided areas with dense tree cover. Our work provides experimental evidence to support the hypothesis that hartebeest declines have been driven primarily by lion restoration, although we cannot eliminate the possibility that predation by spotted hyenas (Crocuta crocuta) additionally suppressed populations of hartebeest. Given that tree cover has increased across Laikipia over the past 50 years, we suggest that lion-driven declines of hartebeest have been exacerbated by landscape change. Jitihada za kuwarejesha wanyama wakubwa walao nyama inaambatana na dhana ya usawa ambapo viwango vya walao majani wanatarajiwa kurudi kama ilivyokuwa kabla ya kudhoofishwa kwa idadi ya wanyama wala nyama hapo mwanzoni. Uwezekano wa dhana hii unategemea kiwango cha kuuwawa cha walao nyama, jambo hili kwa upande moja pia linaweza kuathiriwa na ukubwa wa mabadiliko ya mazingira katika kipindi hicho. Hivi karibuni upungufu wa idadi ya wanyama aina ya kongoni katika eneo la Laikipia, Kenya, umefanyika kwa usanjara na kuongezeka kwa simba miaka ishirini iliyopita. Kuelewa kana kwamba kupungua kwa kongoni kumechangiwa na kuongezeka kwa kuwindwa na simba, tulifuatilia takwimu muhimu za kongoni ambao walikuwa na ulinzi kiasi au kamili kutokana na simba. Kutengwa kwa simba kulibadilisha viwango vya ukuaji wa idadi ya kongoni kutoka hasi hadi chanya (λ = 0.89 ± 0.04 kulikokuwa na simba dhidi ya 1.11 ± 0.11 kulikotengwa simba), jambo hili ni dhabiti na matokeo ya utafiti wa demografia ya wanyama wala nyasi ambapo maisha ya wanayama wazima yalikuwa kiwango nyeti na muhimu. Uchambuzi wa matokeo ya majaribio ya jinsi maisha ya hawa wanyama yalivyo, ulibaini kuwa asilimia thelathini na mbili ya mabadiliko ya idadi yao ilitokana na uzaaji, jambo ambalo lilikuwa na madhara makubwa juu ya λ. Zaidi ya hayo, katika maeneo yaliyokuwa na simba, kongoni walipendelea zaidi mahali wazi (nyika) na kuepuka vichaka. Kazi yetu inatoa ushahidi wa majaribio na kuitikia wazo letu kuwa kupungua kwa kongoni kumechangiwa pakubwa na kurejeshwa kwa simba. Kutokana na kuongezeka kwa miti katika eneo la Laikipia kwa kipindi cha miaka hamsini iliyopita, tunashauri kwamba kupungua kwa idadi ya kongoni kutokana na simba kumechangiwa zaidi na mabadiliko ya mazingira.