Reproductive seasonality in African ungulates in relation to rainfall

Abstract

Context. Reproductive seasonality in ungulates has important fitness consequences but its relationship to resource seasonality is not yet fully understood, especially for ungulates inhabiting equatorial environments.Aims. We test hypotheses concerning synchronisation of conception or parturition peaks among African ungulates with seasonal peaks in forage quality and quantity, indexed by rainfall.Methods. We relate monthly apparent fecundity and juvenile recruitment rates to monthly rainfall for six ungulate species inhabiting the Masai Mara National Reserve (Mara) of Kenya, using cross-correlation analysis and distributed lag non-linear models. We compare the phenology and synchrony of breeding among the Mara ungulates with those for other parts of equatorial East Africa, with bimodal rainfall and less seasonal forage variation, and for subtropical southern Africa, with unimodal rainfall distribution and greater seasonal forage variation.Key results. Births were more synchronised for topi, warthog and zebra than for hartebeest, impala and giraffe in the Mara, and for impala and hartebeest in southern than in eastern Africa. This pattern is likely to reflect regional differences in climate and plant phenology, hider-follower dichotomy and grazing versus browsing. All six species except the browsing giraffe apparently time the conception to occur in one wet season and births to occur just before the onset or during the next wet season, so as to maximise high-quality forage intake during conception and parturition. Fecundity and recruitment rates among the African ungulates peak at intermediate levels of rainfall and are reduced at low or excessive levels of rainfall. Fecundity rate is most strongly positively correlated with rainfall pre-conception, during conception and during early gestation, followed by rainfall at about the time of parturition for all the grazers. For giraffe, fecundity rate is most strongly correlated with rainfall during the gestation period.Conclusions. Rainfall seasonality strongly influences reproductive seasonality and juvenile recruitment among African ungulates. The interaction of the rainfall influence with life-history traits and other factors leads to wide interspecific and regional variation.Implications. Global climate change, especially widening annual rainfall variation expected to result from global warming, could reduce the predictability of the timing of peak forage availability and quality based on meteorological cues, the length of time with adequate nutrition or both, and hence reduce reproductive success among tropical ungulates.

Rainfall trends and variation in the Maasai Mara ecosystem and their implications for animal population and biodiversity dynamics

“…The predominantly deterministic and persistent primary rainfall cycles in the Mara likely have important implications for the dynamics and management of animal populations and their vegetation resources [ 5 , 14 ]. The changing periodicity in the rainfall oscillations and the increasing amplitude in the wet season rainfall oscillations in the Mara may compound impacts of the recurrent seasonal and cyclic variations in water and forage availability that animals already have to cope with by adaptively adjusting their reproduction, foraging and migration patterns.…”

“…Rainfall is the principal driver of the population dynamics of savanna herbivores [ 5 , 6 ] because it controls plant biomass production [ 7 , 8 ] and plant nutrient concentration [ 9 ], which affect herbivore birth [ 6 ] and survival [ 10 ] rates, susceptibility to predation [ 11 ] and, ultimately, biomass [ 12 , 13 ]. Not surprisingly, oscillatory dynamics in ungulate population size [ 5 ] and ungulate fecundity [ 14 ] are coupled with inter-annual and seasonal rainfall oscillations in African savannas, respectively.…”

Long-term historical and projected herbivore population dynamics in Ngorongoro crater, Tanzania

“…In the Serengeti-Mara ecosystem straddling Kenya and Tanzania, rainfall primarily drives population dynamics [11,12], aggregate population biomass [7,8], recruitment dynamics [13], phenology, synchrony and prolificacy of calving [14,15,16], seasonal dispersal and migration of large herbivores [17,18]. However, increasing frequency and intensity of droughts [19,20], widening variation of river flows [21] and rising temperatures [19] hasten the need to advance our understanding of how anticipated climate changes will likely affect larger herbivore populations.…”

How Rainfall Variation Influences Reproductive Patterns of African Savanna Ungulates in an Equatorial Region Where Photoperiod Variation Is Absent

“…Effective monthly fertility was related to monthly rainfall averaged over a time window spanning the month of conception identified by cross-correlation analysis and the distributed lag nonlinear model [ 8 ]. The effective monthly fecundity was grouped by the season (early wet, late wet and dry seasons) in which conception occurred to test the hypothesis that rainfall influences the likelihood of conceptions.…”

“…However, near the equator changing photoperiod is no longer a tenable cue for the timing of mating and hence conceptions. In these circumstances, many ungulate species reproduce year-round [ 6 , 7 , 8 ]. Nevertheless, certain ungulate species retain a seasonal birth pulse even in the absence of much day length variation, suggesting that other factors govern their reproductive phenology.…”