Fertility partially drives the relative success of two introduced bovines (Bubalus bubalis and Bos javanicus) in the Australian tropics

Abstract

Context Some large herbivores introduced to Australia have achieved population densities so high as to cause considerable ecological damage. Intriguingly, others have been relatively less successful and have correspondingly perturbed their new environments less. An excellent example is two similar-sized bovine species that established feral populations in the Northern Territory of Australia in the mid-19th century. Asian swamp buffalo (Bubalus bubalis) rapidly colonised the tropical savannas, causing ecological degradation, especially on freshwater swamps. In contrast, banteng (Bos javanicus) are restricted to their point of introduction and have caused relatively negligible ecological damage. Understanding the reasons of this differential success is of theoretical and applied interest and contributes to managing large herbivore populations for ex situ conservation and feral-animal control. Aims To compare the population structure of buffalo and banteng on the basis of shot samples, so as to construct life tables for four contemporary (low-density) buffalo populations, and collated data from previous work from three historical (high-density) buffalo populations and one banteng population (the only extant ex situ population in existence). Further, to provide a validation of age estimation with and without informed priors in a Bayesian model comparing horn length and ages estimated from tooth cementum annuli. Finally, to interpret our results in the context of relative invasion potential of the two bovid species. Key Results For both species, survival of juveniles was the most important demographic component influencing deterministic population growth. However, buffalo have the demographic capacity to recover swiftly after control because of high survival and fertility rates across a range of population densities. Fertility of buffalo was historically greater than that of banteng, and buffalo fertility increased as their populations were reduced. Conclusions These findings highlight how subtle differences in demographic rates and feeding ecology can influence the success (high population growth and range expansion) of large herbivores, knowledge which is increasingly important for managing invasive species effectively. Implications We show that that individual life-history traits and demographic performance, especially fertility, play an important role in determining the spread of invasive bovids in a novel environment.

Turning Pests into Profits: Introduced Buffalo Provide Multiple Benefits to Indigenous People of Northern Australia

“…In the annually harvested population at Bulman, juvenile survival made a higher proportional contribution (0.516) to population growth than adult survival (0.23) or adult fertility (0.17) or juvenile fertility (0.08) (McMahon et al 2010a). Most females of breeding age were reproductively Bold number indicate age-classes from which female buffalo are harvested (i.e.…”

“…Indeed buffalo are an excellent low-maintenance resource because unlike cattle, they can maintain body condition and positive growth during times of low food or quality (Ford 1978(Ford , 1982Moran 1986Moran , 1992. In addition to their ability to maintain good body condition under variable environmental situations, buffalo (unlike commercial cattle in northern Australia) have high annual reproductive rates (McCool 1992) and females continue to reproduce until their maximum age-approximately 17 years (McMahon et al 2010a). Although buffalo are well-adapted to poor environments (Ford 1978(Ford , 1982McMahon et al 2010a;Moran 1986Moran , 1992, their calves are vulnerable to extended periods of harsh conditions.…”

“…In addition to their ability to maintain good body condition under variable environmental situations, buffalo (unlike commercial cattle in northern Australia) have high annual reproductive rates (McCool 1992) and females continue to reproduce until their maximum age-approximately 17 years (McMahon et al 2010a). Although buffalo are well-adapted to poor environments (Ford 1978(Ford , 1982McMahon et al 2010a;Moran 1986Moran , 1992, their calves are vulnerable to extended periods of harsh conditions. For example, increased juvenile mortality has been linked to the delayed onset of the monsoon season because buffalo rely heavily on the drinking water and germinated forage produced by late dry season rains (Freeland and Choquenot 1990).…”

“…Our simple approach of using a system dynamics model is not as sophisticated as matrix modelling approaches employed in predictive models of wild populations . Nevertheless, our model is populated with robust demographic data (McMahon et al 2010a), obtained from seven populations of swamp buffalo across the Northern Territory, and is complemented by previous research (Boulton and Freeland 1991;Freeland and Boulton 1990). Indeed, our simulations give similar results to those obtained by Boulton and Freeland (1991) who developed a discrete-time model of extinction risk based on aerial control programs.…”

More analytical bite in estimating targets for shark harvest

“…In the absence of any published information on population status we recalculated S based on 3 different finite population growth rates: λ = 0.9, 1.0 and 1.1 to determine the sensitivity of the mortality estimates to assumptions associated with rate of population change (cf. McMahon et al 2011); variation in survival using these different values was negligible (data not shown), so we defaulted to the assumption of λ = 1.0.…”