 Reference Base  Reproduction and population density: trade-offs for the c... |
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Rachlow, J.L.; Berger, J., 1998. Reproduction and population density: trade-offs for the conservation of rhinos in situ. Animal Conservation 1 (2): 101-106, figs. 1-3, table 1
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Conservation |
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White Rhino |
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Females breed faster in low-density populations than in high density - Conservation Implication for rhino managers
Due to extreme levels of poaching, few African rhinos now persist outside of heavily guarded reserves. Most rhino sanctuaries encompass relatively small areas because of the difficulty and expense of providing adequate anti-poaching protection in large, remote regions. Because rhino populations within these sanctuaries are likely to increase in the absence of poaching until density-dependent factors stabilise population growth, managers may eventually trade off reproduction for safety in following this conservation strategy.
One way around this dilemma is to maintain populations in reserves below ecological carrying capacities. Indeed, management plans for rhinos in South Africa and Namibia have incorporated these ideas based on theoretical relationships between population growth and density. The long-term data from Matobo Park provide empirical results to quantify such relationships, and demonstrate that density-dependent responses can have profound effects, even within a period of 30 years.
Maintenance of rhino populations in reserves at low densities, however, presents managers with another challenge. Because large-bodied species require large areas, total population sizes of rhinos within smaller reserves are likely to be low, and few will reach numbers recommended for long-term population viability. This situation already exists for black rhinos, for which >80 % of the remaining individuals survive in populations of fewer than 100 animals. Under these circumstances, managers may need to consider exchanging individuals among reserves in a metapopulation management approach. However, translocation of rhinos is both costly and logistically challenging.
Non-biological factors also will bear on management decisions. Conservationists concerned about populations threatened by poaching may be constrained by limited resources for law enforcement, and may choose to maintain surviving individuals in higher-density populations within safe areas. From a numerical viewpoint, trading off numbers lost to poachers with the decrease in numbers of young recruited, this conservative strategy may be more prudent until resources can be secured to establish additional sanctuaries. However, if management goals are to increase numbers of rhinos and to restock safe areas within their former ranges, then population densities within rhino sanctuaries should be monitored and managed below the level where body condition affects reproduction.
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