Climatic variability, resource availability, and anthropogenic impacts heavily influence an animal's home range. This makes home range size an effective metric for understanding how variation in ...environmental factors alter the behavior and spatial distribution of animals. In this study, we estimated home range size of African elephants (Loxodonta africana) across four sites in Namibia, along a gradient of precipitation and human impact, and investigated how these gradients influence the home range size on regional and site scales. Additionally, we estimated the time individuals spent within protected area boundaries. The mean 50% autocorrelated kernel density estimate for home range was 2200 km2 95% CI:1500–3100 km2. Regionally, precipitation and vegetation were the strongest predictors of home range size, accounting for a combined 53% of observed variation. However, different environmental covariates explained home range variation at each site. Precipitation predicted most variation (up to 74%) in home range sizes (n = 66) in the drier western sites, while human impacts explained 71% of the variation in home range sizes (n = 10) in Namibia's portion of the Kavango‐Zambezi Transfrontier Conservation Area. Elephants in all study areas maintained high fidelity to protected areas, spending an average of 85% of time tracked on protected lands. These results suggest that while most elephant space use in Namibia is driven by natural dynamics, some elephants are experiencing changes in space use due to human modification.
We analyze the largest dataset of collared elephants ever recorded in Namibia to determine the relative importance of humans and environmental variables in shaping elephant movements. We found that human activities are influencing elephant space use at some sites, though regional trends are still driven by precipitation and vegetation productivity.
Connectivity conservation is aimed at sustaining animal movements and ecological processes important to ecosystem functioning and the maintenance of biodiversity. However, connectivity conservation ...plans are typically developed around a single species and rarely empirically evaluated for their relevance to others, thereby limiting our understanding of how connectivity requirements differ across species.
We used an omnidirectional application of circuit theory and GPS data from six species to evaluate connectivity at multiple scales for multiple species within the world's largest transfrontier conservation landscape in southern Africa. We evaluated the effects of linear barriers, natural habitat types and anthropogenic land use on movement. We identified multispecies connectivity hotspots as areas where current flow was concentrated or channelled through pinch points. To evaluate surrogate species for connectivity, we evaluated the correspondence among single‐species connectivity across the entire landscape and also examined whether a more localized corridor for African savanna elephant Loxodonta africana captured high multispecies connectivity values.
Connectivity models revealed many intact areas across the landscape with diffuse current flow, but also evidence that fences, rivers, roads and areas of anthropogenic use acted as strong barriers to movement—particularly in the case of fences, which completely blocked female elephant movement. Tests of correspondence among single‐species connectivity models revealed spotted hyaena and African wild dog as the strongest surrogate species of connectivity. Female elephants were found to be the weakest surrogate species of connectivity at the landscape scale. However, focusing within a localized elephant corridor revealed the areas of concentrated or channelled connectivity for most species in our study.
Synthesis and applications. Our results suggest that the single‐species focus permeating connectivity literature may result in conservation plans that poorly conserve the connectivity needs of co‐occurring species. Our study also highlights the importance of testing the efficacy of surrogate species for connectivity at multiple scales. We recommend evaluating multispecies connectivity to prioritize areas for conservation that safeguard the connectivity needs of multiple species of conservation concern.
Our results suggest that the single‐species focus permeating connectivity literature may result in conservation plans that poorly conserve the connectivity needs of co‐occurring species. Our study also highlights the importance of testing the efficacy of surrogate species for connectivity at multiple scales. We recommend evaluating multispecies connectivity to prioritize areas for conservation that safeguard the connectivity needs of multiple species of conservation concern.
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Understanding rhino movement behavior, especially their recursive movements, holds significant promise for enhancing rhino conservation efforts, and protecting their habitats and the biodiversity ...they support. Here we investigate the daily, biweekly, and seasonal recursion behavior of rhinos, to aid conservation applications and increase our foundational knowledge about these important ecosystem engineers.
Using relocation data from 59 rhinos across northern Namibia and 8 years of sampling efforts, we investigated patterns in 24-h displacement at dawn, dusk, midday, and midnight to examine movement behaviors at an intermediate scale and across daily behavioral modes of foraging and resting. To understand recursion patterns across animals' short and long-term ranges, we built T-LoCoH time use grids to estimate recursive movement by each individual. Comparing these grids to contemporaneous MODIS imagery, we investigated productivity's influence on short-term space use and recursion. Finally, we investigated patterns of recursion within a year's home range, measuring the time to return to the most intensively used patches.
Twenty four-hour displacements at dawn were frequently smaller than 24-h displacements at dusk or at midday and midnight resting periods. Recursion analyses demonstrated that short-term recursion was most common in areas of median rather than maximum NDVI values. Investigated across a full year, recursion analysis showed rhinos most frequently returned to areas within 8-21 days, though visits were also seen separated by months likely suggesting seasonality in range use.
Our results indicate that rhinos may frequently stay within the same area of their home ranges for days at a time, and possibly return to the same general area days in a row especially during morning foraging bouts. Recursion across larger time scales is also evident, and likely a contributing mechanism for maintaining open landscapes and browsing lawns of the savanna.
Factors affecting intraspecific variation in home range size have rarely been examined using modern statistical and remote sensing methods. This is especially true for animals in seasonal savanna ...environments in Africa, despite this biome’s importance for both conservation and development goals. We studied the impacts of spatial and temporal variability in environmental conditions, along with individual and social factors, on home range sizes in African buffalo (
Syncerus caffer
) in northeastern Namibia. Our data set spans 4 years, is derived from 32 satellite tracking collars, and contains over 35,000 GPS locations. We used the local convex hull method to estimate home range size from 31 buffalo captured at 6 sites. We used a variety of remotely sensed data to characterize potential anthropogenic and natural boundaries, as well as seasonal and temporal heterogeneity in environmental conditions. Using an information-theoretic, mixed effects approach, our analyses showed that home ranges varied over two orders of magnitude and are among the largest recorded for this species. Variables relating to vegetation and habitat boundaries were more important than abiotic environmental conditions and individual or social factors in explaining variation in home range size. The relative contributions of environmental, individual, social, and linear boundary variables to intraspecific home range size have rarely been examined and prior to this had not been assessed for any species in seasonal savannas of Africa. Understanding the factors that condition space-use patterns of wildlife in this area will lead to better-informed conservation and sustainable development decisions.
Success of animal translocations depends on improving postrelease demographic rates toward establishment and subsequent growth of released populations. Short-term metrics for evaluating translocation ...success and its drivers, like postrelease survival and fecundity, are unlikely to represent longer-term outcomes. We used information theory to investigate 25 years of data on black rhinoceros (Diceros bicornis) translocations. We used the offspring recruitment rate (ORR) of translocated females—a metric integrating survival, fecundity, and offspring recruitment at sexual maturity—to detect determinants of success. Our unambiguously best model (AICω = 0.986) predicted that ORR increases with female age at release as a function of lowerpostrelease adult rhinoceros sex ratio (males:females). Delay of first postrelease reproduction and failure of some females to recruit any calves to sexual maturity most influenced the pattern of ORRs, and the leading causes of recruitment failure were postrelease female death (23% of all females) and failure to calve (24% of surviving females). We recommend translocating older females (≥6 years old) because they do not exhibit the reproductive delay and low ORRs of juveniles (<4 years old) or the higher rates of recruitment failure of juveniles and young adults (4-5.9 years old). Where translocation of juveniles is necessary, they should be released into female-biased populations, where they have higher ORRs. Our study offers the unique advantage of a long-term analysis across a large number of replicate populations—a science-by-management experiment as a proxy for a manipulative experiment, and a rare opportunity, particularly for a large, critically endangered taxon such as the black rhinoceros. Our findings differ from previous recommendations, reinforce the importance of long-term data sets and comprehensive metrics of translocation success, and suggest attention be shifted from ecological to social constraints on population growth and species recovery, particularly when translocating species with polygynous breeding systems. El éxito de la reubicación de animales depende del mejoramiento de las tasas demográficas después de la reubicación para establecer y hacer crecer a las poblaciones liberadas. No es probable que las medidas de corto plazo para evaluar el éxito de una reubicación y sus conductores, como la supervivencia y fecundidad post-liberación, representen resultados a largo plazo. Utilizamos teoría de la información para investigar 25 años de datos sobre reubicaciones del rinoceronte negro (Diceros bicornis). Usamos la tasa de reclutamiento de crías (TRC) de las hembras reubicadas - una medida que integra la supervivencia, la fecundidad y el reclutamiento de las crías en la madurez sexual - para detectar determinantes del éxito. Nuestro mejor modelo (AICω = 0.986) pronosticó que la TRC incrementa con la edad de las hembras al momento de la liberación como función de una proporción más baja de sexos en rinocerontes adultos después de la liberación (machosihembras). El retraso de la primera reproducción post-reubicación y el fracaso de algunas hembras en reclutar mínimo a una cría hasta la madurez sexual influyeron más sobre el patrón de TRCs, y las principales causas del fracaso de reclutamiento fueron la muerte post-liberación de la hembra (23% de todas las hembras) y el fracaso de parto (24% de las hembras sobrevivientes). Recomendamos reubicar a las hembras más viejas (≥ 6 años) porque no exhiben el retraso reproductivo ni las TRCs bajas de las juveniles (<4 años) o las tasas más altas de fracaso de reclutamiento de las juveniles y las adultas jóvenes (4 - 5.9 años). En donde sea necesaria la reubicación de juveniles, éstas deberían ser liberadas en poblaciones con mayoría de hembras disponibles sexualmente, en donde tienen mayores TRCs. Nuestro estudio ofrece la ventaja única de un análisis de largo plazo en un gran número de poblaciones replicadas - un experimento de ciencia-por-manejo como sustituto de un experimento manipulativof y una rara oportunidad, particularmente para un taxón grande y en peligro crítico como es el rinoceronte negro. Nuestros resultados difieren de recomendaciones previas, refuerzan la importancia de los conjuntos de datos de largo plazo y de las medidas comprensivas del éxito de una reubicación, y sugieren que la atención se cambie de las limitaciones ecológicas a las limitaciones sociales que tienen el crecimiento pobladonal y la recuperación de la especie, particularmente cuando se reubiquen especies con sistemas de reproducción poliginios. 动物放归行动的成功取决于放归后种群统计参数的提高，以促进放归种群的成功建群和随后的种群增 长。评估放归成功与否及其驱动カ的短期指标, 如放归后的存活率和繁殖力，不太可能反映长期的后果。我们 用信息论的方法分析了黑犀牛(Diceros bicomis) 25 年的放归数据，并用放归雌性的后代补充率 (ORR) 一一 个整合了存活率、繁殖力及性成熟时后代补充情况的指标，来探讨放归成功的决定因素。我们确定的最优模型 (AICω = 0.986) 预测在较低的成年犀牛性比難: 雌性) 情況下’ ORR 随着放归时雌性年龄的增加而增加。放 归后第一次繁殖的延迟以及ー些雌性没有获得达到性成熟年龄的后代对ORR 的模式影响最大,种群补充失败最 主要的原因是放归后雌性的死亡（占所有雌性的 23%) 以及产仔失败（占存活雌性的24%) 。我们建议放归时选 择年龄较大郎岁 (≥6岁) 的雌性’ 因为它们没有表现出延迟繁殖, 而亚成体 (<4岁) 具有低的 ORR，或亚成体及年轻 成年雌性 (4-5.9岁) 具有较高的后代补充失败率。当必须放归亚成体时, 应将它们释放到偏雌性的种群中，这样 它们会有更髙的 ORR。我们的研究为大量放归种群的长期分析提供了独特的优势一即基于管理的科学实验作 为操纵实验的替代，以及难得的研究机会，特別是对于像黑犀牛这样大型极度瀕危的类群。我们的結果有别于前 人的建议’ 强调了建立长期数据集和衡量放归成功的综合指标的重要性,同时建议将注意力从种群增长和物种恢 复的生态限制因素转移到社会限制因素上，特别是当放归一夫多妻婚配制度的物种时。
Partial migration (when only some individuals in a population undertake seasonal migrations) is common in many species and geographical contexts. Despite the development of modern statistical methods ...for analyzing partial migration, there have been no studies on what influences partial migration in tropical environments. We present research on factors affecting partial migration in African buffalo (Syncerus caffer) in northeastern Namibia. Our dataset is derived from 32 satellite tracking collars, spans 4 years and contains over 35,000 locations. We used remotely sensed data to quantify various factors that buffalo experience in the dry season when making decisions on whether and how far to migrate, including potential man-made and natural barriers, as well as spatial and temporal heterogeneity in environmental conditions. Using an information-theoretic, non-linear regression approach, our analyses showed that buffalo in this area can be divided into 4 migratory classes: migrants, non-migrants, dispersers, and a new class that we call "expanders". Multimodel inference from least-squares regressions of wet season movements showed that environmental conditions (rainfall, fires, woodland cover, vegetation biomass), distance to the nearest barrier (river, fence, cultivated area) and social factors (age, size of herd at capture) were all important in explaining variation in migratory behaviour. The relative contributions of these variables to partial migration have not previously been assessed for ungulates in the tropics. Understanding the factors driving migratory decisions of wildlife will lead to better-informed conservation and land-use decisions in this area.
The Nile crocodile, Crocodylus niloticus, is found throughout sub-Saharan Africa, including Namibia, Botswana and Angola. The species was transferred from CITES Appendix I to Appendix II in 2004, ...although it is recognized as peripherally endangered in Namibia due to diminishing habitat availability primarily from human encroachment. In 2013, a species management plan was approved in Namibia to assess the management of the Namibian Nile crocodile populations. During 2012, an aerial survey was conducted to provide an estimate of Nile crocodile population numbers. A recently developed N-mixture model for estimation of abundance and spatial variation was used. Detection probability correlated to animal size and environmental covariates. Our data also suggest that small crocodiles are easier to detect during the spring. The abundance for different size classes was influenced by river complexity (vegetation, depth, channels) and the distribution of human settlements. An estimated 806 individuals were counted along the 352 km Namibian portion of the Kunene River system with a conservative estimate of 562 crocodiles regardless of size. The parameter estimates generated by the analysis suggested that the class-structured model can produce reliable estimates of total abundance and of local abundance for this section in the Kunene River system.
Nile crocodiles are apex predators widely distributed in sub-Saharan Africa that have been viewed and managed as a single species. A complex picture of broad and fine-scale phylogeographic patterns ...that includes the recognition of two species (Crocodylus niloticus and Crocodylus suchus), and the structuring of populations according to river basins has started to emerge. However, previous studies surveyed a limited number of samples and geographical regions, and large areas of the continent remained unstudied. This work aimed at a fine scale portrait of Nile crocodile populations at the fringes of their geographic distribution in southern Africa. Wild and captive individuals were sampled across four major river systems (Okavango, Lower Kunene, Lower Shire and Limpopo) and the KwaZulu-Natal region. A multi-marker approach was used to infer phylogeographic and genetic diversity patterns, including new and public mitochondrial data, and a panel of 11 nuclear microsatellites. All individuals belonged to a phylogenetic clade previously associated with the C. niloticus species, thus suggesting the absence of C. suchus in southern Africa. The distribution of mitochondrial haplotypes indicated ancestral genetic connectivity across large areas, with loss of diversity along the north-south axis. Genetic variation partitioned the populations primarily into western and eastern regions of southern Africa, and secondarily into the major river systems. Populations were partitioned into five main groups corresponding to the Lower Kunene, the Okavango, the Lower Shire, and the Limpopo rivers, and the KwaZulu-Natal coastal region. All groups show evidence of recent bottlenecks and small effective population sizes. Long-term genetic diversity is likely to be compromised, raising conservation concern. These results emphasize the need for local genetic assessment of wild populations of Nile crocodiles to inform strategies for management of the species in southern Africa.
Wildlife-based tourism poses opportunities and challenges for species conservation. Minimizing potential negative impacts of tourism is critical to ensure business and conservation enterprises can ...coexist. In north-western Namibia tourism is used as a conservation tool for the Critically Endangered black rhinoceros Diceros bicornis. However, black rhinoceroses are susceptible to human disturbance and may become displaced by tourist activities, which threatens not only the security and health of the rhinoceros population but also the sustainability of the business. We examined areas avoided by black rhinoceroses to understand how they respond to the type and extent of tourism development, and to evaluate management alternatives. We used spatial data on use of water sources by rhinoceroses to create a series of a priori candidate models that described the negative influences of tourist activities on rhinoceros habitat use. A model selection approach strongly supported a cumulative zones of influence model comprised of a 6 km buffer around the airstrip combined with a 1 km buffer around roads used daily. We compared alternative management scenarios using the best-performing model and found that an optimal road-use policy combined with airstrip relocation could minimize the total area avoided by the black rhinoceros to 7.1% and loss of high quality habitat to 20.7%. Under the worst-case scenario the area avoided and loss of high quality habitat were 153 and 85% greater, respectively, than under the scenario with optimal management. Our findings provide a novel framework and a practical, policy-relevant decision support tool to improve the contribution of tourism to wildlife conservation.
Species translocations are remarkable experiments in evolutionary ecology, and increasingly critical to biodiversity conservation. Elaborate socio-ecological hypotheses for translocation success, ...based on theoretical fitness relationships, are untested and lead to complex uncertainty rather than parsimonious solutions. We used an extraordinary 89 reintroduction and 102 restocking events releasing 682 black rhinoceros (Diceros bicornis) to 81 reserves in southern Africa (1981-2005) to test the influence of interacting socio-ecological and individual characters on post-release survival. We predicted that the socio-ecological context should feature more prominently after restocking than reintroduction because released rhinoceros interact with resident conspecifics. Instead, an interaction between release cohort size and habitat quality explained reintroduction success but only individuals' ages explained restocking outcomes. Achieving translocation success for many species may not be as complicated as theory suggests. Black rhino, and similarly asocial generalist herbivores without substantial predators, are likely to be resilient to ecological challenges and robust candidates for crisis management in a changing world.
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