Refining the stress gradient hypothesis for mixed species groups of African mammals.

Species interactions such as facilitation and predation influence food webs, yet it is unclear how they are mediated by environmental gradients. Here we test the stress gradient hypothesis which predicts that positive species interactions increase with stress. Drawing upon spatially-explicit data of large mammals in an African savanna, we tested how predation risk and primary productivity mediate the occurrence of mixed species groups. Controlling for habitat structure, predation risk by lions and primary productivity affected the frequency of mixed species groups in species-specific ways, likely reflecting distinct stress perceptions. To test whether mixed species groups indicate positive interactions, we conducted network analyses for specific scenarios. Under predation risk, dyadic associations with giraffes were more pronounced and metrics of animal networks changed markedly. However, dyadic association and network metrics were weakly mediated by primary productivity. The composition of mixed species groups was associated with similarities in prey susceptibility but not with similarities in feeding habits of herbivores. Especially predation risk favoured the frequency of mixed species groups and pronounced dyadic associations which dilute predation risk and increase predator detection. While our results provide support for the stress gradient hypothesis, they also highlight that the relative importance of stressors is context-dependent.

Risk perception and tolerance shape variation in agricultural use for a transboundary elephant population.

To conserve wide-ranging species in human-modified landscapes, it is essential to understand how animals selectively use or avoid cultivated areas. Use of agriculture leads to human-wildlife conflict, but evidence suggests that individuals may differ in their tendency to be involved in conflict. This is particularly relevant to wild elephant populations. We analysed GPS data of 66 free-ranging elephants in the Serengeti-Mara ecosystem to quantify their use of agriculture. We then examined factors influencing the level of agricultural use, individual change in use across years and differences in activity budgets associated with use. Using clustering methods, our data grouped into four agricultural use tactics: rare (<0.6% time in agriculture; 26% of population), sporadic (0.6%-3.8%; 34%), seasonal (3.9%-12.8%; 31%) and habitual (>12.8%; 9%). Sporadic and seasonal individuals represented two-thirds (67%) of recorded GPS fixes in agriculture, compared to 32% from habitual individuals. Increased agricultural use was associated with higher daily distance travelled and larger home range size, but not with age or sex. Individual tactic change was prevalent and the habitual tactic was maintained in consecutive years by only five elephants. Across tactics, individuals switched from diurnal to nocturnal activity during agricultural use, interpreted as representing similar risk perception of cultivated areas. Conversely, tactic choice appeared to be associated with differences in risk tolerance between individuals. Together, our results suggest that elephants are balancing the costs and benefits of crop usage at both fine (e.g. crop raid events) and long (e.g. yearly tactic change) temporal scales. The high proportion of sporadic and seasonal tactics also highlights the importance of mitigation strategies that address conflict arising from many animals, rather than targeted management of habitual crop raiders. Our approach can be applied to other species and systems to characterize individual variation in human resource use and inform mitigations for human-wildlife coexistence.

Rethinking assessment of success of mitigation strategies for elephant-induced crop damage.

Crop damage is the most common impact of negative interactions between people and elephants and poses a significant threat to rural livelihoods and conservation efforts. Numerous approaches to mitigate and prevent crop damage have been implemented throughout Africa and Asia. Despite the documented high efficacy of many approaches, losses remain common, and in many areas, damage is intensifying. We examined the literature on effectiveness of crop-damage-mitigation strategies and identified key gaps in evaluations. We determined there is a need to better understand existing solutions within affected communities and to extend evaluations of effectiveness beyond measurement of efficacy to include rates of and barriers to adoption. We devised a conceptual framework for evaluating effectiveness that incorporates the need for increased emphasis on adoption and can be used to inform the design of future crop-damage mitigation assessments for elephants and conflict species more widely. The ability to prevent crop loss in practice is affected by both the efficacy of a given approach and rates of uptake among target users. We identified the primary factors that influence uptake as local attitudes, sustainability, and scalability and examined each of these factors in detail. We argue that even moderately efficacious interventions may make significant progress in preventing damage if widely employed and recommend that wherever possible scientists and practitioners engage with communities to build on and strengthen existing solutions and expertise. When new approaches are required, they should align with local attitudes and fit within limitations on labor, financial requirements, and technical capacity.

Replanteamiento de la Evaluación del Éxito de las Estrategias de Mitigación del Daño a Cultivos Causado por Elefantes Resumen El daño a los cultivos es el impacto más común generado por las interacciones negativas entre las personas y los elefantes. Actualmente representa una amenaza significativa para el sustento rural y los esfuerzos de conservación. Se han implementado numerosas estrategias para mitigar y prevenir el daño a los cultivos en toda África y Asia. A pesar de la documentación de la eficiencia de las estrategias, las pérdidas todavía son comunes y, en muchas áreas, el daño se está intensificando. Examinamos la literatura sobre la efectividad de las estrategias de mitigación del daño a cultivos e identificamos vacíos importantes en su evaluación. Determinamos que existe una necesidad por entender de mejor manera las soluciones existentes en las comunidades afectadas y por extender las evaluaciones de eficiencia más allá de las medidas de eficacia para que incluyan las tasas y barreras de la adopción. Diseñamos un marco de trabajo conceptual para la evaluación de la eficiencia, el cual incorpora la necesidad de un incremento en el énfasis de la adopción y puede usarse para informar a los diseñadores de las futuras evaluaciones de la mitigación de daños a cultivos causados por elefantes u otras especies conflictivas de manera más amplia. La capacidad de poder prevenir la pérdida de cultivos en práctica está afectada tanto por la eficiencia de una estrategia dada como por las tasas de aceptación entre los usuarios diana. Identificamos como los factores primarios que influyen sobre la aceptación a las actitudes locales, la sustentabilidad y la adaptabilidad, y examinamos cada uno de estos factores a detalle. Argumentamos que incluso las intervenciones moderadamente eficientes pueden llevar a cabo un progreso significativo en la prevención del daño si se emplean ampliamente. También recomendamos que, en donde sea posible, los científicos y los practicantes de la conservación participen con las comunidades para construir y fortalecer las soluciones y el conocimiento existentes. Cuando se requieran nuevas estrategias, éstas deberán alinearse con las actitudes locales y deberán encajar dentro de las limitaciones de la labor, los requisitos financieros y la capacidad técnica.