In this post Associate Editor, Elizabeth Nichols and student, Jordan Reyes comment on the recent paper by Alvarado et al.,The role of livestock intensification and landscape structure in maintaining tropical biodiversity, published in Journal of Applied Ecology.
The United Nations predicts that by the year 2050 the world population will have increased by 34%, reaching nearly 9.7 billion people. How can we support this growing human population while maintaining biological diversity? While a new recipe for sustainable landscape management is clearly needed, less obvious are the required ingredients for such multifunctional landscapes. In their recent Journal of Applied Ecology paper, Alvarado and colleagues provide a shopping list.
The authors offer novel insight into the ways in which both landscape structure and human management of livestock production systems influence community assemblages of dung beetles – a diverse insect group with important functional roles in both natural and managed systems. To do this, they apply a multi-scale, comparative landscape approach to assess whether and how the richness, diversity, abundance, biomass, and composition of dung beetle communities varied with landscape structure and the intensification of livestock production. In the northeast region of Mexico’s Yucatan Peninsula, Alvarado and colleagues identified 20 independent 1-km2 focal landscapes, each dominated by one of five distinct land-use types: large forest fragments, traditional cattle ranches, silvopastoral systems, intensified livestock production systems, or maize production. After conducting a supervised land-use classification, they mapped all landscapes at three distinct spatial scales – 1, 2 and 3.5-km2. At each spatial scale, they quantified landscape structure as percent native forest cover, degree of fragmentation, and edge density. To quantify livestock production intensification, they estimated net cattle production (kilograms of edible protein per hectare per year), annual livestock dung production, and conducted interviews with landowners to estimate the annual application of anti-helminthic drugs (macrocyclic lactones) administered to cattle. After placing 25 pitfall traps in each landscapes (500 traps in total) and identifying the resulting 169,00 captured individuals (in 33 species), the researchers were able to draw conclusions about the relative influences of livestock intensification and landscape structure on dung beetles community assemblages at multiple spatial scales.
Alvarado and colleagues first discovered that dung beetle species richness, diversity, and abundance most clearly responded to landscape structure at the 3.5-km2 spatial scale, while beetle biomass response to landscape structure was consistent across all spatial scales. Additionally, while measures of landscape structure were better predictors of dung beetle species diversity, richness, and biomass than livestock intensification measures, dung beetle abundance was more strongly related to livestock intensification. Of landscape structure measures, forest cover was the best predictor of all aspects of dung beetle community structure, demonstrating a positive association with species diversity, richness, biomass, and abundance. Finally, among the livestock intensification variables, the administration of macrocyclic lactones to livestock demonstrated a strong negative association with beetle diversity, richness, abundance, and biomass.
These results bring us a series of insights into the main drivers of biodiversity in human-modified tropical landscapes. First, the findings of Alvarado et al. support previous studies about the importance of tropical forest fragments in the maintenance of dung beetle diversity in livestock-dominated landscapes. Second, the authors report that landscape context strongly influences the effects of on-farm livestock management for biodiversity, and that the use of anti-helminthic treatments for cattle has a strong negative impact at the community level for dung beetles. The combination of these two results carries perhaps the most interesting policy implication of their study. The authors suggest that the preference of dung beetles for large forest remnants (relative to other land uses) implies that land-sparing strategies will promote dung beetle conservation in the Neotropics. Yet in order to maintain agricultural production, land-sparing approaches often come hand-in-hand with higher intensity land-use in those areas dedicated to agricultural and livestock production. Given that Alvarado and colleagues demonstrate that higher intensity livestock production that relies heavily on the use of anti-helminthic drugs has devastating consequences for dung beetle populations, a new research and management imperative becomes rather clear. We must improve our understanding of how to achieve increased livestock yields whilst reducing the negative on-farm impacts of intensification practices for biodiversity. Such techniques may include investments in the research, development and distribution of dung beetle-friendly macrocyclic lactones, or advancements in understanding how to incorporate dung beetles themselves in the biological control of helminth parasites of cattle.
Overall, the findings of Alvarado and colleagues clarify how we may better manage landscape structure and livestock production in ways that result in more synergies and less trade-offs. Such efforts are a critical component of ongoing efforts to plan for and manage multifunctional and resilient landscapes that maintain both biodiversity and the range of ecosystem services critical for human health, wealth, and wellbeing.