Balancing biodiversity and agriculture
Modern agriculture has revolutionised the planet’s capacity to support humans, yet has simultaneously had a greater negative impact on biodiversity than any other human activity. Balancing the demand for food with the conservation of biodiversity is one of the most pressing issues of our time. While these concerns are relevant globally, there is an urgent need to conduct research of this nature in the developing world, characterised by high population growth rates and rapid agricultural development. This project focuses on providing the evidence to underpin better planning of production landscapes to offset the negative effects of agriculture on biodiversity in southern Africa. Post-doc Chevonne Reynolds is tackling this question in collaboration with Claire Spottiswoode, Res Altwegg of the Statistics in Ecology, Environment and Conservation group in the Department of Statistical Sciences, and Andrew Balmford of the University of Cambridge.
Is a land-sharing or a land-sparing strategy best for conserving southern African birds? These two strategies represent alternatives whereby conservation and production are integrated in space (“land-sharing”) or separated in space (“land-sparing”). Advocates of land-sparing suggest that although land-sharing is beneficial within farmland, if it reduces yield then a larger area must be farmed to meet any given production target. However, the merits of each strategy are still hotly debated, in part because this question is typically addressed by short-term field studies that ignore processes relevant to biodiversity occurring at larger scales.
Making use of the remarkable South African Bird Atlas Project 2 (SABAP2) dataset, Chevonne is assessing how agricultural land-use patterns affect bird populations, and ultimately which strategy is best suited to the conservation of southern Africa’s bird diversity. Combining the SABAP2 data with fine-scale data on agricultural land-use, Chevonne has investigated how the amount and configuration of farmland within each pentad (~ 9 x 7 km) affects the relative population density of bird species using occupancy models. She conducted the analysis across three separate biomes in South Africa to determine whether bird populations respond in a consistent way across regions and therefore whether results can be extrapolated to other landscapes. Her fascinating findings suggest that different strategies prevail based on the structure of the native vegetation and the type of agricultural product that is farmed. Within grasslands for example, a greater proportion of the bird community benefits from land-sharing farming practices, while in contrast bird communities of coastal forest rely on land-sparing and the preservation of large patches of native vegetation. Remarkably, agricultural land conversation is not all doom and gloom, and several endemic species, particularly in the fynbos, appear to be reliant on agricultural land. Here, it is possible that agricultural production is mimicking ecological processes once carried out by megafauna that are now largely extinct from the region. This research highlights once again that successful conservation approaches are context dependent and that one-size-fits-all conservation strategies are not able to address the challenge of protecting biodiversity in agricultural landscapes.
Chevonne is also collaborating with researchers at the University of Florida and the University of Swaziland to investigate how landscape heterogeneity in agricultural mosaics affects biodiversity. A key feature of the developing world is that agriculture is typically interspersed among other land-uses, creating heterogeneous landscapes. While there is evidence that landscape heterogeneity positively influences biodiversity, the application of this hypothesis is hindered by a lack of understanding of which components of landscape heterogeneity drive these effects, and at what spatial scale(s). We also need to know whether diverse taxonomic groups are similarly affected before we can apply this hypothesis as a general conservation strategy in agricultural mosaics. Chevonne led a team of international students to collect data on several taxonomic groups in the savanna-sugarcane mosaics of north-eastern Swaziland in June and July 2017.
The theme for the second year of the project was connectivity, and working at the interface between savanna and agriculture, both intensive sugarcane farming and less intensive subsistence farming, they tested how birds, dung beetles, rodents and even trees could move between the land-use types. As expected the results varied among taxonomic groups, however one key finding relating to birds was that smaller species with short wings are more limited in their dispersal ability. These findings suggest that certain species may become isolated in savanna fragments as agriculture expands, limiting connectivity across populations.
Activities in 2017
- Chevonne Reynolds continued as a Post-doctoral researcher on the project. She completed the initial analyses and started preparing manuscripts for publication.
- Continued collaboration between the Fitz and the Statistics in Ecology, Environment and Conservation (SEEC) research group.
- Teaching and training of the University of Swaziland and University of Florida students on field and research techniques.
- Two papers resulting from Chevonne’s team’s research in Swaziland were published in the journals Landscape Ecology and Insect Conservation and Diversity. An additional paper is in revision at Biodiversity and Conservation and three others are in preparation.
- Chevonne was appointed as a lecturer at the University of the Witwatersrand from January 2018, but will remain a member of the Fitz Centre of Excellence.
Impact of the project
Using ecological and life-history traits to explore species responses to agriculture we hope to develop a generalizable framework to help conservation planners, farmers and policy makers improve management for biodiversity in production landscapes.
DST-NRF CoE grant; National Science Foundation (USA).
Prof. Claire Spottiswoode (FIAO, UCT and U. Cambridge)
Dr Chevonne Reyolds (FIAO, UCT)
Prof. Res Altwegg (SEEC, UCT)
Prof. Andrew Balmford (U. Cambridge)
Prof. Bob McCleery (U. Florida)
Prof. Ara Monadjem (U. Swaziland)