Biodiversity in human-modified landscapes : case studies, the state of research, and implications for conservation

Abstract

Protected areas (PAs) cover 12.9% of Earth’s land, while just 5.8% has strict protection for biodiversity (Earth’s variety of ecosystems, species, and genetic variation). Constraints of size and configuration, mismanagement, anthropogenic pressure, and climate change hamstring the capacity of PAs to conserve biodiversity. Increasingly, studies of biodiversity in human-modified landscapes provide an evidence base to support policies to make land outside of PAs as amenable as possible for biodiversity persistence. I reviewed research on biodiversity in sub-Saharan Africa’s human-modified landscapes within four ecosystem categorizations: rangelands, tropical forest, Cape Floristic Region, and urban and rural built environment. I found potential for humanmodified landscapes to contribute to conservation across ecosystems. Available research could guide policy-making; nonetheless, several issues require further investment, e.g. research deficiencies, implementation strategies, and conflict with biodiversity. I also conducted case studies that could support land-use planning in South Africa’s coastal forest, part of a biodiversity hotspot. By comparing herpetofaunal communities over a land-use gradient, I found old-growth forest harbored the highest richness and abundance. Richness was low in sugar cane cultivation and degraded forest but substantial in acacia woodland and eucalyptus plantation. Composition differed between natural and anthropogenic vegetation types. Functional group richness decreased monotonically along the gradient, driven by sensitivity of fossorial herpetofauna and vegetation-dwelling frogs. Environmental variables were good predictors of frog abundance, but less so for reptiles. Maintaining forest and preventing degradation is important for herpetofaunal conservation while restoration and plantations have more value than cultivation. Old-growth remnants and post-disturbance regenerating vegetation also provide habitat for birds. However, occurrence does not ensure persistence. I calculated population trends for 37 bird species and general trends in overall bird density in different vegetation types. Seventy-six percent of species assessed have declined, 57% significantly so at an average rate of 13.9% per year. Overall, bird density fell at 12.2% per year across vegetation types. Changes in rainfall, habitat area, and survey coverage may partly explain trends. However, species with larger range extents declined more sharply than others and may be responding to environmental changes on a broad scale. These results cast doubt on the future persistence of birds in this human-modified landscape and justify further study. Such studies can support sensible land-use management; however, biases in study topics should not lead to gaps in the evidence base. By reviewing the global literature, I demonstrated clear geographical bias among biomes and geopolitical regions and taxonomic bias among species groups. Furthermore, distribution of published papers did not generally reflect threats of low PA coverage, high land conversion, and high human population density. Forests were the subject of 87% of papers, and 75% focused on the Americas and Europe, while Africa and Asia were critically understudied. This thesis highlights that managing human-modified landscapes for biodiversity could contribute to conservation. However, responses to land uses are complex, locationand species-specific, and often poorly understood, hindering integration of information into policy recommendations. Further research is needed to elucidate what, where, and how biodiversity persists alongside humans to enhance conservation efficacy, especially in understudied regions.