Human pressure as an ecological force across scales and systems

Abstract

Historically, climate has been seen as the main driver of global vegetation patterns, but ecological paradigms have recently expanded to acknowledge human activity as a critical determinant of species biogeography. Today, human land use is the primary direct anthropogenic driver of global biodiversity decline, but not all species respond in the same way. How do species differentially respond to direct human disturbance and to climate? And how do the importance of these factors compare? I investigate these questions through the lens of species inherent characteristics (life form and life history) in different systems (flowering plants and fish) across multiple scales. Drawing on publicly available global databases, I integrate data on climate and different forms of human pressure to assess how these forces compare across dimensions of biodiversity. I investigate: how human land use compares to climate in driving plant life form occurrence and abundance (global); how cumulative human pressure compares to climate in affecting spatial patterning in endemic European plant species (continental); how climate compares to fishing pressure in affecting fish community life history strategy in the North East Atlantic (regional), and how nutrient addition and abandonment of traditional management practises impact productivity, diversity and community composition in a unique high diversity Irish grassland (hyper-local). Across scales and systems, I find that direct human influence is a factor affecting ecological patterns, and that the relative influence of different ecological drivers depends on the extent and resolution at which they are studied. Climate and human disturbance act in tandem as filters shaping the realised niches of species through space. Additionally, human disturbance may produce more divergent outcomes than climate across species inherent traits, contracting the niche of species with slower life history and expanding the niche of disturbance tolerant species. My findings highlight the urgent need to include direct human disturbance in all investigations of fundamental ecological patterns, and to explicitly consider the scale at which are ecological questions are being asked. If biodiversity is to be protected, and broad patterns of life in space and time understood, we must consider ecology within the context of pervasive human influence.