A reappraisal of the role of humans in the biotic disturbance of islands

Abstract

SUMMARYTraditionally, islands have been used as ecological and biogeographical models because of their assumed ecological simplicity, reduced ecosystem size and isolation. The vast number of Earth's oceanic islands play a key role in maintaining global biodiversity and serve as a rich source of evolutionary novelty. Research into the factors determining diversity patterns on islands must disentangle natural phenomena from anthropogenic causes of habitat transformation, interruption and enhancement of biological fluxes and species losses and gains in these geographically and ecologically limited environments. The anthropogenic ecological forcing of communication through global transport has profound implications regarding island–continent links. Anthropogenic disturbances along continental margins and insular coasts contribute to shaping island biotas in ecological time, but also have evolutionary consequences of global resonance. Patterns of human landscape and resource use (geographical space and ecological communities and species), as well as increasing ecological connectivity of oceanic islands and mainland, are chief driving forces in island biogeography that should be reappraised. Global indirect effects of human activities (i.e. climate change) may also affect islands and interact with these processes. We review the implications of direct and indirect anthropogenic disturbances on island biotic patterns, focusing on island size, isolation and introduced exotic species, as well as the unsettled issue of oceanic island ecological vulnerability.

Land-use and related pressures have reduced biotic integrity more on islands than on mainlands

“…A significantly higher human pressure on islands than on mainland regions has previously been suggested by Kier et al, (2009), who used the Human Impact Index (Sanderson et al, 2002), as measure of current threat (largely referring to the year 2000). Islands' small size can facilitate the access to remote areas with remaining primary vegetation (Kier et al, 2009) and brings a higher human population density in close proximity to natural habitats (Delgado et al, 2017), making islands more vulnerable to habitat loss. The steep declines in local island (but not mainland) richness as human population increases and proximity to roads decreases suggest that species native to islands may have greater need of 'people-free space' than those on mainlands;; while the widespread land conversion on islands suggests that many do not get it.…”

The impacts of local networks on subsistence resilience and biodiversity in a low-lying Moluccan reef system between 1600 and the present

“…The data and arguments presented here are consistent with a pattern that has been demonstrated by others on how small island ecosystems have been fundamentally reshaped through declining non-anthropic biodiversity, invasive colonisation of non-native species, changes in physical landscape, seismic instability, coastal erosion and sea-level rise. Much of this degradation results from human activities, although resource management has been shown to enhance productivity and sustainability (Braje et al 2017, Delgado et al 2017). We now know that islands such as those in the Geser–Gorom corridor are far from isolated biologically, being dynamic and open systems, living organisms moving across their boundaries, and islands interacting with each other.…”

“…We now know that islands such as those in the Geser–Gorom corridor are far from isolated biologically, being dynamic and open systems, living organisms moving across their boundaries, and islands interacting with each other. The smaller the island, the more intense and frequent the disturbance, the more human activity exacerbates the influence of sea-level rise, extreme weather events (high tides and flooding), hurricanes, earthquakes and volcanism (Delgado et al 2017, p. 373).…”

Anthropogenic disturbances and conservation of coastal environments in an oceanic archipelago

“…Thus, many of them are threatened biodiversity hotspots and their contribution to global biodiversity is of paramount relevance (Myers et al, 2000, Kueffer andKinney 2017). Climatic and oceanographic variables, mainly currents and prevailing winds, along with distance to mainland (remoteness), location regarding frequented trade routes, which is a today's proxy for effective isolation (Helmus et al, 2014, Delgado et al, 2017, and island attributes such as island origin and type (Nunn et al, 2016), topography, area and elevation (Brown and Lomolimo 1998;Whitakker and Fernández-Palacios 2007) are main determinants for the colonization of islands by species from the adjacent continents or other islands. The interaction of these features with geographical and anthropogenic factors also confers susceptibility for alien species invasions and human occupation (Russell et al, 2017).…”