Plant biodiversity in an anthropogenic biosphere

Background/Question/Methods Humans have altered or replaced native ecosystems across more than three quarters of the terrestrial biosphere, creating new global patterns of biodiversity as a result of native species extinctions and the introduction of nonnative domesticates and invasive species. While native plant species richness follows global patterns in climate and terrain, anthropogenic global patterns of plant species richness are poorly understood. Here we explore these global patterns using a combination of existing data and spatial models for native species richness, the loss of native species caused by habitat loss, and species increases caused by nonnative invasions and the introduction of domestic plants. Results/Conclusions Results indicate that humans have significantly altered plant species richness across more than 92% of the terrestrial biosphere (in terms of ice-free land area), either by causing a loss of more than 5% of native species or by increasing nonnative species to 5% or more of native species richness. Though humans have caused more than 45% of the terrestrial biosphere to lose more than 5% of its native species (global median loss = 4%), nonnative species gains represent the largest anthropogenic global change in plant species richness. More than 91% of the terrestrial biosphere gained nonnative species at levels of 5% or more of native richness, with a global median gain of 9%. Gains in nonnative species exceeded native losses across more than three quarters of the terrestrial biosphere, and nonnative gains tended to balance out and even overcompensate for native losses, as evidenced by a strong global relationship between losses and gains (log/log regression R2 = 0.36). As a result, anthropogenic global patterns of species richness (natives – losses + gains) appeared to follow pre-existing native patterns, with native patterns predicting global variation in anthropogenic species richness with ten times the power (0.93) of invasive species gains (0.09), ornamental species introductions (0.08), anthropogenic species losses (0.07) and crop species introductions (0.03), based on standardized coefficients from multiple log/log regression. While anthropogenic patterns of plant species richness resembled native patterns and generally showed net gains in species richness, these patterns represent net losses of native species locally and globally and their replacement by nonnatives, and are accompanied by substantial declines in species evenness. Improved global data and models of anthropogenic biodiversity are essential for ecological science and sustainable stewardship of the terrestrial biosphere.