Related plant species respond similarly to chronic anthropogenic disturbance: implications for conservation decision-making.
Many developing countries harbour large numbers of species that face little-understood, gradual changes in their environment, including chronic anthropogenic disturbance (CAD), a high frequency but low intensity form of disturbance. These countries also lack the resources to study each species, so conservation practices have been generalized, assuming that complete taxonomic groups may be managed in the same ways. This approach could be justified if closely related species respond similarly to threats. We assessed if related species respond similarly to CAD, whether this affects phylogenetic diversity and if such patterns occur in different systems. Species' identity and abundance was recorded in 59 sites differing in CAD intensity in a semi-arid grassland and a tropical dry forest in Mexico. Disturbance response indices were calculated for each species. Nested analysis of variance coupled with null models were applied to determine if generalizations within taxa are justified and which taxonomic level explained the most variation in disturbance response among species. We obtained phylogenetic trees using molecular data for the grassland and published data for the tropical forest. Phylogenetic signal was measured with Pagel's λ. Community mean phylogenetic distance was regressed on CAD. Higher taxonomic levels explained more variation than expected by chance, indicating that related species respond similarly to CAD. However, only species in the same genus behaved similarly enough to make generalizations reliable. This is the result of an underlying, if modest, phylogenetic signal in CAD responses. Mean phylogenetic distance decreased with CAD in the grassland but not the tropical dry forest. This suggests that CAD was a stronger environmental filter in the grassland but weak in the tropical dry forest, where it was less intense. Policy implications. Species inform us how their relatives respond to chronic anthropogenic disturbance (CAD), supporting the idea that generalizations in management are possible. However, this procedure is seemingly reliable only within genera, which explain over 80% of the accumulated variance in species' CAD responses, and not within orders or families. CAD may reduce phylogenetic diversity, perhaps leading to ecosystem function loss.