| dc.description.abstract | Physical ecosystem engineering is the process by which some species change the distribution of materials
and energy in ecosystems. Although several studies have shown that this process is a driver of local
species diversity, the current challenge is predicting when and where ecosystem engineering will have
large or small impacts on communities, while also explaining why impacts vary in magnitude across
engineer species and environments. This study addresses this issue and proposes a series of predictions
for these effects at the three spatial scales (the patch, the habitat and the landscape) along environmental
gradients of physical stress. The integrative prediction of this study was that the difference in species
diversity between engineered and unmodified situations (patches, habitats or landscapes) will increase
as the difference in physical stress between engineered and unmodified patches becomes larger. To test
the prediction, the effects of two well known high-Andean ecosystem engineers, the cushion plants
Azorella madreporica and Laretia acaulis, were assessed on plant species richness in central Chile. The
results support the main prediction, showing that ecosystem engineers have negative effects on species
diversity at sites when the environmental modifications they perform increase physical stress for other
species, while they have positive effects at sites where these habitat changes mitigate physical stress.
Then, the effects of the ecosystem engineers on species diversity seem to depend on the environmental
context, where larger environmental modifications are reflected in greater impacts, either positive or
negative, on species diversity. | |
