Species richness of hornworts and liverworts on islands: A preliminary analysis of geographic and anthropogenic drivers
Author
Kropp, Rebecca MagdalenaDate
2021Abstract
Environmental factors related to geography and climate are generally among
the most significant drivers of species richness across spatial and temporal scales.
Among the most studied attributes explaining patterns of species richness on
islands are island area and geographic isolation, the two main factors that founded
the Theory of Island Biogeography by MacArthur and Wilson (1967). Even though
their theory of the equilibrium on islands represents a generally testable and
applicable model, its simplicity disregards taxa specific traits like long distance
dispersal capacities and abiotic factors like climate. Furthermore, the impact of
human activity which is known to affect biodiversity at different spatial scales, from
global to regional, is not included in the model. Bryophytes and especially
hornworts and liverworts have comparatively broad distribution ranges due to great
long distance dispersal abilities and are known to respond very sensitively to
environmental changes which is why pointed as one of the most efficient taxonomic
groups used as bioindicators of climate change. Based on a compilation of floristic
data from a selection of islands distributed worldwide we investigate the
significance of various environmental attributes for patterns in species richness of
hornworts and liverworts on islands. We include a set of predictor variables
consisting in geographic (distance to the mainland coast, area, proportion of
surrounding landmass, latitude, longitude, maximum elevation), climatic (mean
annual temperature, mean annual precipitation, climate change velocity and intraannual seasonality quantified by using the minimum annual temperature range and
the minimum coefficient of variation in monthly precipitation) and one sociodemographic variable (human population density) to determine what factors explain
best variation in species richness across the 95 islands studied. Our results indicate
that besides island area and isolation, the traditional geographical variables,
elevation, variation in precipitation and climate change velocity are important drivers
of species richness of hornworts and liverworts on islands. In contrast, human
population density did not seem to explain patterns of species richness. Despite
these results, we conclude that different families of predictors, including past
ecological conditions and human activities, may explain patterns in species
richness, which cannot be explained by traditional geographic conditions alone.