DOI: 10.5061/dryad.j9kd51chz
title: Data from: Evaluating temporal turnover in avian species richness in a Mediterranean semiarid region: different responses to elevation and forest cover

description: Aim. When studying the effects of global change on biodiversity, it is far
 more common for the effects of climate change and land-use changes to be
 assessed separately rather than jointly. However, the effects of land-use
 changes in recent decades on species richness in areas affected by climate
 change have been less studied. We assess the temporal turnover in
 species richness of an avian community between a historical period and a
 modern one as a consequence of global change. Location. Semiarid
 Mediterranean ecosystem (Southeastern Spain). Method. We fitted a
 hierarchical multi-species occupancy model for each period
 (1991-1992, and 2012-2017), obtaining avian species-specific estimates of
 occupancy probability in relation to environmental covariates (elevation
 and forest cover). We analyze the relationships between changes in the
 bird community and environmental variables, analysing the temporal
 turnover of the species richness and the richness-based species-exchange
 ratio. Results. The estimated species richness accounting for
 detectability was higher than observed species richness, and decreased in
 the more recent period. Following our hypotheses, we observed a dual
 pattern of species richness increase associated with different elevations,
 showing different species turnover rates due to the joint effects of
 climate change and land-use change. There is a trend toward greater
 species richness with higher elevations that is associated with climate
 change, where the species turnover rate is low. Also, species richness
 increased towards lower elevations, but with a high turnover rate. The
 latter can be due to species expansions throughout new habitat
 configurations in bordering forest systems associated with anthropic
 land-use changes. Conclusions. Our study is of great interest to
 understand the temporal turnover of avian species richness associated with
 areas experiencing both climate and land-use change.
description: This field work was developed
 as a basis for assessing the state of the region's forest heritage
 and the effects of global change on its biodiversity, concentrated in two periods: a
 "historical period" (years 1991 and 1992) and a "modern
 period" (years 2012 and 2017). The survey protocol was characterized
 by transects of 1 kilometer length, which were distributed across all the
 forested areas in the study area in a random fashion and were surveyed
 once during a breeding period (May-July). Each transect survey was conducted by walking
 and recording the number of each species detected (by sight or song/call)
 along it. A total of 377 1-km transects were conducted for the historical
 period as part of a forestry plan in the region, developing a new avian
 survey of 198 transects with a similar protocol for the modern
 period. We considered the 1-km transects of each bird
 survey as nested within a "site", i.e., as spatial observations
 replicated within the site, thus enabling estimation of detection
 probability in an occupancy model. We defined sites as cells in a grid that
 covers our study area. We
 selected cell size to be 2x2 km, based on the species in our bird
 community (most of them passerines with small home
 ranges), which may be suitable for evaluating the
 effects of environmental covariates on bird species occupancy at a
 regional scale.
 Therefore, a total of 377
 and 198 1-km spatial transects were conducted and grouped in 226 and 139
 sites for the historical and modern periods,
 respectively. 
description: Dataset contains two R data files for the historical and the actual
 period, respectively. Both datasets contain a list with: * Matrix Ysum
 with the number of spatial replicates (i.e., the detection frequency) for
 each site i where the species k (with the species code) was observed is
 recorded in the matrix Ysum. * nsite: number of sampling sites. * Vector
 nrep contains the number of spatial replicates per site (note that it does
 not vary among species). * nspec: number of species. * Vector forest:
 normalized covariate (percentage of forest cover) for each sampled site. *
 Vector alt: normalized covariate (elevation, meters m.) for each sampled
 site.