Large-scale changes in community composition: determining land use and climate change signals

Abstract

Human land use and climate change are regarded as the main driving forces of present-day and future species extinction. They may potentially lead to a profound reorganisation of the composition and structure of natural communities throughout the world. However, studies that explicitly investigate both forms of impact--land use and climate change--are uncommon. Here, we quantify community change of Dutch breeding bird communities over the past 25 years using time lag analysis. We evaluate the chronological sequence of the community temperature index (CTI) which reflects community response to temperature increase (increasing CTI indicates an increase in relative abundance of more southerly species), and the temporal trend of the community specialisation index (CSI) which reflects community response to land use change (declining CSI indicates an increase of generalist species). We show that the breeding bird fauna underwent distinct directional change accompanied by significant changes both in CTI and CSI which suggests a causal connection between climate and land use change and bird community change. The assemblages of particular breeding habitats neither changed at the same speed and nor were they equally affected by climate versus land use changes. In the rapidly changing farmland community, CTI and CSI both declined slightly. In contrast, CTI increased in the more slowly changing forest and heath communities, while CSI remained stable. Coastal assemblages experienced both an increase in CTI and a decline in CSI. Wetland birds experienced the fastest community change of all breeding habitat assemblages but neither CTI nor CSI showed a significant trend. Overall, our results suggest that the interaction between climate and land use changes differs between habitats, and that comparing trends in CSI and CTI may be useful in tracking the impact of each determinant.

Figure 1. Locations of the study plots of the Dutch Breeding Bird Monitoring Programme.

Figure 2

Time lag analysis of Hellinger transformed Dutch bird abundances for the complete breeding bird fauna (A), and for breeding bird communities in forests (B), farmland (C), dunes and coast (D), heath (E) and wetland (F) between 1984 and 2009. Dotted lines represent the linear regressions of Hellinger distance on square root transformed time lag. The respective slopes, b, are reported within each panel. All p are <0.0001. Slopes sharing superscripts are not different at p<0.05.

Figure 3. Temporal trend of the community temperature index of the entire Dutch breeding bird fauna (bold line) and for breeding bird communities in forests, farmland, dunes and coast, heath and wetland between 1984 and 2009.

Figure 4. Temporal trend of the community specialisation index of the entire Dutch breeding bird fauna (bold line) and for breeding bird communities in forests, farmland, dunes and coast, heath and wetland between 1984 and 2009.

Figure 5. Comparison of the slope of time lag analysis (TLA) and the temporal trends of the community temperature index (CTI) and the community specialisation index (CSI) of the entire Dutch breeding bird fauna and breeding bird communities in forests, farmland, dunes and coast, heath and wetland.