Species Interactions Reverse Grassland Responses to Changing Climate K B Suttle et al Science 315 640 2007 DOI 10 1126 science 1136401 The following resources related to this article are available online at www sciencemag org this information is current as of February 10 2007 Supporting Online Material can be found at http www sciencemag org cgi content full 315 5812 640 DC1 A list of selected additional articles on the Science Web sites related to this article can be found at http www sciencemag org cgi content full 315 5812 640 related content This article cites 11 articles 5 of which can be accessed for free http www sciencemag org cgi content full 315 5812 640 otherarticles This article appears in the following subject collections Ecology http www sciencemag org cgi collection ecology Information about obtaining reprints of this article or about obtaining permission to reproduce this article in whole or in part can be found at http www sciencemag org help about permissions dtl Science print ISSN 0036 8075 online ISSN 1095 9203 is published weekly except the last week in December by the American Association for the Advancement of Science 1200 New York Avenue NW Washington DC 20005 Copyright c 2007 by the American Association for the Advancement of Science all rights reserved The title SCIENCE is a registered trademark of AAAS Downloaded from www sciencemag org on February 10 2007 Updated information and services including high resolution figures can be found in the online version of this article at http www sciencemag org cgi content full 315 5812 640 Species Interactions Reverse Grassland Responses to Changing Climate K B Suttle 1 Meredith A Thomsen 2 Mary E Power1 Predictions of ecological response to climate change are based largely on direct climatic effects on species We show that in a California grassland species interactions strongly influence responses to changing climate overturning direct climatic effects within 5 years We manipulated the seasonality and intensity of rainfall over large replicate plots in accordance with projections of leading climate models and examined responses across several trophic levels Changes in seasonal water availability had pronounced effects on individual species but as precipitation regimes were sustained across years feedbacks and species interactions overrode autecological responses to water and reversed community trajectories Conditions that sharply increased production and diversity through 2 years caused simplification of the food web and deep reductions in consumer abundance after 5 years Changes in these natural grassland communities suggest a prominent role for species interactions in ecosystem response to climate change I mpacts of recent climate change on plants and animals are already evident as geographic distributions shift poleward 1 2 and toward higher elevations 3 4 phenological events advance in time 5 7 and some species disappear altogether 8 With further climate change still expected prediction of future impacts has become critical to conservation planning and management To forecast ecological change under continued climate warming how1 Department of Integrative Biology University of California Berkeley CA 94720 USA 2Department of Biology University of Wisconsin La Crosse WI 54601 USA Present address Earth and Planetary Science University of California Berkeley CA 94720 USA To whom correspondence should be addressed E mail kbsuttle socrates berkeley edu ever we need a better understanding of the relative importance of direct responses by individual species to climate versus responses mediated by changing interactions with resources competitors pathogens or consumers 9 14 We imposed projected future precipitation regimes over grassland in northern California to evaluate the importance to ecosystem response of direct effects on grassland species versus indirect effects arising from species interactions Much of the California coastal region experiences a Mediterranean climate characterized by wet winters and long summer droughts Ecological responses to climate change in regions with Mediterranean climate regimes may be strongly driven by the redistribution of water in time and space 15 Changes in seasonal water Fig 1 A Bird s eye view of experimental communities in July 2002 A nearby road is visible as a gray strip top right Research described here is from 18 open grassland plots 18 additional plots were used in separate research B Schematic representation of an experimental plot shown as partitioned for measurement of plant biomass 30 900 cm2 640 2 FEBRUARY 2007 VOL 315 availability that affect plant phenology for example could lead to temporal mismatch between resource availability and consumer demand 16 which can have important effects on resource flow and ecosystem function 17 General circulation models developed at the Hadley Centre for Climate Prediction and Research HadCM2 and the Canadian Centre for Climate Modeling and Analysis CCM1 18 predict substantial increases in precipitation over most of California but differ in the projected seasonality of these increases The Hadley model calls for all additional rain to fall during the current winter rainy season whereas the Canadian model projects increased rainfall extending into the current summer drought The discrepancy between the two scenarios may be critical to the fate of grassland ecosystems in California where summer drought severely constrains plant growth and the timing of rainfall is more important to annual production and species composition than the amount 19 22 In 2001 we began a large scale rainfall manipulation in a northern California grassland to examine the consequences of these two projected regimes for production and diversity of grassland plants and invertebrates In a grassland at the Angelo Coast Range Reserve in Mendocino County California 39 44 17 7 N 123 37 48 4 W 18 circular 70 m2 plots were subjected to one of three watering treatments a winter addition of water January through March a spring addition of water April through June and an unmanipulated ambient control Fig 1 Each watered plot received about 44 cm of supplementary water over ambient rainfall per year roughly a 20 increase over mean annual precipitation but within natural variability in both amount and timing at the study site fig S1 We subplots small squares plant species richness two 2500 cm2 subplots large squares foliar and flying invertebrates two perpendicular sweep net
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