Notes Ecology, 96(3), 2015, pp. 873–878 Ó 2015 by the Ecological Society of America Long-term declines in nutritional quality of tropical leaves JESSICA M. ROTHMAN, 1,2,9 COLIN A. CHAPMAN, 3,4 THOMAS T. STRUHSAKER, 5 DAVID RAUBENHEIMER, 6 DENNIS TWINOMUGISHA, 7 AND PETER G. WATERMAN 8 1 Department of Anthropology, Hunter College of the City University of New York, New York, New York 10065 USA 2 New York Consortium in Evolutionary Primatology, New York, New York 10065 USA 3 Department of Anthropology, McGill University, Montreal, Quebec H3A 2T7 Canada 4 Wildlife Conservation Society, Bronx, New York 10460 USA 5 Department of Evolutionary Anthropology, Duke University, Durham, North Carolina 27708 USA 6 Charles Perkins Centre, University of Sydney, Sydney, Australia 7 Department of Biology, Makerere University, Kampala, Uganda 8 Centre for Phytochemistry and Pharmacology, Southern Cross University, East Lismore, New South Wales 2480 Australia Abstract. Global change is affecting plant and animal populations and many of the changes are likely subtle and difficult to detect. Based on greenhouse experiments, changes in temperature and rainfall, along with elevated CO 2 , are expected to impact the nutritional quality of leaves. Here, we show a decline in the quality of tree leaves 15 and 30 years after two previous studies in an undisturbed area of tropical forest in Kibale National Park, Uganda. After 30 years in a sample of multiple individuals of ten tree species, the mature leaves of all but one species increased in fiber concentrations, with a mean increase of 10%; tagged individuals of one species increased 13% in fiber. After 15 years, in eight tree species the fiber of young leaves increased 15%, and protein decreased 6%. Like many folivores, Kibale colobus monkeys select leaves with a high protein-to-fiber ratio, so for these folivores declining leaf quality could have a major impact. Comparisons among African and Asian forests show a strong correlation between colobine biomass and the protein-to-fiber ratio of the mature leaves from common tree species. Although this model, predicts a 31% decline in monkey abundance for Kibale, we have not yet seen these declines. Key words: climate change; folivores; global warming; leaf chemistry; nutritional ecology; primates; tropical foliage. INTRODUCTION The Earth’s climate has warmed by approximately 0.68C over the past 100 years, and some estimates suggest that the climate could warm by a further 0.38 to 6.48C this century (IPPC 2007). There have been numerous documented shifts in phenology, distribution, population abundance, life history, and species demog- raphy in response to climate change (Pounds et al. 1999, Hannah et al. 2002, IPPC 2007, Newman et al. 2011). These impacts are driven partly by direct effects of climate change on species (e.g., responses to tempera- ture), but there is increasing evidence that the indirect effects, mediated via species interactions, could accen- tuate or buffer these impacts (Angert et al. 2013). An important potential indirect effect on herbivores and higher trophic levels is the influence of changing climates on the nutritional quality of vegetation (Coley et al. 2002). Much of what we know about how plant chemistry responds to changes in CO 2 levels and temperature are based on greenhouse and free-air CO 2 enrichment experiments (Zvereva and Kozlov 2006, Stiling and Cornelissen 2007, Robinson et al. 2012). A meta- analysis of grasses, herbs, and trees suggests that elevated atmospheric CO 2 is associated with an average increase in nonstructural carbohydrate concentration of 39%, and decreased protein ( 10%) and structural carbohydrates ( 13%). However, there was also an increase in toughness across plants under elevated CO 2 in the laboratory (Robinson et al. 2012). Toughness is associated with presence of structural carbohydrates, such as cellulose (Westbrook et al. 2011, Kitajima et al. 2012). The source experiments from the meta-analysis were not uniform, sometimes showing opposite trends, and the variance was often better explained when interacting effects, such as soil nutrient status and Manuscript received 24 February 2014; revised 18 August 2014; accepted 27 August 2014. Corresponding Editor: T. P. Young. 9 E-mail: jessica.rothman@hunter.cuny.edu 873