Consequences of Climate Warming and Altered Precipitation Patterns for Plant-Insect and Multitrophic Interactions

Abstract

Understanding and predicting the impacts of anthropogenically driven climate change on species interactions and ecosystem processes is a critical scientific and societal challenge. Climate change has important ecological consequences for species interactions that occur across multiple trophic levels. In this Update, we broadly examine recent literature focused on disentangling the direct and indirect effects of temperature and water availability on plants, phytophagous insects, and the natural enemies of these insects, with special attention given to forest ecosystems. We highlight the role of temperature in shaping plant and insect metabolism, growth, development, and phenology. Additionally, we address the complexity involved in determining climate-mediated effects on plant-insect and multitrophic level interactions as well as the roles of plant ecophysiological processes in driving both bottom-up and top-down controls. Climate warming may exacerbate plant susceptibility to attack by some insect groups, particularly under reduced water availability. Despite considerable growth in research investigating the effects of climate change on plants and insects, we lack a mechanistic understanding of how temperature and precipitation influence species interactions, particularly with respect to plant defense traits and insect outbreaks. Moreover, a systematic literature review reveals that research efforts to date are highly overrepresented by plant studies and suggests a need for greater attention to plant-insect and multitrophic level interactions. Understanding the role of climatic variability and change on such interactions will provide further insight into links between abiotic and biotic drivers of community- and ecosystem-level processes. Anthropogenic activities have led to rapid and unprecedented increases in atmospheric carbon dioxide (CO2) and other greenhouse gases, which in turn have resulted in numerous observable climatic changes, such as elevated temperature, increased frequency and severity of extreme weather events (e.g. heat waves and droughts), and altered precipitation patterns (e.g. decreased snow cover) (National Research Council, 2010). Species are responding to these climate change factors, as demonstrated by shifts in phenology (the timing of key biological and life history events), biogeographic ranges, and ecological interactions (Bale et al., 2002; Parmesan and Yohe, 2003; Hegland et al., 2009; Robinson et al., 2012). In this Update, we review and discuss the consequences of climate change on plant-insect and multitrophic interactions. Specifically, we address the direct and indirect effects of climate warming and altered precipitation patterns on plants, phytophagous insects, and higher trophic level organisms. We focus on these two components of climate change, firstly, because temperature is the abiotic factor that most directly influences insects (Bale et al., 2002), and secondly, because water availability plays a prominent role in mediating plant-insect interactions (Mattson and Haack, 1987; Huberty and Denno, 2004). Moreover, heat and drought are often interconnected climatic stressors. While other global change drivers, such as elevated CO2 and ozone, also have significant consequences for plant-insect and multitrophic interactions, those effects are beyond the scope of this Update and have been have been recently reviewed elsewhere (e.g. Lindroth, 2010; Robinson et al., 2012). Over the last century, average global surface air temperatures have increased by 0.81°C, and climate models project an additional 1.1°C to 6.4°C increase by the end of the 21st century, with stronger warming trends in terrestrial habitats and at higher latitudes (see National Research Council, 2010 and references therein for observed and predicted patterns discussed here). In addition to elevated mean temperatures, climate models predict an increase in the frequency and intensity of extreme warming events, such as heat waves. Beyond these global warming trends, climate change patterns demonstrate strong seasonal and regional signals. For example, mean winter temperatures in the Midwest and northern Great Plains of the United States have increased by 4°C over the past 30 years. Compared with temperature, observations for precipitation are more variable, demonstrating mean annual increases as well as decreases at regional scales and across seasons. In general, climate model predictions for changes in precipitation are more uncertain than for temperature. However, some specific projections related to precipitation are considered to be robust, including expected increases in the total area of land affected by drought, the number of dry days annually, and the risk of drought in snowmelt dominated ecosystems. Globally, the land area affected by drought has doubled since 1970, according to historical Palmer Drought Index data. Decreased snowpack is also a well-established consequence of global climate change, a