Future directions

useful for further understanding bio-mechanical constraints on foraging behavior (Boukal, 2014). Given each of these considerations, it now seems feasible to extend current scaling frameworks to integrate allometric scaling relationships across levels of organization, from the physiology and morphology of individuals to trophic interactions and ultimately to the energetics of entire communities and ecosystems (Eklöfet al., 2013; Klecka & Boukal, 2013).

2.4. Future directions

Globally, insects are an important functional component of terrestrial and freshwater systems, often with strong economic and cultural importance for humans (Yang &

Gratton, 2014). By integrating body-size related information such as physiological constraints (as characterized by the MTE — Brownet al.(2004); Schramskiet al.(2015)

— or competing approaches — Harrisonet al.(2014); Chownet al.(2007)), together with body-size relationships for consumer-resource pairs (Brose et al., 2006) and entire food webs (Riedeet al., 2011; Digel et al., 2011), ecologists now have a better understanding of ecosystem stability and functioning. Thus, patterns in insect body size distributions, together with intra-specific and inter-specific allometric relationships, are important for a wide range of basic and applied questions. For instance, allometric effects can explain how predator loss in soil-litter systems affects crucial ecosystem functions such as litter decomposition and nutrient cycling (Schneideret al., 2012). Moreover, intraspecific size distributions apparently have far-reaching consequences at the community level (Rudolf

& Rasmussen, 2013; Jochum et al., 2012), but most often these data are not available.

Therefore, there is a need for continued development of highly-resolved empirical datasets, such as population body size distributions for multiple interacting species (Gouws et al.

(2011); Dellet al.(2015)) or body-mass variation across various levels of insect phylogeny Chown & Gaston (2010). Insect-specific analyses of subsets of existing data bases for species interactions (e.g. Dell et al. (2011); Rall et al. (2012)) are a logical next step. Future research on individual-level interactions of insects from a diverse range of ecosystems might then shed light on important ecosystem mechanisms, providing a deeper understanding of how crucial ecological functions are organized and maintained. One particularly useful approach appears to be novel automated methods (Dellet al., 2014a), which should help elucidate the mechanistic link between individual-level, morphologically and physiologically constrained behavior and higher levels of ecological and biological organization.

A generalized version of allometric theory needs to be developed that is able to account for apparent non-size related variation, by incorporating additional behavioral and functional morphological traits. The first steps toward this goal have already been made in

quantitative studies of food webs and other ecological networks: for instance, Naisbitet al.

(2012) used a ‘two-dimensional’ approach where phylogenetic relatedness could explain food-web structure better than body size alone. In addition, Eklöf et al. (2013) showed that the structure of different types of ecological networks are best explained by models that incorporate approximately three to four additional traits (e.g. habitat type, mobility, phenology, phylogenetic information; Eklöf et al. (2013)) together with body size. Here again, functional morphology was explicitly highlighted (e.g. fruit size and bill gape for frugivorous birds; Eklöf et al. (2013)). Additional traits and relationships that should be incorporated into an extended framework of ecological allometry in insects include environmental temperature (e.g. Brownet al.(2004); Dellet al.(2014b, 2011); Rallet al.

(2012)), the degree of hunger of predators (Simpson & Raubenheimer, 2000) and their experience with handling particular prey (Raine & Chittka, 2008), the stoichiometry of food resources (Shurin et al., 2006), and even the individual ‘personality’ of predators (Kalinkat, 2014; Modlmeier et al., 2015). Thus, a full and mechanistic understanding of insect ecology will only be achieved by approaches that integrate both size and (apparent) non-size effects (Boukal, 2014). We particularly encourage approaches addressing the link between allometric constraints on behavior with functional morphology and foraging relationships to gain a better understanding of the processes that shape the typical hump-shaped relationship between predator–prey size ratios and capture success (Gergs & Ratte, 2009; Kalinkat et al., 2013; Brose, 2010). Although this topic has been investigated with vertebrates (e.g. Kiltie (2000); Healyet al.(2013); Domenici (2001)), a similar integration of such relationships is required for insects and other invertebrates.

Future research at the intersection between insect behavioral and community ecology should therefore embrace, and ultimately integrate, these approaches to establish a new framework that links distinct layers of biological and ecological organization.

Acknowledgments

G.K. was supported through the Leibniz Competition (SAW-2013-IGB-2) and by a postdoctoral fellowship from the German Academic Exchange Service (DAAD). M.J. was funded by the Deutsche Forschungsgemeinschaft (DFG) SFB990/1. Funding bodies had no involvement in the planning or writing of this manuscript, nor in the decision to submit it for publication. We thank Walter Jetz for sharing the original data used in Figure 2.2 c. We would also like to thank Jacintha Ellers and Cécile Le Lann for the invitation to contribute to this issue and two anonymous reviewers for their insightful comments on an earlier version of the manuscript.

Chapter 3.

Consequences of tropical land use for multitrophic biodiversity and ecosystem functioning

Andrew D. Barnes*, Malte Jochum*, Steffen Mumme, Noor Farikhah Haneda, Achmad Farajallah, Tri Heru Widarto & Ulrich Brose

* These authors contributed equally to this work.

This chapter is licensed under a Creative Commons Attribution 4.0 International License.

Abstract

Our knowledge about land-use impacts on biodiversity and ecosystem functioning is mostly limited to single trophic levels, leaving us uncertain about whole community biodiversity-ecosystem functioning relationships. We analyse consequences of the globally important land-use transformation from tropical forests to oil-palm plantations. Species diversity, density, and biomass of invertebrate communities suffer at least 45% decreases from rainforest to oil palm. Combining metabolic and food-web theory, we calculate annual energy fluxes to model impacts of land-use intensification on multitrophic ecosystem functioning. We demonstrate a 51% reduction in energy fluxes from forest to oil-palm communities. Species loss clearly explains variation in energy fluxes, but this relationship depends on land-use systems and functional feeding guilds, whereby predators are the most heavily affected. Biodiversity decline from forest to oil palm is thus accompanied by even stronger reductions in functionality, threatening to severely limit the functional resilience of communities to cope with future global changes.