Spatial determinants of food web structure and function, from landscape to global scales

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How do food webs change over space? One the one hand, distant food webs may contain different species because of differences in the local environment or limited dispersal. Such differences in food webs may be extreme when they are so far apart as to draw from different species pools. On the other hand, even though species composition differs, the traits of the species may remain the same, such that food webs “work” the same way. Resolving the effects of space on the structure and functioning of food webs is critical for understanding how large-scale stressors (e.g. climate change, forest fragmentation) affect food webs. To resolve how space affects food webs, we need to (a) replicate experiments over landscape and continental scales, to determine how dispersal or biogeography changes species or traits; (b) expose such replicated food webs to environmental change, like altered climate, and reduced dispersal, such as occurs in isolated forest fragments; and (c) transplant species or even food webs between sites, to separate site-differences in species traits from the environment.******In this proposal I present such a research program, based on the macroinvertebrates (largely immature insects) found in the water-filled axils of tropical bromeliads. These small systems (typically <1L) can occur at high density and are therefore important contributors to the carbon budget and biodiversity of tropical forests. Importantly for this proposal, bromeliads occur widely across landscapes and continents (North, Central and South America). I co-ordinate a network of 45 researchers who work on this system throughout its range. ******My research program considers how climate change, forest fragmentation, dispersal and the species pool affect the structure and functioning of bromeliad food webs at landscape to continental scales. To study climate change, we will first use elevation as a proxy, as today's mid-elevation climate is expected to be the future's high-elevation climate. We will also focus on rainfall, expected to change more than temperature in the Neotropics, and its impact on bromeliad food webs. To study fragmentation, we will use treeholes - a system very similar to bromeliads as bromeliad densities in our fragments are too spotty. To study dispersal, we will apply methods from population genetics to many species in the food web. To study effects of the species pool, we will conduct replicated experiments in Costa Rica, Puerto Rico, French Guiana and Brazil and compare compiled food web data over 11 countries (in both cases making use of the research network). Finally, we will also manipulate the traits at the top of food webs (predators) and at the bottom of food webs (dead leaves) to help understand how the food web functions. ******In sum, this research proposal provides a blueprint for understanding how food webs function at landscape and global scales, and how environmental change may disrupt that functioning. **