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The importance of competition in phytphagous insect communities is a highly controversial and unresolved issue. This debate was resolved, in part, by the recognition that species may compete indirectly as well as directly. I first test the importance of direct competition on the fitness of L. helianthi and C. platyptera with a series of laboratory experiments which manipulate the densities of each species. I focus on the leafminers Liriomyza helianthi and Calicomyza platyptera because these two leafminer species co-occur spatiotemporally, are closely related, and share a cryptic feeding niche, and, are therefore predicated to compete and provide a model system for testing the assumptions of competition theory. Liriomyza helianthi and C. platyptera along with their community of hymenopteran parasitoids provide a model system for studying apparent competition in the field. Apparent competition, one indirect pathway for competition, is defined as a negative effect of one species on the population growth rate or abundance of another species, mediated through the action of shared natural enemies. I surveyed populations of L. helianthi and C. platyptera, along with their community of parasitoids, over two years at seven sites in the Central Valley of California. Quantitative food webs for each year were used to visualize host-parasitoid interactions. I found the same dominant parasitoids were shared by both species of herbivore. Parasitism of C. platypera, was significantly positively correlated with L. helianthi leaf-miner density and parasitism levels. Indirect interactions can extend herbivore competition across space and time. Apparent competition has generated much recent attention, but studies that test the mechanisms that lead to apparent competition are still rare. I use experimental data to test hypotheses on the mechanisms leading to asymmetric apparent competition. Liriomyza helianthi populations emerge approximately one month (two parasitoid generations) before C. platyptera and have a higher population density throughout the season. Experimental removal of L. helianthi populations in the early summer leads to a 50% reduction in parasitism of C. platyptera. Because parasitoids are known to be important mortality agents in this system, I conclude that emergence asynchrony between the two herbivore species significantly impacts populations of C. platyptera. Land-use intensification has led to a mosaic landscape which juxtaposes human-managed and natural areas. In such human-dominated and heterogeneous landscapes, spillover across habitat types, especially in systems which differ in resource availability, may be an important ecological process structuring communities. While there is much evidence for spillover from natural habitats to managed areas, little attention has been given to flow in the opposite direction. Here we synthesize studies from five functionally important trophic groups, herbivores, pathogens, pollinators, predators, and seed dispersers, and discuss evidence for spillover from managed to natural systems in all five groups. I argue that this effect has been underestimated in the past. The most frequently documented examples of spillover from managed to natural systems report pathogen and vertebrate predator spillover, with a smaller number of examples reporting spillover of pollinators and herbivores.

Ecologists have traditionally focused on herbivore carcasses as study models in scavenging research. However, some observations of scavengers avoiding feeding on carnivore carrion suggest that different types of carrion may lead to differential pressures. Untested assumptions about carrion produced at different trophic levels could therefore lead ecologists to overlook important evolutionary processes and their ecological consequences. Our general goal was to investigate the use of mammalian carnivore carrion by vertebrate scavengers. In particular, we aimed to test the hypothesis that carnivore carcasses are avoided by other carnivores, especially at the intraspecific level, most likely to reduce exposure to parasitism. We take a three-pronged approach to study this principle by: (i) providing data from field experiments, (ii) carrying out evolutionary simulations of carnivore scavenging strategies under risks of parasitic infection, and (iii) conducting a literature-review to test two predictions regarding parasite life-history strategies. First, our field experiments showed that the mean number of species observed feeding at carcasses and the percentage of consumed carrion biomass were substantially higher at herbivore carcasses than at carnivore carcasses. This occurred even though the number of scavenger species visiting carcasses and the time needed by scavengers to detect carcasses were similar between both types of carcasses. In addition, we did not observe cannibalism. Second, our evolutionary simulations demonstrated that a risk of parasite transmission leads to the evolution of scavengers with generally low cannibalistic tendencies, and that the emergence of cannibalism-avoidance behaviour depends strongly on assumptions about parasite-based mortality rates. Third, our literature review indicated that parasite species potentially able to follow a carnivore–carnivore indirect cycle, as well as those transmitted via meat consumption, are rare in our study system. Our findings support the existence of a novel coevolutionary relation between carnivores and their parasites, and suggest that carnivore and herbivore carcasses play very different roles in food webs and ecosystems., Dirección General del Medio Natural (Murcia Region), Sierra Espuña Regional Park and Sierras de Cazorla, Segura y Las Villas Natural Park provided with logistics, permissions and financial support. M.M. acknowledges financial support through the Severo Ochoa Program for Centres of Excellence in R+D+I (SEV‐2012‐0262) and by a research contract Ramón y Cajal from the MINECO (RYC‐2015‐19231). This study was partly funded by the Spanish Ministry of Economy and Competitiveness and EU ERDF funds through projects CGL2006‐10689/BOS, CGL2009‐12753‐C02‐02, CGL2012‐40013‐C02‐01/02 and CGL2015‐66966‐C2‐1‐2‐R. A. Kane and one anonymous reviewer improved the first version of the manuscript.