Plant reproductive traits mediate tritrophic feedback effects within an obligate brood-site pollination mutualism.

Plants, herbivores and parasitoids affect each other directly and indirectly; however, feedback effects mediated by host plant traits have rarely been demonstrated in these tritrophic interactions. Brood-site pollination mutualisms (e.g. those involving figs and fig wasps) represent specialised tritrophic communities where the progeny of mutualistic pollinators and of non-mutualistic gallers (both herbivores) together with that of their parasitoids develop within enclosed inflorescences called syconia (hence termed brood-sites or microcosms). Plant reproductive phenology (which affects temporal brood-site availability) and inflorescence size (representing brood-site size) are plant traits that could affect reproductive resources, and hence relationships between trees, pollinators and non-pollinating wasps. Analysing wasp and seed contents of syconia, we examined direct, indirect, trophic and non-trophic relationships within the interaction web of the fig-fig wasp community of Ficus racemosa in the context of brood site size and availability. We demonstrate that in addition to direct resource competition and predator-prey (host-parasitoid) interactions, these communities display exploitative or apparent competition and trait-mediated indirect interactions. Inflorescence size and plant reproductive phenology impacted plant-herbivore and plant-parasitoid associations. These plant traits also influenced herbivore-herbivore and herbivore-parasitoid relationships via indirect effects. Most importantly, we found a reciprocal effect between within-tree reproductive asynchrony and fig wasp progeny abundances per syconium that drives a positive feedback cycle within the system. The impact of a multitrophic feedback cycle within a community built around a mutualistic core highlights the need for a holistic view of plant-herbivore-parasitoid interactions in the community ecology of mutualisms.

Vertical canopy gradient shaping the stratification of leaf-chewer-parasitoid interactions in a temperate forest.

Knowledge about herbivores and their parasitoids in forest canopies remains limited, despite their diversity and ecological importance. Thus, it is important to understand the factors that shape the herbivore-parasitoid community structure, particularly the effect of vertical gradient. We investigated a quantitative community dataset of exposed and semiconcealed leaf-chewing larvae and their parasitoids along a vertical canopy gradient in a temperate forest. We sampled target insects using an elevated work platform in a 0.2 ha broadleaf deciduous forest plot in the Czech Republic. We analyzed the effect of vertical position among three canopy levels (first [lowest], second [middle], and third [highest]) and tree species on community descriptors (density, diversity, and parasitism rate) and food web structure. We also analyzed vertical patterns in density and parasitism rate between exposed and semiconcealed hosts, and the vertical preference of the most abundant parasitoid taxa in relation to their host specificity. Tree species was an important determinant of all community descriptors and food web structure. Insect density and diversity varied with the vertical gradient, but was only significant for hosts. Both host guilds were most abundant in the second level, but only the density of exposed hosts declined in the third level. Parasitism rate decreased from the first to third level. The overall parasitism rate did not differ between guilds, but semiconcealed hosts suffered lower parasitism in the third level. Less host-specific taxa (Ichneumonidae, Braconidae) operated more frequently lower in the canopy, whereas more host-specific Tachinidae followed their host distribution. The most host-specific Chalcidoidea preferred the third level. Vertical stratification of insect density, diversity, and parasitism rate was most pronounced in the tallest tree species. Therefore, our study contradicts the general paradigm of weak arthropod stratification in temperate forest canopies. However, in the network structure, vertical variation might be superseded by variation among tree species.

Species richness and parasitism in a fragmented landscape: experiments and field studies with insects on Vicia sepium.

Effects of habitat fragmentation on species diversity and herbivore-parasitoid interactions were analyzed using the insect community of seed feeders and their parasitoids in the pods of the bush vetch (Vicia sepium L.). Field studies were carried out on 18 old meadows differing in area and isolation. The area of these meadows was found to be the major determinant of species diversity and population abundance of endophagous insects. Effects of isolation were further analyzed experimentally using 16 small plots with potted vetch plants isolated by 100-500 m from vetch populations on large old meadows. The results showed that colonization success greatly decreased with increasing isolation. In both cases, insect species were not equally affected. Parasitoids suffered more from habitat loss and isolation than their phytophagous hosts. Minimum area requirements, calculated from logistic regressions, were higher for parasitoids than for herbivores. In addition, percent parasitism of the herbivores significantly decreased with area loss and increasing isolation of Vicia sepium plots, supporting the trophic-level hypothesis of island biogeography. Species with high rates of absence on meadows and isolated plant plots were not only characterized by their high trophic level, but also by low abundance and high spatial population variability. Thus conservation of large and less isolated habitat remnants enhances species diversity and parasitism of potential pest insects, i.e., the stability of ecosystem functions.

Piper kelleyi, a hotspot of ecological interactions and a new species from Ecuador and Peru.

We describe Piper kelleyi sp. nov., a new species from the eastern Andes of Ecuador and Peru, named in honor of Dr. Walter Almond Kelley. Piper kelleyi is a member of the Macrostachys clade of the genus Piper and supports a rich community of generalist and specialist herbivores, their predators and parasitoids, as well as commensalistic earwigs, and mutualistic ants. This new species was recognized as part of an ecological study of phytochemically mediated relationships between plants, herbivores, predators, and parasitoids. Compared to over 100 other Piper species surveyed, Piper kelleyi supports the largest community of specialist herbivores and parasitoids observed to date.

ResumenDescribimos la nueva especie Piper kelleyisp. nov., proveniente de la vertiente Este de los Andes en el Ecuador y Perú, y nombrada en honor al Dr. Walter Almond Kelley. Piper kelleyi forma parte del clado Macrostachys del género Piper y conforma la base alimenticia de una diversa comunidad de herbívoros, tanto generalistas como especialistas, depredadores y parasitoides de estos herbívoros, así como tijeretas comensales y hormigas mutualistas. Esta nueva especie fue reconocida como parte de una investigación ecológica de las interacciones, mediadas por fitoquímica, entre plantas, herbívoros, depredadores y parasitoides. En comparación con más de otras 100 especies de Piper estudiadas, Piper kelleyi hospeda la comunidad de insectos con mayor diversidad de herbívoros especialistas y parasitoides observada hasta ahora.