No abstract

The identities of most arthropod associates of cynipid-induced oak galls in the western Palearctic are generally known. However, a comprehensive accounting of associates has been performed for only a small number of the galls induced by the estimated 700 species of cynipid gall wasp in the Nearctic. This gap in knowledge stymies many potential studies of diversity, coevolution, and community ecology, for which oak gall systems are otherwise ideal models. We report rearing records of insects and other arthropods from more than 527,306 individual galls representing 201 different oak gall types collected from 32 oak tree species in North America. Of the 201 gall types collected, 155 produced one or more animals. A total of 151,075 animals were found in association with these 155 gall types, and of these 61,044 (40.4%) were gall wasps while 90,031 (59.6%) were other arthropods. We identified all animals to superfamily, family, or, where possible, to genus. We provide raw numbers and summaries of collections, alongside notes on natural history, ecology, and previously published associations for each taxon. For eight common gall-associated genera (Synergus, Ceroptres, Euceroptres, Ormyrus, Torymus, Eurytoma, Sycophila, and Euderus), we also connect rearing records to gall wasp phylogeny, geography, and ecology - including host tree and gall location (host organ), and their co-occurrence with other insect genera. Though the diversity of gall wasps and the large size of these communities is such that many Nearctic oak gall-associated insects still remain undescribed, this large collection and identification effort should facilitate the testing of new and varied ecological and evolutionary hypotheses in Nearctic oak galls.

Premise of the Study Phenological mismatch has received attention in plant–pollinator interactions, but less so in seed dispersal mutualisms. We investigated whether the seasonal availability of myrmecochorous seeds is well matched to the seasonal activity patterns of seed‐dispersing ants. Methods We compared seasonal timing of seed removal by a keystone seed‐dispersing ant, Aphaenogaster rudis, and fruit dehiscence of several species of plants whose seeds it disperses in a deciduous forest in southern Ontario, Canada. We examined the timing of elaiosome “robbing” by the nonnative slug Arion subfuscus and tested whether seed removal by ants declines in response to supplementation with additional elaiosome‐bearing seeds (ant “satiation”). Key Results Seed removal from experimental depots peaked early in the season for all plant species and correlated with temperature. In contrast, elaiosome robbing by slugs increased late in the season and thus may disproportionately affect plants with late‐dehiscing fruits. Ant colonies removed seeds at similar rates regardless of seed supplementation, indicating that satiation likely does not impact seasonal patterns of seed dispersal in this system. Fruits of the five myrmecochorous plant species in our study dehisced at discrete intervals throughout the season, with minimal overlap among species. Peak dehiscence did not overlap with peak seed removal for any plant species. Conclusions Fruit dehiscence of myrmecochorous plants and peak ant seed dispersal activity occur asynchronously. Whether future climate warming will shift ant and plant phenologies in ways that have consequences for seed dispersal remains an open question.

1. In generalized mutualisms, species vary in the quality of services they provide to their partners directly via traits that affect partner fitness and indirectly via traits that influence interactions among mutualist species that play similar functional roles. Myrmecochory, or seed dispersal by ants, is a generalized mutualism with ant species varying in the quality of dispersal services they provide to their plant partners. Variation in ant species identity can directly impact seed dispersal patterns and plant community composition; however, we know less about how interactions among seed-dispersing ant species indirectly influence plant partners. 2. The invasive ant Myrmica rubra, is a high-quality seed-disperser in its native range that interacts with myrmecochores (ant-dispersed plants) and the high-quality seed disperser Aphaenogaster sp. in its invaded range. We use this system to examine how interactions between two functionally similar mutualist ant species influence the recruitment and community composition of ant-dispersed plants. 3. We performed a field mesocosm experiment and a laboratory behavioural experiment to compare discovery and dominance behaviours between ant species, and seed dispersal and seedling recruitment of four myrmecochore species among intraspecific interaction treatments of each ant species and an interspecific interaction treatment. 4. We found that M. rubra was better at discovering and dispersing seeds, but Aphaenogaster sp. was dominantly aggressive over M. rubra. Interspecific interactions dampened seed dispersal relative to dispersal by the better disperser. Despite this dampening, we found no effect of interspecific interactions on seedling recruitment. However, community composition of seedlings in the interspecific interaction treatment was more similar to composition in the aggressively dominant ant (Aphaenogaster sp.) treatment than in the better discoverer ant M. rubra treatment. 5. We show that interspecific interactions between mutualist species in the same functional guild affect the outcome of mutualistic interactions with partner species. Despite the native ant dispersing fewer seeds, its dominance over the subordinate (invasive) ant has the potential to allow for some level of biotic resistance against the effects of M. rubra on plant communities when these species coexist.