Diversity and specificity of host‐natural enemy interactions in an urban‐rural interface

Abstract

1. Urbanisation and agricultural intensification cause the replacement of natural ecosystems but might also create novel habitats in urban and rural ecosystems promoting some insect communities by providing food and nesting resources.2. This study investigated how host-natural enemy communities change in urban and rural landscapes and their transitional zone, the urban-rural interface, by using trap nests for cavity-nesting Hymenoptera in gardens and rapeseed fields that were either isolated or paired in the urban-rural interface.3. Host dynamics were important for natural enemy occurrence, species richness and parasitism rates, and landscape effects were evident for natural enemy variables except for the richness of bee natural enemies. The number of parasitised brood cells was at its highest in the urban-rural interface, but the highest parasitism rates of bees were observed in isolated gardens. Parasitism rates of bees were negatively affected by host abundance, while parasitism rates of wasps were positively affected.4. Higher specialisation and lower connectivity of host-natural enemy interactions were found in paired habitats than in isolated habitats. This indicates that paired habitats comprise more specific natural enemies and vulnerable interactions, while isolated habitats comprise more generalist natural enemies, and thus interactions appear more stable.5. These results confirm that host dynamics play an essential role in the abundance and richness of natural enemies and drive parasitism. However, high habitat heterogeneity found in the urban-rural interface can also have an effect on host-natural enemy communities. This highlights that the provisioning of resources in the urban-rural interface can benefit insect communities in these areas.

Does urbanization explain differences in interactions between an insect herbivore and its natural enemies and mutualists?

“…Urbanized environments might affect organisms at higher trophic levels more than their hosts or prey, particularly when they exhibit higher levels of resource specialization (Tscharntke et al 1998;Bailey et al 2005;Pereira-Peixoto et al 2016). In our study system, this may apply to insect predators but does not appear to affect the likelihood of colonies suffering parasitoid attack.…”

“…Urbanization is arguably the greatest anthropogenic transformation that ecological systems experience, and while most studies of urban ecology focus on changes to the diversity and abundance of species inhabiting towns and cities, attention has only started to focus on how assemblages of interacting species are formed in urban areas, and how this is affected by the intensity of urbanization (Bennett and Gratton 2012;Quispe and Fenoglio 2015;Pereira-Peixoto et al 2016;Turrini et al 2016). Fragmentation reduces populations of native plants (Benitez-Malvido 1998;Jules 1998;Williams et al 2005), leads to decreased connectivity between vegetation patches and existing patches tend to be smaller (Medley et al 1995;McKinney 2002) and therefore of reduced quality as habitat for many animal species (Bradley and Altizer 2007;Faeth et al 2011;Turrini et al 2016).…”

“…Few studies have considered how these changes influences the outcome of ecological interactions at multiple trophic levels (Shrewsbury and Raupp 2006;Bennett and Gratton 2012;Fenoglio et al 2013;Pereira-Peixoto et al 2016;Turrini et al 2016). For example, abiotic environmental factors might interfere with biotic interactions, thereby modulating the strength of the trophic effects on food webs (Ritchie 2000;Preisser and Strong 2004;Turrini et al 2016).…”

Trap nests for bees and wasps to analyse trophic interactions in changing environments—A systematic overview and user guide

“…While generalist parasitoids, such as Melittobia spp. are sometimes present (e.g., Pereira‐Peixoto, Pufal, Staab, Martins, & Klein, ; Tylianakis et al., ), most parasitoids are host‐specific and only attack a single or a few closely related species at a given locality (e.g., Orlovskyte et al., ; Staab et al., ). In addition to the trophic interactions with pollen, prey and parasitoids, less well‐known interaction types were also studied with trap nests, including the plant species that leaf‐cutting bees exploit for nest construction (e.g., Torretta, Durante, Colombo, & Mabel Basilio, ) or the oil sources of neotropical oil‐collecting bees (e.g., Carvalho, Carreira, Rego, & Albuquerque, ).…”

The presence of high numbers of empty shells in anthropogenic habitats is insufficient to attract shell adopters among the insects

“…The lower abundance and species richness of insects in anthropogenic habitats were reported repeatedly from many insect assemblages (Pereira et al ., ; Cardinale, ; Geslin et al ., ; Pereira‐Peixoto et al ., ), but the observations of reverse relationships are also known, particularly in a broad range of disturbance dependent species including, for example, various aculeate Hymenoptera (Cizek et al ., ; Tropek et al ., ; Heneberg et al ., ; Bogusch et al ., ). Here, we have shown that despite most of the dominant empty snail shell adopters among insects managed to colonise the anthropogenic habitats, they failed to establish there as large populations as in the natural habitats.…”