Contrasting effects of land‐use changes on herbivory and pollination networks

Abstract

Land‐use changes, one of the greatest threats to global biodiversity, can cause underappreciated effects on ecosystems by altering the structures of interspecific interaction networks. These effects have typically been explored by evaluating interaction networks composed of a single type of interaction. Therefore, it remains unclear whether the different types of interaction networks sharing the same species respond to the same land‐use changes in a similar manner.To compare the responses of herbivory and pollination networks to land‐use changes, we investigated both types of interaction networks in seminatural grasslands categorized into three types of agricultural land‐use (abandoned, extensively managed, and intensively managed) in a Japanese agricultural landscape. We quantified the structures of the interaction networks using several indices (connectance, evenness, diversity, generality, network specialization, and robustness) and compared them among different land‐use types. We conducted piecewise SEM to differentiate the direct and indirect effects of land‐use changes on the network structures.Although both land‐use changes (abandonment and intensification) led to reduced plant and insect species richness, the structures of herbivory and pollination networks showed different responses to the land‐use changes. There was a marked contrast in network generality; while, herbivore species were less generalized (i.e., having fewer host plant species) in fields with land‐use intensification, pollinator species were less generalized in abandoned fields.Furthermore, the mechanisms behind the changes in interaction networks were also different between pollination and herbivory networks. The change in herbivory network generality was induced by the decrease in plant species richness, whereas the change in pollination network generality was mainly induced by the effect independent of changes in species richness and composition, which possibly reflect the less number of flowers in shaded environment.The present study demonstrates that agricultural land‐use changes affect herbivory and pollination networks in contrasting ways and suggests the importance of assessing multiple types of interaction networks for biodiversity conservation in plant–insect systems. Our results also highlight the underappreciated importance of maintaining habitats with an intermediate intensity of land‐use.

Why species richness of plants and herbivorous insects do or do not correlate

“…Therefore, in light of the unutilized plant species hypothesis, we may explain the varying correlation between plant and insect diversities among previous studies by examining such factors. Second, previous studies have suggested that the proportion of generalist insects varies among study systems that differ in time after disturbance (Piechnik, Lawler, & Martinez, 2008), degree of land‐use intensification (de Araújo, Vieira, Lewinsohn, & Almeida‐Neto, 2015; Shinohara, Uchida, & Yoshida, 2019), spatial scale (Hughes, 2000) and taxonomic groups (Forister et al, 2015). Therefore, incorporating these factors into future studies would help explain the relationship between plant and insect species richness.…”

“…We showed that the correlation between plant and herbivorous insect species richness was negatively affected by insect generality, which indicates that the possibility of colonization of specialist insect species was enhanced with increasing plant species richness, whereas generalist insect species occurred irrespective of plant species richness. It has been suggested that insect generality may vary among study systems that differ in time after disturbance (Piechnik et al 2008), degree of land-use intensification (de Araujo et al 2015, Shinohara et al 2019, spatial scale (Hughes 2000), and taxonomical groups (Forister et al 2015). Therefore, incorporating those factors in future studies may help explain the relationship between plant-insect species richness.…”

Why species richness of plants and herbivorous insects do or do not correlate

“…We showed that the correlation between plant and herbivorous insect species richness was negatively affected by insect generality, which indicates that the possibility of colonization of specialist insect species was enhanced with increasing plant species richness, whereas generalist insect species occurred irrespective of plant species richness. It has been suggested that insect generality may vary among study systems that differ in time after disturbance (Piechnik et al 2008), degree of land-use intensification (de Araujo et al 2015, Shinohara et al 2019), spatial scale (Hughes 2000), and taxonomical groups (Forister et al 2015). Therefore, incorporating those factors in future studies may help explain the relationship between plant–insect species richness.…”

A perspective on stage‐structured mutualism and its community consequences

“…herbivory and pollination) in hybrid network communities. However, the role of stage structure has been largely ignored in community network studies (Melián et al 2009, Allesina and Tang 2012, Bascompte and Jordano 2014, Suweis et al 2014, Shinohara et al 2019, Valdovinos 2019. Systematic measurements of structural properties (e.g.…”