Plant composition, not richness, drives occurrence of specialist herbivores

Abstract

1. How herbivore plant diversity relationships are shaped by the interplay of biotic and abiotic environmental variables is only partly understood. For instance, plant diversity is commonly assumed to determine abundance and richness of associated specialist herbivores. However, this relationship can be altered when environmental variables such as temperature covary with plant diversity. 2. Using gall‐inducing arthropods as focal organisms, biotic and abiotic environmental variables were tested for their relevance to specialist herbivores and their relationship to host plants. In particular, the hypothesis that abundance and richness of gall‐inducing arthropods increase with plant richness was addressed. Additionally, the study asked whether communities of gall‐inducing arthropods match the communities of their host plants. 3. Neither abundance nor species richness of gall‐inducing arthropods was correlated with plant richness or any other of the tested environmental variables. Instead, the number of gall species found per plant decreased with plant richness. This indicates that processes of associational resistance may explain the specialised plant herbivore relationship in our study. 4. Community composition of gall‐inducing arthropods matched host plant communities. In specialised plant herbivore relationships, the presence of obligate host plant species is a prerequisite for the occurrence of its herbivores. 5. It is concluded that the abiotic environment may only play an indirect role in shaping specialist herbivore communities. Instead, the occurrence of specialist herbivore communities might be best explained by plant species composition. Thus, plant species identity should be considered when aiming to understand the processes that shape diversity patterns of specialist herbivores.

Fire affects galling insect communities through vegetation changes in a subtropical seasonally semiarid forest

“…Some studies have considered only the host plant richness and a linear positive relationship between host plant and galling insect richness was also found (Araújo, 2011;Souza et al, 2016). Moreover, in agreement with the high specificity of galling insects to their host plants (Carneiro et al, 2009), the specific composition of these insect communities has been closely related to floristic composition (Julião et al, 2017;Knuff et al, 2019). The proportion of plants damaged by phytophagous insects was also used as an herbivory indicator (Ekholm et al, 2019;Faeth & Simberloff, 1981) and showed changes in disturbed habitats (Altamirano et al, 2016).…”

“…In general, the studies assessing insect galling richness do not incorporate floristic composition, which may play an important role in shaping galling insect richness (Coelho et al, 2017(Coelho et al, , 2018Souza et al, 2016;Veldtman & McGeoch, 2003). For instance, the presence of the most frequently attacked plant life form by galling insect may modulate galling insect richness (Cuevas-Reyes et al, 2014;Gonçalves-Alvim & Fernandes, 2001;Knuff et al, 2019;Melo Júnior et al, 2019).…”

Evaluating the effectiveness of retention forestry to enhance biodiversity in production forests of Central Europe using an interdisciplinary, multi‐scale approach

“…Box 1 (Continued) (Knuff, Staab, Frey, Helbach, & Klein 2019). Based on meta-analyses, ConFoBi researchers confirmed that crown-damaged trees improve nesting opportunities for cavity-nesting birds (Gutzat & Dormann, 2018) and that woodpeckers select cavitiesby relative rather than absolute tree size (Basile, Mikusinski, & Storch, 2020), but found that bird guilds are affected differently by forestry measures including retention, according to their life history, biome, and forest type .…”

“…Preliminary results indicate positive overall effects of retention of structural elements for forest biodiversity but also high variability among taxa and landscape settings; further, our findings suggest high potential for optimizing the integration of retention into management practice. The first ConFoBi publications described technical and methodological advances for quantifying forest structures; for example, we found a high potential for optimizing the quality in reconstruction of 3D forest models from aerial images based on drones (Frey, Kovach, Stemmler, & Koch, ), showed how the abundance and diversity of tree‐related microhabitats can be predicted with readily available forest attributes (Asbeck, Pyttel, Frey, & Bauhus, ), recorded a lichen species new for Germany (Wirth, Tønsberg, Reif, & Stevenson, ), optimized the trap design to capture flying arthropods (Knuff, Winiger, Klein, Segelbacher, & Staab, ), and showed that the occurrence of specialist herbivore communities might be best explained by plant species composition rather than the abiotic environment (Knuff, Staab, Frey, Helbach, & Klein, ). Based on meta‐analyses, ConFoBi researchers confirmed that crown‐damaged trees improve nesting opportunities for cavity‐nesting birds (Gutzat & Dormann, ) and that woodpeckers select cavitiesby relative rather than absolute tree size (Basile, Mikusinski, & Storch, ), but found that bird guilds are affected differently by forestry measures including retention, according to their life history, biome, and forest type (Basile, Mikusinski, & Storch, ).…”

Bottom‐up and top‐down forces in plant‐gall relationships: testing the hypotheses of resource concentration, associational resistance, and host fitness reduction

“…Non-host stems and leaves can represent a physical barrier between the insect and the host (Perrin, 1976;Risch, 1981) and can disrupt visual cues and the background, reducing the probability that the galling insect will find its host (Castagneyrol et al, 2014;Muiruri et al, 2019). Although studies have demonstrated associations between plant diversity and gall abundance (Grossman et al, 2019;Knuff et al, 2019), the role of non-host tree abundance is still unclear in natural systems. As galling insects are very small insects, their flight is probably wind dependent (Jermy et al, 1988;Withers & Harris, 1997) and the physical disturbance of non-host individuals could have a strong impact on gall distribution regardless of species diversity.…”