Estefanía Micó

Saproxylic beetles (Coleoptera) and hoverflies (Diptera: Syrphidae) from a Mediterranean forest: towards a better understanding of their biology for species conservation

This report represents the first integrative study on saproxylic Coleoptera and Diptera Syrphidae from a representative Mediterranean forest in Cabañeros National Park in Central Spain. We collected 107 beetles, representing 32 families, and 25 species of hoverfly. Two undescribed and numerous rare beetle species were recorded, as were four hoverflies considered to be threatened species in Europe. We compiled biological information for all of the taxa encountered and recorded new data on their feeding habits, breeding microsites, and known tree associations. We found that the saproxylic biodiversity in this National Park was characterized by a significant number of Central European and North African species. Our results on the saproxylic assemblage, comprising many rare and poorly known species, of a typical Mediterranean forest represent a first step toward improved understanding of the saproxylic community and establishing the basis for conservation strategies in this region.

Larval morphology enhances phylogenetic reconstruction in Cetoniidae (Coleoptera: Scarabaeoidea) and allows the interpretation of the evolution of larval feeding habits

Abstract The Cetoniidae, the showiest of scarabs, comprises some 3900 species in 515 genera, distributed worldwide except for subpolar areas and some offshore New Zealand islands. Parsimony analysis of 76 larval and adult characters and 42 terminal taxa supports the monophyly of Cetoniidae (sensu Krikken, 1984 ), but not of the traditionally considered subfamilies Cetoniinae and Trichiinae (sensu Krikken, 1984 ). In the study taxon, larval characters are shown to be more informative than those of adults for deeper phylogeny. The evolution of some larval characters (head and legs) in relation to feeding habits is discussed on the basis of phylogenetic analysis. The results show an evolutionary shift from wood associations to a higher ecological plasticity that allows the larvae to feed on wide sources of organic matter (including compost, dung, gopher burrows, packrat middens, ant debris piles, etc.).

Breaking down Complex Saproxylic Communities: Understanding Sub-Networks Structure and Implications to Network Robustness

Saproxylic insect communities inhabiting tree hollow microhabitats correspond with large food webs which simultaneously are constituted by multiple types of plant-animal and animal-animal interactions, according to the use of trophic resources (wood- and insect-dependent sub-networks), or to trophic habits or interaction types (xylophagous, saprophagous, xylomycetophagous, predators and commensals). We quantitatively assessed which properties of specialised networks were present in a complex networks involving different interacting types such as saproxylic community, and how they can be organised in trophic food webs. The architecture, interacting patterns and food web composition were evaluated along sub-networks, analysing their implications to network robustness from random and directed extinction simulations. A structure of large and cohesive modules with weakly connected nodes was observed throughout saproxylic sub-networks, composing the main food webs constituting this community. Insect-dependent sub-networks were more modular than wood-dependent sub-networks. Wood-dependent sub-networks presented higher species degree, connectance, links, linkage density, interaction strength, and were less specialised and more aggregated than insect-dependent sub-networks. These attributes defined high network robustness in wood-dependent sub-networks. Finally, our results emphasise the relevance of modularity, differences among interacting types and interrelations among them in modelling the structure of saproxylic communities and in determining their stability.

Action of the saproxylic scarab larva Cetonia aurataeformis (Coleoptera: Scarabaeoidea: Cetoniidae) on woody substrates

The saproxylic beetle Cetonia aurataeformis Curti (Scarabaeoidea: Cetoniidae) is a common Iberian species, whose larvae develop in tree cavities feeding on wood and litter. The aim of this paper is to analyse how the larvae of this cetonid modify the woody substrate by feeding and what the ecological implications on their microhabitat could be. Thermal analysis and infrared spectroscopy have been used to study the changes suffered by different substrates, litter and wood of Betula alba and Quercus pyrenaica, after digestion by the larvae. Results show that larvae of C. aurataeformis are able to digest polysaccharides and lignin producing a residue richer in nutrients than the original substrate and with an organic structure that contains a fraction of lignin that is easier to decompose. The main conclusion is that the action of cetonid larvae on woody substrates could facilitate their use by other saproxylic organisms in natural ecosystems.

The “dehesa”, a key ecosystem in maintaining the diversity of Mediterranean saproxylic insects (Coleoptera and Diptera: Syrphidae)

The “dehesa” is a traditional Iberian agrosilvopastoral ecosystem characterized by the presence of old scattered trees that are considered as “keystone-structures”, which favor the presence of a wide range of biodiversity. We show the high diversity of saproxylic beetles and syrphids (Diptera) in this ecosystem, including red-listed species. We analyzed whether saproxylic species distribution in the “dehesa” was affected by tree density per hectare, dominant tree species or vegetation coverage. Species diversity did not correlate with tree density; however, it was affected by tree species and shrub coverage but in a different way for each taxon. The highest beetle diversity was linked to Quercus pyrenaica, the most managed tree species, with eight indicator species. In contrast, Q. rotundifolia hosted more species of saproxylic syrphids. Regarding vegetation coverage, shrub coverage was the only variable that affected insect richness, again in a different way for both taxa. In contrast, beetle species composition was only affected by dominant tree species whereas syrphid species composition was not affected by tree species or shrub coverage. We concluded that the high diversity of saproxylic insects in the “dehesa” is related to its long history of agrosilvopastoral management, which has generated landscape heterogeneity and preserved old mature trees. However, the richness and composition of different taxa of insects respond in different ways to tree species and vegetation coverage. Consequently, conservation strategies should try to maintain traditional management, and different saproxylic taxa should be used to monitor the effect of management on saproxylic diversity.

New Larval Descriptions and Biology of Some New World Anomalini Beetles (Scarabaeidae: Rutelinae)

Abstract The third-instar larvae of four Anomala species: A. cincta Say, A. forreri Bates, A. sticticoptera Blanchard, and A. discoidalis Bates from Mexico are described and diagnostic characters of the species are illustrated. The third-instar of two Callistethus species: C. vidua (Newman) and C. cupricollis (Blanchard) from Mexico are also described and illustrated. The pupa of A. cincta is described. These six species are included in a key to the larvae of North American and Mexican Anomalini, which now includes four genera and 20 species. The use of larval morphology in the taxonomy of Anomalini is briefly discussed. Data on larval biology and life cycle of the six species are also provided.

Roles of endothermy in niche differentiation for ball‐rolling dung beetles (Coleoptera: Scarabaeidae) along an altitudinal gradient

Abstract 1. An analysis of whether niche differentiation in ball‐rolling dung beetles can be explained by the way in which they regulate their body temperature was conducted.

What can physical, biotic and chemical features of a tree hollow tell us about their associated diversity?

Abstract Tree hollows are keystone structures for saproxylic fauna and host numerous endangered species. However, not all tree hollows are equal. Many variables including physical, biotic and chemical ones, can characterise a tree hollow, however, the information that these could provide about the saproxylic diversity they harbour has been poorly explored. We studied the beetle assemblages of 111 Quercus species tree hollows in four protected areas of the Iberian Peninsula. Three physical variables related to tree hollow structure, and two biotic ones (presence of Cetoniidae and Cerambyx species recognised as ecosystem engineers) were measured in each hollow to explore their relative effect on beetle assemblages. Moreover, we analysed the chemical composition of the wood mould in 34 of the hollows, in order to relate beetle diversity with hollow quality. All the environmental variables analysed (physical and biological) showed a significant influence on saproxylic beetle assemblages that varied depending on the species. Furthermore, the presence of ecosystem engineers affected both physical and chemical features. Although wood mould volume, and both biotic variables could act as beetle diversity surrogate, we enhance the presence of Cetoniidae and Cerambyx activity (both easily observable in the field) as indicator variables, even more if both co-occur as each affect to different assemblages. Finally, assimilable carbon and phosphorous contents could act as indicator for past and present beetle activity inside the cavity that could become a useful tool in functional diversity studies. However, an extension of this work to other taxonomic groups would be desirable.

Influence of tree hollow characteristics on the diversity of saproxylic insect guilds in Iberian Mediterranean woodlands

Saproxylic diversity assessment is a major goal for conservation strategies in woodlands and it should consider woodland composition and configuration at site and tree level as key modelling factors. However, in Mediterranean woodlands little is known about the relation with the environmental factors that structure their assemblages, especially those linked to tree hollow microhabitats. We assessed the diversity of Syrphidae (Diptera) and Coleoptera saproxylic guilds that co-occurred in tree hollows located in three different Iberian Mediterranean woodlands in the Cabañeros National Park (Spain). Furthermore, we evaluated how differences in tree hollow microenvironmental variables (understood as the physical and biotic characteristics of a hollow and tree individual) influenced saproxylic guild diversity both within and among woodland sites. We found that woodland sites that provided greater heterogeneity of trees and hollow microhabitats determined higher saproxylic guild diversity. Nevertheless, certain species or even complete guilds can be favoured in woodlands where some hollow microhabitats predominate as a consequence of historical tree management. In general, hollow volume was the main determining factor for saproxylic guild richness and abundance in woodland sites, and large hollow volume was usually related to higher diversity, which highlighted the importance of multi-habitat hollow trees. Moreover, saproxylic guilds also responded to other different microenvironmental variables, which indicated different ecological preferences among guilds. The conservation of saproxylic insects in Iberian Mediterranean areas must be addressed to protect woodland sites that provide high diversity and large numbers of tree hollow microhabitats, and practices to enhance microhabitat heterogeneity should even be encouraged.

Facilitation among Saproxylic Insects Inhabiting Tree Hollows in a Mediterranean Forest: The Case of Cetonids (Coleoptera: Cetoniidae) and Syrphids (Diptera: Syrphidae)

ABSTRACT Tree hollows offer an ideal niche for saproxylic insects in mature Mediterranean forests, where Diptera and Coleoptera are the richest groups. Co-occurrence is frequently observed among many species of both groups in these microhabitats, and some of these species have been considered to facilitate the presence of other species by acting as ecosystem engineers. One of the systems that is found in Mediterranean tree hollows is formed by cetonid (Coleoptera: Cetoniidae) and syrphid (Diptera: Syrphidae) larvae. Here, cetonid larvae feed on wood and litter and produce a substrate that is easier to decompose. To assess the possible role of these larvae as facilitating agents for the saproxylic guild, we studied whether the presence of saprophagous Syrphidae inside tree hollows is associated with the activity of cetonid larvae. Furthermore, in laboratory conditions, we tested whether cetonid larvae activity can improve the development and fitness of the saprophagous syrphid species. Our results show that “cetonid activity” was the variable that best explained the presence of saprophagous syrphid species in natural conditions. Myathropa florea (L., 1758) was one of the species most influenced by this activity. The laboratory experiment gave similar results, demonstrating that an enriched substrate with Cetonia aurataeformis Curti, 1913 larval feces improves syrphid larval growth rate and fitness of adults (measured as longer wing length) of M. florea.