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Disentangling the coexistence strategies of mud-daubing wasp species through trophic analysis in oases of Baja California peninsula

Citation

Falcón-Brindis, Armando; Rodríguez-Estrella, Ricardo; Jiménez, María Luisa (2019), Disentangling the coexistence strategies of mud-daubing wasp species through trophic analysis in oases of Baja California peninsula, Dryad, Dataset, https://doi.org/10.5061/dryad.5x69p8d09

Abstract

Species within the same trophic level show different strategies to avoid competition. Among these mechanisms, differences in body size, spatio-temporal segregation, and diet preference often leads to a niche partitioning. Nonetheless, little attention on coexisting predatory insects and their network interactions has been paid. In this study, we analyzed the strategies to avoid competition among three sympatric mud-daubing wasps of the genus Trypoxylon (Hymenoptera: Crabronidae) in oases and their surrounding xeric area from the Baja California peninsula, Mexico. We compared the prey richness, composition and proportion of spider guilds that were captured by the wasps. We tested whether the differences in wasp body size explained the niche breadth, niche overlap and the size of spider prey. We assessed the spider-wasp interactions through a network analysis. With the use of trap-nests, we collected 52 spider species captured by the wasps. Both the guild and species composition of preyed spiders was different between the three wasp species. Differential proportions in the capture of spider guilds and a little diet overlap were found among the wasp species. We found that the wasp body size was positively correlated with prey size, but it was not a proxy of niche breadth. Moreover, the largest wasp species was able to nest in both mesic and xeric habitats, while the two smaller species were restricted to the oases. This study reveals that the diversity of spiders in oases of Baja California peninsula is crucial to maintain highly specialized oasis-dependent wasp species. The niche partitioning between mud-daubing wasps can be shaped by their inherent body size limitations and hunting strategies through foraging specialization for specific spider guilds. Food selection and slight differences in body size reduce competition and allow the coexistence of sympatric wasps. Our study is the first approach exploring the interaction networks between mud-daubing wasps and their spider preys, highlighting new insights into the morphological and ecological factors that shape antagonistic interactions, and allow the coexistence of predators in deserts.

Methods

We used artificial cavities to collect the wasp´s nests and identify their composition (i.e. spider prey). We set the traps in both the oases and the surrounding desert to evaluate the prey composition between habitats. The traps were set in gradual distances from the edge of the waterbody (inside the oasis) towards the desert area. That is, from around 5.0 m to 3,500 m away from the waterbody. From April to September 2016 we sampled the southernmost oases: Santiago (SA), El Pilar (EP), and La Purísima (LP). From April to September 2017, the northernmost oases were sampled: El Sauzal (ES), San Borja (SB), and San Fernando (SF). In both years, we monthly replaced the occupied traps. 

In order to determine the relative level of dietary specialization and niche segregation of the species, the niche breadth and niche overlap were calculated for the three Trypoxylon wasps. Hurlbert's formula was applied to obtain the standardized niche breadth (Bj). We used the Pianka´s index to measure niche overlap. Niche breadth index ranges from 0 to 1, where values close to 1 indicate more specialization. Pianka´s index also ranges from 0 to 1, where values close to 1 indicate a higher diet overlap. We used the spaa package to compute these indexes. We built a bipartite network (predator-prey) to calculate the complementary specialization index (H2´) and Shannon diversity of interactions between both trophic groups. H2´ index ranges between 0 (no specialization) and 1 (complete specialization). Since this index can be sensitive to matrices constructed with few species, we compared our data against 1000 random null models that avoid biases regardless the matrix size. With the null model approach, we assessed that the spider-wasp interactions are not being reflections of the sampling properties, thus producing random links between predator and prey. The network analysis was done with the package bipartite in R.

To test whether the size of predators influenced the niche breadth and prey size selection, we measured morphological attributes of size on both wasps and spiders. We obtained the values of body length, facial and intertegular distance from the three Trypoxylon species. We used a Linear Discriminant Analysis (LDA) to evaluate whether the three wasp species were well separated according to the morphological measurements. LDA was calculated with the psych package in R.

Usage Notes

Readme.txt

With these data, the reader is able to reproduce the analyses of niche breadth, niche overlap and discriminant analysis as it was indicated in the manuscript: Disentangling the coexistence strategies of mud-daubing wasp species through trophic analysis in oases of Baja California peninsula

The codes an steps to reproduce each analysis is given, indicating which library was used.

The dataset for niche overlap and niche breadth is contained in "Falcon-Brindis_general_table.csv" file. The scripts for this analysis are in the file "Niche_overlap_niche_breadth.R" The general table contains four columns: Spider = spider species name, T. scu = number of spiders captured by T. sculleni, T. dub = number of spiders captured by T. dubium, T. tri = number of spiders captured by T. tridentatum.

To compute the Linnear Discriminant Analysis (LDA), please open the file "LDA_wasp.R" and use the dataset "Falcon-Brindis_Wasp_body_measurements". The measurement data contains five columns: sex = the ID of each individual measure, thorax_L = thorax length, scutum = intertegular distance on scutum, head_w = head width, head_h = head high, wasp = wasp species.