Niche Partitioning in Neotropical Scorpions

Top: Three species collected at the Los Tuxtlas Field Station: Centruroides rileyi (left), Centruroides flavopictus (middle), Centruroides gracilis (right)
Bottom: Three habitat types at the Los Tuxtlas Field Station: Primary (left), Secondary (middle), and Pastureland (right). 


Scorpions are an ancient group of predatory arachnids originating in the Middle Silurian (438 mya). Over 2400 species and 19 families are currently recognized, inhabiting all continents except Antarctica. Scorpion habitats range from deserts and savannas to temperate and tropical forests to the intertidal zone, and snow-covered mountains. Some scorpion lineages are highly endemic and have specialist habitat requirements, while others are generalists and opportunistic, making them good colonizers. Scorpions are k-selected or equilibrium species, inhabiting stable and predictable microhabitats, having low degrees of interspecific interaction with little population fluctuation, and can occupy specialized niches. Finally, scorpion microhabitat preference is roughly divided into two broad categories: ground-dwelling species which live in burrows, leaf litter, rocks, bark, and arboreal species found at various heights in vegetation. Overall, scorpions provide a suitable study system to examine niche partitioning. 

Species in the scorpion genus Centruroides (Scorpiones: Buthidae) are good candidates for the study of ecological niche partitioning because of their habitat plasticity, widespread geographic distribution, and presence of cryptic species. Currently, three species belonging to three subgroups of Centruroides are distributed along the Isthmus of Tehuantepec in southern Mexico, presenting a rare opportunity to study niche partitioning within a single genus. We examined the environmental, substrate, and habitat conditions of Centruroides flavopictus, Centruroides gracilis, and Centruroides rileyi within Estación de Biología Los Tuxtlas, west of the Isthmus of Tehuantepec. Our results demonstrate habitat partitioning occurs along humidity, temperature, and elevational gradients: individuals of C. gracilis were found in habitats of low humidity and high temperature, and were predominantly found on the substrate in human‐mediated habitats; individuals of C. flavopictus were found in a larger range of humidity and temperature conditions within secondary and primary forest; and individuals of C. rileyi had the greatest habitat specificity, and were found in conditions of low temperature and high humidity on trees within primary forest. Furthermore, individuals of C. rileyi were found significantly higher in trees than those of C. flavopictus. This study represents the first example of niche partitioning within a genus of scorpion, and the first description of the ecological niche in an arboreal‐specialist scorpion.

Here is the paper (left) ! I also made the cover of Invertebrate Biology with a photograph of C. gracilis ​(Right). 

Systematics of Arboreal Scorpions

Top: In-situ photographs of members of the 'thorelli' clade demonstrating their arboreal ecology and unique morphology.
Bottom: Ultraviolet photographs of external morphology of members of the 'thorelli' clade: Pectines & Sternites (left), Carapace (middle), and Chela (right).
The ‘thorelli’ clade is the smallest clade (four species) within Centruroides, and is strongly monophyletic. Among the groups proposed by previous researchers, the ‘thorelli’ clade is particularly unique due to its unusual morphology (elongated metasoma and sting) and canopy-dwelling habitat. Historically, the placement of species within the ‘thorelli’ clade has been based on distribution in southern Mexico and northern Central America and unique morphology. However, this small clade has been plagued with inaccurate taxonomy resulting from morphological convergence. There also appears to be many cryptic species among the ‘thorelli’ clade, roughly 50% of the species diversity is currently recognized and potentially needing to be split. Such inaccuracies are due to undersampling and damaged museum material (personal observation). Throughout my masters degree I traveled to several museums, and collected new material from both Mexico and Guatemala. Current research involves a phylogenetic and taxonomic revision of the subgenus, including species delimitation analyses and the description of four new species. I plan on naming a new species after my grandfather, as gratitude for first introducing me to biology. 

Niche Partitioning in California Scorpions

Top: Three species found within Mount Diablo State Park: Uroctonus mordax, (left), Paruroctonus silvestrii, (middle), and Serradigitus gertschi, (right).
Bottom: Three habitat types within Mount Diablo State Park: Grassland (left), Oak Woodland (middle), Chaparral (right).
The California Floristic Province (CFP) is one of only five regions in the world with a Mediterranean-type climate and is considered a ‘biodiversity hotspot’. The CFP possesses over 5000 species of plants and vertebrate animals, 40% of which are endemic. Over 50 species of scorpion are found in California (iNaturalist.org). Surprisingly, the majority of ecological and diversity research conducted on scorpions within California has been restricted to Baja, while other diverse localities have been largely neglected. Due to its varied landscape and forest types, microhabitats, geologic heterogeneity, and high degrees of endemism, Mt. Diablo State Park, 30 miles north-east of San Francisco presents an ideal opportunity to understand niche use among California scorpions.

Mt. Diablo is the single most important wildlife habitat in the east bay due to its varied topography, and environmental influences from the coast, Central Valley, and San Francisco Bay Delta. Mt. Diablo possesses at least 253 vertebrate species, and over 900 plant species; three quarters of which are native. Furthermore, Mt. Diablo harbors more than 150 species which are rare or listed as endangered, eleven of which are endemic to the region. Currently three species of scorpion inhabit the park in sympatry, each of which differ in size, habitat use, and evolutionary history.

The aim of this study was to examine the environmental, substrate, and habitat preferences of Uroctonus mordax, (Vaejovidae) Thorell 1872, Paruroctonus silvestrii, (Vaejovidae) Borelli 1909, and Serradigitus gertschi, (Vaejovidae) Williams 1968, inhabiting Mt. Diablo State Park. No previous studies have examined niche use among scorpions within the San Francisco Bay Area. Using the same ecological field techniques as my research in mexico, we determined that the three species studied exhibit niche partitioning by altitude, humidity, temperature, height, substrate, and vegetation type. 

Here is a blog post about our findings!