Geometric morphometric analysis of red fox (Vulpes vulpes) skulls using radiometric techniques at three and six months of development

BACKGROUND

Morphological growth naturally progresses with age; however, the rate of growth varies across different parts of an organism, with certain structures developing more rapidly than others. This study aimed to analyze and compare the skull development of red foxes (Vulpes vulpes) during two specific developmental stages: the 3rd and 6th months, which represent distinct growth phases in their early ontogeny.

METHODS

In this study, we aimed to analyze and compare skull development in red foxes (Vulpes vulpes) during two specific post-natal time points: the 3rd and 6th months. Shape analysis was performed using radiographic images of nine red foxes at both the third and sixth months.

RESULTS

Shape differences were observed in the skulls of red foxes (Vulpes vulpes) at these two ages. Our findings confirmed the hypothesis that skull shape changes over time, reflecting distinct morphological adaptations associated with age-related growth. In the measurements at the 3rd month, the neurocranial region exhibited a more distinct and developed structure compared to the facial bones. Toward the 6th month, the skull displayed a thinner and more elongated structure with the further development of the facial bones.

CONCLUSIONS

This difference indicates a period of rapid growth and development in the neurocranial area, suggesting that red foxes experience significant neurological and sensory development early in life. Future studies on skull shape variation across different developmental stages in red foxes can expand on these findings. Age-related morphological studies, such as this one, provide essential baseline data on the natural growth and development of wild species like red foxes. This knowledge is essential for identifying deviations from normal development, which could result from environmental stressors, habitat changes, or malnutrition.

Assessing springtime vertebrate prey of sympatric mesopredators in the southeastern United States using metabarcoding analysis

Coyotes (Canis latrans) colonized the eastern United States over the last century and formed a 3-species predator guild with bobcats (Lynx rufus) and gray foxes (Urocyon cinereoargenteus) across much of the southeastern United States. Diets among the three species vary along with respective impacts on game species such as white-tailed deer (Odocoileus virginianus) and wild turkeys (Meleagris gallopavo). To determine predation impacts on vertebrate prey and dietary overlap in consumption of prey items, we assessed diets of coyote, bobcat, and gray fox during spring, coinciding with white-tailed deer fawning and wild turkey nesting and brood rearing. We sampled across three sites along the Savannah River in South Carolina from mid-May through mid-June of 2020-2021. We collected 180 scat samples along 295.9 kilometers (71.1-122.4 km/site) of unpaved secondary roads and used DNA metabarcoding to determine vertebrate diet items. We identified predator species of scat using DNA metabarcoding and species-specific mtDNA fragment analysis (153 were coyote, 20 bobcat, and seven gray fox). Overall, we found evidence that two species, coyote and bobcat, consumed deer while all three consumed turkeys. Frequency of deer in the diet varied across sites for coyotes from 62-86% and wild turkey was present with a frequency of occurrence of 9% for coyotes, 5% for bobcats, and 14% for gray fox. Vertebrate diet specialization was evident across predator species with high frequency of deer in coyote diets, rabbits and small mammals in bobcat diets, and herpetofauna in gray fox diets. During deer fawning and wild turkey nesting and brood rearing, dietary overlap appears to be mediated by disparate selection of prey items, which reduced competition among coyotes, bobcats, and gray foxes. Use of DNA metabarcoding may augment our understanding of dietary preferences within this predator guild by providing increased resolution of diet composition among important game species.

Asymmetrical intraguild interactions with coyotes, red foxes, and domestic dogs may contribute to competitive exclusion of declining gray foxes

Species coexistence is governed by availability of resources and intraguild interactions including strategies to reduce ecological overlap. Gray foxes are dietary generalist mesopredators expected to benefit from anthropogenic disturbance, but populations have declined across the midwestern USA, including severe local extirpation rates coinciding with high coyote and domestic dog occurrence and low red fox occurrence. We used data from a large-scale camera trap survey in southern Illinois, USA to quantify intraguild spatial and temporal interactions among the canid guild including domestic dogs. We used a two-species co-occurrence model to make pairwise assessments of conditional occupancy and detection rates. We also estimated temporal activity overlap among species and fit a fixed-effects hierarchical community occupancy model with the four canid species. We partitioned the posterior distributions to compare gray fox occupancy probabilities conditional on estimated state of combinations of other species to assess support for hypothesized interactions. We found no evidence of broadscale avoidance among native canids and conclude that spatial and temporal segregation were limited by ubiquitous human disturbance. Mean guild richness was two canid species at a site and gray fox occupancy was greater when any combination of sympatric canids was also present, setting the stage for competitive exclusion over time. Domestic dogs may amplify competitive interactions by increasing canid guild size to the detriment of gray foxes. Our results suggest that while human activities can benefit some mesopredators, other species such as gray foxes may serve as bellwethers for habitat degradation with trophic downgrading and continued anthropogenic homogenization.