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A long-term evaluation of the interacting effects of fire and white-nose syndrome on endangered bats: final report to JFSP

Author(s): Luke E. Dodd, Matthew B. Dickinson, Michael J. Lacki, Lynne K. Rieske, Nick Skowronski, Steven C. Thomas, Rickard S. Toomey III
Year Published: 2019

Habitat use of bats may shift following population-level impacts of white-nose syndrome (WNS). Specifically, the effect of WNS across forest landscapes is unclear in relation to prescribed fire. Mammoth Cave National Park (MACA) has employed a prescribed fire regime since 2002, and WNS was detected on MACA in 2013. Thus, project #14-1-05-22 carried on past efforts of project #10-1-06-1, wherein bat activity was monitored across burned and unburned sites at MACA before (2010-2012) and after the detection of WNS (2013-2016) using acoustic detectors concurrent with insect survey techniques. Acoustic recordings of bats were classified to phonic groups (low, mid, Myotis sp. - MYO). There was a significant interaction between WNS and prescribed fire for the MYO phonic group, and activity levels of all phonic groups shifted after WNS appeared at MACA. Insects in blacklight traps were greater after WNS, with a trend towards unburned areas for Lepidoptera and burned areas for Coleoptera. Our data indicate substantial changes in both bat and insect composition at MACA concurrent with the arrival and impact of WNS.

From there we expanded our efforts to understand fire, predator, and prey in a post-WNS context. Lepidoptera are a core resource for many bats. These predators consume Lepidoptera of varying sizes. Considering this, we explored the relationships between caloric yield, body size, and wing presence using lab-reared and field-collected insects. Bomb calorimetry studies indicated that lab- and field-collected insects of varied species and sizes were of similar energetic quality on a per mass basis, thus we then assessed habitat quality for bats at MACA on the basis of insect capture rates and broader nutrient parameters reported for insects in the literature. We modeled the effects of WNS, fire, and insect availability on bat assemblage diversity and composition. To facilitate this, Lepidoptera were clustered into six classes defined by wingspan and characterized by dry mass and caloric value. Mean wingspan of prey differed across all size classes, suggesting our prey classification was effective. The best-fitting model for diversity of bat phonic groups included the relative abundance of dominant insect orders as well as WNS. A dbRDA was used to further define relationships between bats, insects and fire. The indirect effects of WNS on Lepidoptera are still not fully resolved, but our research suggests shifts in the composition of this assemblage following the arrival of WNS at MACA (in addition to our observations of shifting abundance). Expanding on our modeling efforts, we sought to establish a nutritional geometry framework for understanding habitat selection by bats at MACA. We estimated mean C:N ratios and elemental compositions of Coleoptera, Diptera, Hymenoptera, and Lepidoptera, and developed cumulative nutritional profiles for burn management units at MACA. We found that insect abundance and C:N ratios were not spatially autocorrelated. The distribution of nutrients in insects is not uniform across MACA, and does not align with simple prey abundance.

Finally, we sought to evaluate the impacts of varying fire exposure, burn history, on the regeneration and herbivory of hardwood species. Because of its historic loss from eastern deciduous forests, little is known about the effects of fire on Castanea dentata (CADE, American chestnut). In our study, forest soil was collected from a recent wildfire and from an adjacent unburned area to grow blight-resistant backcrossed CADE seeds in a 2×2 design in the greenhouse. Seedlings grown in burned soil and full sun had greater height growth and leaf availability than those grown in unburned soil and shade. Feeding assays with Lymantria dispar dispar (LYDI, European gypsy moth) indicate that caterpillars may not alter their consumption of chestnut seedlings grown in soil burned by fire, but they may not grow as large under the increased light typical of burned forests. Understanding the effects of fire on hardwood species, and discerning how fire may influence its native and non-native insect associates, is essential for the long-term success of hardwood regeneration.

We show that although WNS is obviously the primary factor impacting the abundance and distribution of bats at MACA, prescribed fire and insect communities contribute to observed patterns in bat assemblage diversity and composition. Further, we document post-WNS shifts in insect communities. Although the extent to which prey and land management may shape persistent bat assemblages remains unclear given the overwhelming influence of WNS, we have provided evidence that a relationship between bat foraging ecology, insects, and fire persists despite devastating declines. The implications of this work are optimistic: fundamental habitat associations and predator-prey dynamics appear largely unchanged, indicating that conservation efforts emphasizing prey availability and habitat manipulation may provide some degree of support to imperiled bats.

Citation: Luke E. Dodd, Matthew B. Dickinson, Michael J. Lacki, Lynne K. Rieske, Nicholas K. Skowronski, Steven C. Thomas, and Rickard S. Toomey III. 2019. A Long-Term Evaluation of the Interacting Effects of Fire and White-Nose Syndrome on Endangered Bats - Final Report to Joint Fire Science Program. JFSP PROJECT ID: 14-1-05-22. Eastern Kentucky University, Department of Biological Sciences, 38p.
Topic(s): Fire Effects, Ecological - Second Order, Wildlife, Fire & Wildlife, Mammals
Ecosystem(s): None
Document Type: Technical Report or White Paper
NRFSN number: 19455
Record updated: Jun 4, 2019