Seasonal bat activity related to insect emergence at three temperate lakes.

Ioanna Salvarina,Karl-Otto Rothhaupt,Dorian Gravier

doi:10.1002/ece3.3943

Abstract

Knowledge of aquatic food resources entering terrestrial systems is important for food web studies and conservation planning. Bats, among other terrestrial consumers, often profit from aquatic insect emergence and their activity might be closely related to such events. However, there is a lack of studies which monitor bat activity simultaneously with aquatic insect emergence, especially from lakes. Thus, our aim was to understand the relationship between insect emergence and bat activity, and investigate whether there is a general spatial or seasonal pattern at lakeshores. We assessed whole‐night bat activity using acoustic monitoring and caught emerging and aerial flying insects at three different lakes through three seasons. We predicted that insect availability and seasonality explain the variation in bat activity, independent of the lake size and characteristics. Spatial (between lakes) differences of bat activity were stronger than temporal (seasonal) differences. Bat activity did not always correlate to insect emergence, probably because other factors, such as habitat characteristics, or bats’ energy requirements, play an important role as well. Aerial flying insects explained bat activity better than the emerged aquatic insects in the lake with lowest insect emergence. Bats were active throughout the night with some activity peaks, and the pattern of their activity also differed among lakes and seasons. Lakes are important habitats for bats, as they support diverse bat communities and activity throughout the night and the year when bats are active. Our study highlights that there are spatial and temporal differences in bat activity and its hourly nocturnal pattern, that should be considered when investigating aquatic–terrestrial interactions or designing conservation and monitoring plans.

Highlights

Spatial or allochthonous subsidies are resources that originate in a donor habitat and enter into a food web of a recipient habitat and possibly alter its consumer-resource dynamics (Polis, Anderson, & Holt, 1997)
The amount of aquatic insects entering the terrestrial systems that is available to terrestrial consumers and whether this food resource fluctuates seasonally is less studied (e.g., Salvarina et al, 2017), with responses to bat activity
When the models were applied for each lake separately for the whole dataset, the models that explained the bat activity variation the best were those with insects, wind speed, and temperature in Lake Constance and Siechenweiher and the one with insects, season, and wind in Mindelsee (Table 3)

Summary

| INTRODUCTION

Spatial or allochthonous subsidies are resources that originate in a donor habitat and enter into a food web of a recipient habitat and possibly alter its consumer-resource dynamics (Polis, Anderson, & Holt, 1997). The amount of aquatic insects entering the terrestrial systems that is available to terrestrial consumers and whether this food resource fluctuates seasonally is less studied (e.g., Salvarina et al, 2017), with responses to bat activity. Studying aquatic–terrestrial interactions is an important topic in ecology with increasing interest (e.g., Gratton, Donaldson, & Vander Zanden, 2008; Bartrons, Papes, Diebel, Gratton, & Vander Zanden, 2013) and implications, such as in helping to: (1) investigate and possibly predict the effects of climate change and eutrophication of waters on terrestrial consumers, (2) study food webs, (3) manage the conservation of ecosystems and species effectively, and (4) track transfer of contaminants from aquatic to terrestrial systems (Mogren, Walton, Parker, & Trumble, 2013). Activity patterns of bats are suggested as a monitoring tool of animal responses to long-term changes in climate, as it is related to climate and weather conditions (Frick et al, 2012)

| MATERIALS AND METHODS

| DISCUSSION

Findings

| General conclusions and recommendations