How moths escape bats: predicting outcomes of predator-prey interactions

2018

Preprint

11 1. Many prey species overlap in time and space and are hunted by the same predators. A common 12 anti-predator behaviour are evasive manoeuvres to escape an attacking predator. The escape-tactic 13 diversity hypothesis postulates that species-specific differences in evasive behaviour will increase 14 the overall unpredictability experienced by predators within a predator-prey community. 15Evolutionary, escape-tactic diversity would be driven by the enhanced predator protection for each 16 prey individual in the community. However, escape-tactic diversity could also be a functional 17 consequence of morphological differences that correlate with evasive capabilities. 18 2. Echolocating bats and eared moths are a textbook example of predator-prey interactions. Moths 19 exhibit evasive flight with diverse tactics; however, the variability of their evasive flight within 20and between species has never been quantified systematically. In addition, moth species show 21 variation in size, which correlates with their flight capability. 223. We recorded flight strength during tethered flight of eight sympatric moth species in response to 23 the same level of simulated bat predation. Our method allowed us to record kinematic parameters 24 that are correlated with evasive flight in a controlled way to investigate species-specific 25 differences in escape tactics. 26 4. We show species-specific and size-independent differences in both overall flight strength and 27 change of flight strength over time, confirming the escape-tactic diversity hypothesis for eared 28 moths. Additionally, we show strong inter-individual differences in evasive flight within some 29 species. This diversity in escape tactic between eared moths increases the overall unpredictability 30 of evasive flight experienced by bat predators, likely providing increased protection against 31 predatory bats for the single individual. 32 33 KEYWORDS 34 anti-predator behaviour, comparative analysis, escape-tactic diversity, last-ditch evasive flight, 35 Lepidoptera, mixed-species benefits 36 Georgiev for help with data collection, Fränzi Korner-Nievergelt and Tobias Roth for statistical 388 advice, and Sue Anne Zollinger for comments on a previous version this manuscript. 389 390 FUNDING 391 Deutsche Forschungsgemeinschaft (Emmy Noether research grant GO2029/2-1 to H.R.G.) 392 IMPRS for Organismal Biology (to T.H.) 393

Section: Results 213supporting

confidence: 56%

Section: Introduction 37mentioning

confidence: 99%

Species-specific strategies increase unpredictability of escape flight in eared moths

Huegel

2018

Preprint

“…Since the A2 cell threshold was exceeded at 1.4 m bat–moth distance, only moths with comparably long reaction times (>203 ms) would not initiate any last‐ditch manoeuvre. If moths were able to initiate a last‐ditch manoeuvre, power dives or other downward‐directed flight manoeuvres might prove most effective, since barbastelles mostly attacked from below and escape trajectories towards the bat are most successful (Corcoran & Conner, ). Even if the moth just initiated a last‐ditch manoeuvre, however, bats might still be able to catch it with their wing (wingspan about 25–28 cm; Rydell & Bogdanowicz, ).…”

Section: Discussionmentioning

confidence: 99%

Continued source level reduction during attack in the low‐amplitude bat Barbastella barbastellus prevents moth evasive flight

Lewanzik

2018

Functional Ecology

Ears evolved independently in many insect taxa due to the selection pressure of echolocating bats. Eared moths perform evasive flight manoeuvres upon hearing approaching bats, thereby substantially increasing survival probability. Accordingly, eared moths constitute only a minor portion of many bats’ diets. In contrast, the barbastelle bat Barbastella barbastellus almost exclusively feeds on eared moths by emitting low‐amplitude stealth echolocation calls that are undetectable by distant moths. While closing in on the prey, however, the calls might become audible. We thus hypothesised that barbastelle bats lower the source level of their calls even further while closing in, such that the level at the moth's ear remains below the moth's hearing threshold and the moth fails to elicit its evasive manoeuvre. We tested these hypotheses by offering tethered moths to barbastelle bats in the wild and in captivity. We reconstructed the bats’ three‐dimensional flight paths based on time‐of‐arrival differences of the echolocation calls at four microphones, measured the received sound levels at the moth's position with an additional miniature microphone, and calculated call source levels. We show that barbastelle bats continuously reduced source level upon detecting a moth, thereby delaying the time and shortening the distance when the moth might detect the bat. The received level at the targeted moth never exceeded the moth's neuronal hearing threshold by more than 10 dB, which is likely sufficiently low to prevent moth evasive flight. Barbastelle bats emit low‐amplitude calls to counter moth hearing. Continued amplitude reduction during an attack extends the time before the prey becomes aware of the predator, if at all. In combination, these two strategies allowed barbastelle bats to access a food resource which is largely unavailable to competing species, thereby probably altering competition between sympatric predators. A http://onlinelibrary.wiley.com/doi/10.1111/1365-2435.13073/suppinfo is available for this article.

“…lacking airflow and self‐motion) and their flight behaviour (Taylor, ). Although free‐flight experiments will be required to link vertical flight strength in tethered flight to actual three‐dimensional flight trajectories, free‐flight studies showed a clear change of kinematic parameters during last‐ditch evasive flight (Corcoran & Conner, , ). Our observations are further supported because the reaction of a given species was independent of whether individuals were flying or not at stimulus onset.…”

Section: Discussionmentioning

confidence: 99%

“…We analysed wing surface area as one size‐related explanatory variable underlying potential species‐specific differences in evasive flight. We used vertical flight strength as proxy for flight speed, which, like many other variables, increases when moths actively perform last‐ditch evasive flight (Corcoran & Conner, , ). Even though tethered flight does not allow us to study actual 3D flight behaviour, measurements of flight strength and its temporal variation revealed species‐specific strategies, and corresponding interspecific differences, in evasive flight.…”

Section: Introductionmentioning

confidence: 99%

Species‐specific strategies increase unpredictability of escape flight in eared moths

Hügel

2019

Functional Ecology

Many prey species overlap in time and space and are hunted by the same predators. A common anti‐predator behaviour is using evasive manoeuvres to escape an attacking predator. The escape‐tactic diversity hypothesis postulates that species‐specific differences in evasive behaviour will increase the overall unpredictability experienced by predators within a predator–prey community. Evolutionary, escape‐tactic diversity would be driven by the enhanced predator protection for each prey individual in the community. However, escape‐tactic diversity could also be a functional consequence of morphological differences that correlate with evasive capabilities. Echolocating bats and eared moths are a textbook example of predator–prey interactions. Moths exhibit evasive flight with diverse tactics; however, the variability of their evasive flight within and between species and individuals has never been quantified systematically. In addition, moth species show variation in size, which correlates with their flight capability. We recorded flight strength during tethered flight of eight sympatric moth species in response to the same level of simulated bat predation. Our method allowed us to record kinematic parameters that are correlated with evasive flight in a controlled way to investigate species‐specific differences in escape tactics. We show species‐specific and size‐independent differences in both overall flight strength and change of flight strength over time, supporting the escape‐tactic diversity hypothesis for eared moths. Additionally, we show strong interindividual differences in evasive flight within some species. This diversity in escape tactic between eared moths increases the overall unpredictability of evasive flight experienced by bat predators, likely providing increased protection against predatory bats for the single individual.