Data from: Grasshoppers do not flee from their alarmed predators but from non-alarmed ones
Data files
Aug 05, 2024 version files 22.26 KB
-
Raw_data.xlsx
20.24 KB
-
README.md
2.02 KB
Abstract
Alarm calls produced by basal prey have well-known informative value. In multipredator communities, mesopredators, when faced with top predators, may emit alarm calls that could inform basal prey about their lowered predation risk. To test this unexplored possibility, we conducted one field and one mesocosm experiment in which we simulated alarm and non-alarm calls from little owls (Athene noctua) as mesopredators and measured their effects on grasshoppers as prey of little owls but not of top predators. In the field experiment, we found that grasshopper species were significantly more abundant in patches where we simulated either the presence of scared little owls (alarm treatment) or no owls (control treatment) compared to patches where the presence of non-scared little owls (non-alarm treatment) was simulated. In the mesocosm experiment, locusts’ (Locusta migratoria) moved significantly more to exposed areas when we simulated the presence of scared little owls (alarm treatment) or of a granivorous bird (control treatment), while they moved to sheltered areas when we simulated the presence of non-scared owls (non-alarm treatment). These results show that prey could cue on predators’ calls to assess their predation risk and make decisions, revealing unprecedented potential ecological consequences of alarm calls in invertebrate communities.
README: Grasshoppers do not flee from their alarmed predators but from non-alarmed ones
https://doi.org/10.5061/dryad.tht76hf7c
We provide data obtained in a large-scale field experiment (first sheet) and in a mesocosm experiment (second sheet) to study the response of grasshoppers to different calls of their predators.
Description of the data and file structure
In the first sheet, we provide the data extracted from the Field experiment. Variables used were:
Transect_ID = Identification of the transect
Patch= Experimental patch
Treatment =Call treatment as Alarm, Non-alarm or Control
Julian_date = date expressed as the number of days since the first of January
Juliandate_class = classification of the transects as early or late according to whether they were carried out before or after the median date value
Grasshoppers_abundance = Number of counted grasshoppers per transect
Size(m2) = Patch size in m2. Only one value per patch is provided, so that patch size can be compared among treatments avoiding pseudoreplication.
Missing data code: n/a
In the second sheet, we provide the data extracted from the Mesocosm experiment. Variables used were:
Mesocosm_ID = Identification of the mesocosm
Julian_date1 = Date of the first day of each experiment expressed as the number of days since the first of January
Tmax_1 = Maximum temperature in degrees Celsius during the recording of locust behavior during the first day of each experiment
Tmax_2 = Maximum temperature in degrees Celsius during the recording of locust behavior during the second day of each experiment
dif_tmax =Difference of maximum temperature in degrees Celsius between the two experimental days in each experiment
%locusts_moved_to_exposed_hab = Difference of percentage of locusts in the exposed habitat from the first to the second day of the experiment
Treatment =Call treatment as Alarm, Non-alarm or Control
Methods
Firstly, in a field experiment we sampled the abundance of several grasshopper species in patches after broadcasting repeatedly for several days either little owls’ alarm calls (alarm treatment, simulating scared owls) or non-alarm/contact calls (non-alarm treatment, simulating non-scared owls), or just visiting the patches (control treatment, simulating no owls). In addition, in a mesocosm experiment, we recorded the distribution of migratory locusts (Locusta migratoria) in exposed and sheltered areas before and after broadcasting little owls´ alarm calls (alarm treatment), non-alarm/contact calls (non-alarm treatment) or vocalizations of a woodpigeon (Columba palumbus) as a granivorous, non-predator bird for grasshoppers (control treatment).
The abundance of grasshoppers in the field experiment were sampled in all patches by counting all detected individuals, either inactive or during their flights/jumps, while walking at constant speed (about 2 km per hour) along longitudinal transects 50 m long and with a 5-m band. The number of grasshoppers was used as the response variable to the call treatment because it is a proxy of insect abundance as prey of little owls.
In the mesocosm experiment, locusts behavior was recorded with video cameras and we counted the proportion of individuals in exposed areas at the end of pre-treatment and treatment conditions (day 1st and 2nd of the trials) and calculated the difference as a measure of preference to be exposed versus hidden in response to the call treatments.