DOI: 10.6078/d1fb14
title: Aquatic top predator prefers terrestrial prey in an intermittent stream

description: Ecosystems are often trophically entangled, sharing subsidies of energy
 and nutrients across habitat boundaries (e.g., forest to stream, stream to
 forest). In freshwater habitats surrounded by riparian vegetation, aquatic
 consumers may benefit from pulsed inputs of terrestrial organic matter,
 such as leaf litter and drowning organisms. This is especially pronounced
 in intermittent streams where the boundary between terrestrial and aquatic
 habitats is seasonally blurred. Over the past 10 years, we observed an
 aquatic insect predator Abedus indentatus (Hemiptera: Belostomatidae)
 largely feeding on terrestrial organisms in intermittent streams at
 Pinnacles National Park, California. To expand on these observations, we
 developed a behavioral assay where predators were presented with a range
 of prey comprising 11 species of various sizes from both aquatic and
 terrestrial habitats. We found that predator behavior was non-random and
 often influenced by prey characteristics. In particular, we found that
 predators tended to prefer large, terrestrial prey. Additionally, we found
 a positive relationship between size and strike probability among aquatic
 prey; however, this relationship did not hold for terrestrial prey items,
 indicating that certain size breakpoints might overcome increased levels
 of prey defense. Our results indicate that A. indentatus might favor prey
 items with weaker defenses within aquatic environments. However, other
 factors (i.e., prey size) might mediate foraging behavior. Because aquatic
 macroinvertebrate predators in intermittent streams depend on the
 terrestrial-aquatic interface, local predator dynamics may not be fully
 understood without considering fluxes of prey crossing ecosystem
 boundaries.
description: In order to detect patterns in prey
 preference with respect to size and origin (aquatic or terrestrial), we
 used a “prey-drop” assay similar to that of Hazarika and Goswami (2012)
 and Velasco and Millan (1998). This design allowed us to observe predator
 behaviors when simultaneously presented with a suite of prey representing
 a range of nutritional values and defensive capabilities. We gathered
 forty four specimens of <em>Abedus indentatus</em> from
 Chalone Creek in Pinnacles National Park, California, United States
 (36.46584, -121.15532) on May 28 and June 21, 2022. The land that now
 encompasses Pinnacles is contained within the ancestral territories of the
 Amah Mutsun and Chalone peoples, whose modern descendants maintain their
 eco-cultural heritage at the site. To capture our specimens, we conducted
 serial edge sampling and pool sweeps (3 each) using a 5 mm mesh net. Each
 sampling event covered roughly 100 m along the stream channel. Individuals
 were transported in 20 cm by 10 cm plastic containers with mesh tops for
 oxygenation and a handful of clean leaves and sticks from their home
 stream. They were housed under indirect natural light and fed commercially
 sourced mealworms (<em>Tenibrio molitor</em>) for 5-8 days.
 Food was withheld for 48 hours prior to testing to ensure that all
 specimens were hungry. Aquatic prey was collected on open space in San
 Geronimo, California, United States (Lat 38.01363, Long -122.65289) using
 serial edge sampling and pool sweeps, while terrestrial prey was captured
 via aerial netting, sweep-netting tall grass, and beating coast live
 oak.  Each treatment’s prey set
 consisted of one of each of the following: a smaller giant water bug
 Belostoma flumineum (wild caught, mean length 18.5 mm ± 2.06), a roach
 Blaptica dubia (commercially obtained, mean length 15.1 mm ± 1.7), a water
 boatman <em>Corixidae </em>sp. (wild caught, mean length 6.8
 mm ± 1.33), a cucumber beetle Diabrotica undecimpunctata (wild caught,
 mean length 5.6 mm ± 0.91), a diving beetle <em>Dytiscidae
 </em>sp. (wild caught, mean length 5.5 mm ± 0.5), an earwig
 Forficula auricularia (wild caught, mean length 12.2 mm ± 1.66), a larva
 and an adult of the damselfly <em>Ischnura </em>sp. (wild
 caught: adult mean length 27.5 mm ± 2.10; larva mean length 10.7 mm ±
 1.73), a backswimmer <em>Notonecta </em>sp. (wild caught, mean
 length 11.4 mm ± 1.2), and two size classes of the cricket Acheta
 domestica (commercially obtained, mean length 16.7 mm ± 1.41 for large
 specimens, mean length 8.2 mm ± 1.16 for small specimens). These prey
 items represent a range of sizes, as well as gradients of agility and
 physiological defense. Roughly half of the potential prey choices are
 primarily aquatic (<em>B. flumineum</em>, <em>Corixidae
 </em>sp., <em>Dytiscidae </em>sp., <em>nymphal
 Ischnura</em>, and <em>Notonecta</em>) while the
 remainder are terrestrial (<em>Blaptica dubia</em>,
 <em>D. undecimpunctata</em>, large and small Acheta, adult
 Ischnura, and Forficula). All prey types offered except for Blaptica were
 observed on riparian margins at Pinnacles during preliminary field
 observations, or were directly sampled in long-term benthic data (Apgar et
 al. unpublished data).    Each
 individual<em> A. indentatus</em> was tested in a 30 by 20 by
 20 cm acrylic observational arena fitted with a diagonal wooden perch.
 Water was sourced from San Geronimo Creek (38.01035, -122.65382). At the
 beginning of each assay, one <em>A. indentatus</em> was placed
 into the test arena alone and allowed to acclimate for 10-15 minutes.
 Following this acclimation period, a full set of prey items was dropped
 simultaneously and haphazardly into the observational arena with the
 <em>A. indentatus </em>(Figure 1 E). Each <em>A.
 indentatus </em>was observed over a 2-hour period which started at
 the time of the prey drop. Usually, three assays were conducted
 simultaneously, with the observer waiting until the first prey item from a
 treatment had been captured before moving on to the next to minimize
 inaccuracies related to human observational error. Captured prey items
 were taken from predators after 5 minutes using forceps to prevent them
 from feeding on only one prey item for the duration of the observational
 period. This allowed for higher resolution data on prey preference order.
 We quantified prey preference in two ways: 1) the binary response (attack
 or no attack) of each <em>A. indentatus</em> to each prey
 item, and 2) the order in which prey items were captured in each trial.
 For each assay, we also recorded the number of successful and failed
 predation attempts; the start, duration, and end of each predation event;
 and the time at which we removed a captured prey item. We used Plackett-Luce models to determine the worth
 of a given prey item when compared to other prey within a set. 
 Finally, to test if the size of a given prey
 item influenced the probability of selection, we calculated prey mean
 length by measuring 10 individuals of each prey species. We fitted
 logistic regressions for both aquatic and terrestrial prey items. All
 calculations were completed in R statistical software (R Core Team 2023)
 using an ɑ of 0.05.
description: We used R statistical software to analyze the data.
description: # Aquatic top predator prefers terrestrial prey in an intermittent stream
 \#This Readme pertains to the manuscript "Aquatic top predator
 prefers terrestrial prey in an intermittent stream" \#Authors: Amin
 M. al-Jamal, Albert Ruhi, Rose M. Mohammadi, Michael T. Bogan, Robert J.
 Fournier \#Dataset: “al-Jamal et al Belodata.csv” \#Dataset description:
 This dataset contains predator body length, experiment notes and the order
 in which prey were captured \#Columns: Specimen: Serial number of predator
 used in trial, life stage and notes on state of individual Body Length
 (mm): Length of the tested predator (in millimeters) Life Stage: Denotes
 whether the predator was an adult or a penultimate nymph Date of Trial:
 The date that the trial was conducted Prey Sequence (Terrestrial (T),
 Aquatic (A), Large (L), Small (S): The size category and origin of the
 prey- large aquatic prey was labelled as LA, small aquatic prey as SA,
 large terrestrial prey as LT, and small terrestrial prey as ST Ischnura
 Adult: A prey taxon- numbers in each row indicate the sequential order
 that that prey item was caught in a particular trial (eg. a prey item with
 ‘2’ in a row was the second prey item caught in that trial). NAs indicate
 that taxon was not targeted. Blaptica: A prey taxon- numbers in each row
 indicate the sequential order that that prey item was caught in a
 particular trial (eg. a prey item with ‘2’ in a row was the second prey
 item caught in that trial). NAs indicate that taxon was not targeted.
 Large Acheta: A prey taxon- numbers in each row indicate the sequential
 order that that prey item was caught in a particular trial (eg. a prey
 item with ‘2’ in a row was the second prey item caught in that trial). NAs
 indicate that taxon was not targeted. Diobrotica: A prey taxon- numbers in
 each row indicate the sequential order that that prey item was caught in a
 particular trial (eg. a prey item with ‘2’ in a row was the second prey
 item caught in that trial). NAs indicate that taxon was not targeted.
 Forficula: A prey taxon- numbers in each row indicate the sequential order
 that that prey item was caught in a particular trial (eg. a prey item with
 ‘2’ in a row was the second prey item caught in that trial). NAs indicate
 that taxon was not targeted. Small Acheta: A prey taxon- numbers in each
 row indicate the sequential order that that prey item was caught in a
 particular trial (eg. a prey item with ‘2’ in a row was the second prey
 item caught in that trial). NAs indicate that taxon was not targeted.
 Belostoma: A prey taxon- numbers in each row indicate the sequential order
 that that prey item was caught in a particular trial (eg. a prey item with
 ‘2’ in a row was the second prey item caught in that trial). NAs indicate
 that taxon was not targeted. Notonecta: A prey taxon- numbers in each row
 indicate the sequential order that that prey item was caught in a
 particular trial (eg. a prey item with ‘2’ in a row was the second prey
 item caught in that trial). NAs indicate that taxon was not targeted.
 Ischnura Nymph: A prey taxon- numbers in each row indicate the sequential
 order that that prey item was caught in a particular trial (eg. a prey
 item with ‘2’ in a row was the second prey item caught in that trial). NAs
 indicate that taxon was not targeted. Dytiscidae: a prey taxon- numbers in
 each row indicate the sequential order that that prey item was caught in a
 particular trial (eg. a prey item with ‘2’ in a row was the second prey
 item caught in that trial). NAs indicate that taxon was not targeted.
 Corixidae: A prey taxon- numbers in each row indicate the sequential order
 that that prey item was caught in a particular trial (eg. a prey item with
 ‘2’ in a row was the second prey item caught in that trial). NAs indicate
 that taxon was not targeted. Failed Strikes: The number of times in a
 trial that a predator struck at prey but failed to capture it Counts: The
 number of attacks made during that assay Notes Timestep 1: Time recorded
 (in minutes) for a prey capture or prey removal event/general notes. These
 are read from left to right for each trial with 1 event per cell. NAs
 indicate no notes. Notes Timestep 2: Time recorded (in minutes) for a prey
 capture or prey removal event/general notes. These are read from left to
 right for each trial with 1 event per cell. NAs indicate no notes. Notes
 Timestep 3: Time recorded (in minutes) for a prey capture or prey removal
 event/general notes. These are read from left to right for each trial with
 1 event per cell. NAs indicate no notes. Notes Timestep 4: Time recorded
 (in minutes) for a prey capture or prey removal event/general notes. These
 are read from left to right for each trial with 1 event per cell. NAs
 indicate no notes. Notes Timestep 5: Time recorded (in minutes) for a prey
 capture or prey removal event/general notes. These are read from left to
 right for each trial with 1 event per cell. NAs indicate no notes. Notes
 Timestep 6: Time recorded (in minutes) for a prey capture or prey removal
 event/general notes. These are read from left to right for each trial with
 1 event per cell. NAs indicate no notes. Notes Timestep 7: Time recorded
 (in minutes) for a prey capture or prey removal event/general notes. These
 are read from left to right for each trial with 1 event per cell. NAs
 indicate no notes. Notes Timestep 8: Time recorded (in minutes) for a prey
 capture or prey removal event/general notes. These are read from left to
 right for each trial with 1 event per cell. NAs indicate no notes. Notes
 Timestep 9: Time recorded (in minutes) for a prey capture or prey removal
 event/general notes. These are read from left to right for each trial with
 1 event per cell. NAs indicate no notes. Notes Timestep 10: Time recorded
 (in minutes) for a prey capture or prey removal event/general notes. These
 are read from left to right for each trial with 1 event per cell. NAs
 indicate no notes. Notes Timestep 11: Time recorded (in minutes) for a
 prey capture or prey removal event/general notes. These are read from left
 to right for each trial with 1 event per cell. NAs indicate no notes.
 Notes Timestep 12: Time recorded (in minutes) for a prey capture or prey
 removal event/general notes. These are read from left to right for each
 trial with 1 event per cell. NAs indicate no notes. Notes Timestep 13:
 Time recorded (in minutes) for a prey capture or prey removal
 event/general notes. These are read from left to right for each trial with
 1 event per cell. NAs indicate no notes. Notes Timestep 14: Time recorded
 (in minutes) for a prey capture or prey removal event/general notes. These
 are read from left to right for each trial with 1 event per cell. NAs
 indicate no notes. Notes Timestep 15: Time recorded (in minutes) for a
 prey capture or prey removal event/general notes. These are read from left
 to right for each trial with 1 event per cell. NAs indicate no notes.
 Notes Timestep 16: Time recorded (in minutes) for a prey capture or prey
 removal event/general notes. These are read from left to right for each
 trial with 1 event per cell. NAs indicate no notes. Notes Timestep 17:
 Time recorded (in minutes) for a prey capture or prey removal
 event/general notes. These are read from left to right for each trial with
 1 event per cell. NAs indicate no notes. Notes Timestep 18: Time recorded
 (in minutes) for a prey capture or prey removal event/general notes. These
 are read from left to right for each trial with 1 event per cell. NAs
 indicate no notes. Notes Timestep 19: Time recorded (in minutes) for a
 prey capture or prey removal event/general notes. These are read from left
 to right for each trial with 1 event per cell. NAs indicate no notes.
 Notes Timestep 20: Time recorded (in minutes) for a prey capture or prey
 removal event/general notes. These are read from left to right for each
 trial with 1 event per cell. NAs indicate no notes. Notes Timestep 21:
 Time recorded (in minutes) for a prey capture or prey removal
 event/general notes. These are read from left to right for each trial with
 1 event per cell. NAs indicate no notes. Notes Timestep 22: Time recorded
 (in minutes) for a prey capture or prey removal event/general notes. These
 are read from left to right for each trial with 1 event per cell. NAs
 indicate no notes. \#Dataset: “al-Jamal et al Strikes.csv” \#Dataset
 description: This dataset contains size and origin (aquatic vs
 terrestrial) information on each individual prey item from each trial, as
 well as wether or not they were successfully preyed upon \#Columns: Assay
 #: Trial number of the individual prey item being addressed in the row
 Species: The taxon of the individual prey item being addressed in the row
 Size: The mean size of the prey taxon from the species column Group: The
 bin (origin and size) of the prey taxon from the species column Attacks:
 Binary response to indicate if a prey item was attacked (1 for yes, 0 for
 no) Fails: Binary response to indicate if a prey item was the victim of a
 failed strike (1 for yes, 0 for no) \#Dataset: “al-Jamal isotopes.csv”
 \#Dataset description: This dataset contains isotopic data for wild caught
 innvertebrates from Pinnacles National Park \#Columns: ID: Specimen ID
 Individual: Individual number Replicate: Replicate ID Taxa: Organismal
 type Group: Trophic level per_N: Percentage of N isotopes in sample ug_N:
 Micrograms of N in the sample d15N: Micrograms of N15 in sample per_C:
 Percent Carbon of sample mg_C: Milligrams of carbon in sample d13C: Amount
 of C13 in sample \#Dataset: “al-Jamal et al p a ratios.csv” \#Dataset
 description: This dataset contains area, perimeter, and P/A ratios data of
 6 intermittent stream pools in our study area (Chalone Creek watershed,
 Pinnacles National Park, California), oceanic islands (n=19; Polis et al.,
 1998), vernal pools (n=34; Brooks & Hayashi, 2002), and a global data
 set on lakes (n=1,420,891; Messager et al., 2016). \#Columns: Name: Name
 of the lake, vernal pool, oceanic island, or intermittent stream pool
 Ecosystem: Category of ecosystem area_km2: Area (in km2) perimeter_km:
 Perimeter (in km) p_a_ratio_km: Perimeter to area ratio (in km/km2)
 Source: Dataset citation \#Data were analyzed using R statistical
 software. See attached code "al-Jamal et al code.R" for usage