DOI: 10.5061/dryad.gf1vhhn0v
title: Data from: Warming speeds up range expansion in an experimental model system

description: Dispersal is becoming increasingly critical to understand as climate
 change is forcing species to shift their ranges to track changing
 environments. While we know that warmer temperatures can prompt range
 shifts, there is little known about how temperature influences the
 capacity for organisms to move by changing rates of range expansion.
 Warmer temperatures could affect the range expansion rate through two
 pathways: by increasing random, density-independent movement via increased
 metabolic rates, and/or by increasing population growth rates and driving
 density-dependent movement. Surprisingly, there have been no experimental
 tests of the effect of temperature on range expansion rate. We used red
 flour beetles, Tribolium castaneum, to test the overall effect of
 temperature on the rate of range expansion and to determine if random
 movement, population density, or both could be driving this
 effect. We grew beetle populations in linear connected landscapes at three
 temperatures (27.5 °C, 30 °C, and 32.5 °C) and tracked their expansion
 across these landscapes for 18 weeks. We then conducted separate assays to
 isolate the effects temperature on movement (density-independent dispersal
 probability) and on population growth rates. We found a positive effect of
 temperature on range expansion rate, with beetles in the 32.5 °C
 exhibiting the fastest range expansion. We also found positive effects of
 temperature on both dispersal probability and on population growth rate,
 indicating that both processes are likely contributing to this overall
 effect. Our findings highlight the importance of integrating the effects
 of temperature on range expansion speed in order to fully understand how
 quickly, species’ ranges could shift under climate change. 
description: <strong>Main experiment</strong>
 We tested the effect of temperature on the rate of range
 expansion in <em>Tribolium castaneum</em> flour beetles across
 experimental linear landscapes in three temperature treatments. Landscapes
 were made up of 12 acrylic boxes (4 cm x 4 cm x 6 cm), where each box
 represented an individual habitat patch. We filled each patch with 30 g of
 a mix of a high-quality and a low-quality resource for this species (60 %
 whole wheat flour and 40 % rice flour). We used this mixed flour medium in
 order to temper population growth and make tracking population sizes
 logistically feasible. Patches were arranged in a single row and held
 together with elastic bands. Each patch had a 2-mm diameter hole drilled
 beneath the flour level on each side to allow for dispersal between
 patches. We established ten replicate landscapes at
 each of three temperatures: 27.5 °C, 30 °C, and 32.5 °C. The historic
 temperature of our laboratory strain was 30C and the thermal optimum for
 this species is 30-31 °C. Landscapes were maintained in temperature- and
 humidity- controlled incubators (treatment temperature ± 0.5 °C, 50 %-70 %
 relative humidity). To control for any variation across incubators, we
 swapped treatments across chambers each month. Each
 landscape was established by introducing 20 adult <em>T.
 castaneum</em> beetles into the first patch. Landscapes were then
 placed in their respective incubators for a three-week period to allow
 beetles to create tunnels in which to move through the flour. During this
 no-dispersal phase of the study, dispersal holes were blocked with acetate
 strips. After three weeks, the acetate strips were removed for 12 hours to
 allow for controlled dispersal into neighboring patches. After 12 hours,
 the acetate strips were added back in place to block the holes, and the
 landscapes were disassembled for population censusing. To census
 populations, we first inspected each patch in each landscape for signs of
 beetle activity (i.e., tunnels in the flour). We then sifted the flour out
 of all patches with any sign of beetle activity as well as the next two
 seemingly empty patches (to ensure no beetle presence). For any patch that
 contained adult beetles or larvae, we counted all live and dead adult
 beetles and replaced half of the flour medium with fresh flour medium.
 Upon completion of the count, beetles were placed back into their
 respective patches and landscapes were reassembled in the same order,
 placed back in their respective incubators, and the three-week cycle
 started again. This was repeated six times, for a total experimental
 duration of 18 weeks. <strong>Movement rate
 assay</strong> To determine the direct effect of
 temperature on movement rates (independent of the effect of temperature on
 population growth rates), we conducted a separate experiment. The
 experimental set-up was similar to that of the main experiment (same three
 temperatures and same flour medium), however landscapes consisted of only
 2 individual habitat patches (acrylic boxes) and there were 5 replicate
 landscapes for each temperature treatment (for a total of fifteen 2-patch
 landscapes). These landscapes were maintained in the same incubators as
 the landscapes used in the main experiment. To initiate this assay, we
 introduced 10 adults into the first patch in each landscape, where they
 were allowed three weeks to acclimate and form tunnels. Acetate strips
 were removed for 12 hours to permit dispersal into patch 2. Upon
 completion of the 12-hour dispersal period, adult beetles were censused in
 each patch. Only one 3-week (21 day) cycle was completed to prevent
 population growth, as it takes between 35 and 62 days for <em>T.
 castaneum</em> to complete its life cycle on this flour medium and
 across our three experimental temperatures (unpublished data). This assay
 thus removed the possibility of population growth, allowing us to isolate
 the direct effect of temperature on dispersal rate.
 <strong>Population growth rate
 assay</strong> To determine the direct effect of
 temperature on intrinsic population growth rates (r), we conducted a
 separate experiment in isolated populations (i.e., no movement across
 habitat patches). For this experiment, we used the three temperatures and
 the same flour medium as described above, and had three replicate
 populations per temperature. To initiate the experiment, we added 15 adult
 <em>T. castaneum</em> to 10 grams in a lidded plastic
 container. We then allowed populations to grow and expand and counted all
 live and dead adult beetles in each population every two weeks for 22
 weeks. After each count, we added an additional 5 grams of the appropriate
 flour type in order to provide a continuous supply of fresh
 resources.
description: # Data for: The effect of temperature on the rate of range expansion
 Dataset DOI: [10.5061/dryad.gf1vhhn0v](10.5061/dryad.gf1vhhn0v) ##
 Description of the data and file structure There is one included
 spreadsheet, Breslin_and_Grainger_Dryad_Data.xlsx, that contains all data.
 A sheet called 'metadata' gives variable definitions to all
 three other sheets. | main\_experiment | 
 
 | | :---------------------- |
 :--------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | column | explanation | | count | count number (counts were conducted every three weeks for 18 weeks) | | temperature | temperature in degrees celcius | | replicate\_number | replicates linear lanscapes (10 per temperature treatment) | | patch\_number | patch number in linear experimental landscapes (4 patches were added after the first survey, so there are patches 1-8 in first survey and patches 1-12 in subsequent counts) | | alive | number of live adult beetles | | dead | number of dead adult beetles | | 
 
 | 
 
 | | **movement\_assay** | 
 
 | | column | explanation | | temperature | temperature in degrees celcius
 | | replicate\_number | replicate two patch lanscapes (5 per temperature
 treatment) | | patch\_number | patch number in two-patch experimental
 landscapes | | alive | number of live adult beetles | | dead | number of
 dead adult beetles | | 
 
 | 
 
 | | **growth\_rate\_assay** | 
 
 | | column | explanation | | count | count number (counts were conducted
 every two weeks for 22 weeks) | | temperature | temperature in degrees
 celcius | | alive | number of live adult beetles | | dead | number of dead
 adult beetles |