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Todd Pierson

Experiment: Climate change and invasions

Treefrog movement and assembly

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Background:

Amphibians in the southeastern USA
Stratification across vertical gradient

Water resources
Species interactions

Cuban treefrog invasion
Climate-induced water limitation

Green treefrog

Squirrel treefrog

New York Times

Variability in water resources

Frog species richness

Cuban Treefrog

The southeast has the highest frog diversity in north America—with conditions in the coastal plains being particularly favorable
There are two known to co-occur throughout the coastal plain: green & squirrel treefrogs
These are both pond-breeding amphibians who need standing water to reproduce, but they also moist habitat it in the uplands – affected by water resources
In the uplands, you’ll find that these animals tend to occupy different vertical heights in the forest, depending on the time, season, or conditions
This is because treefrogs stratify themselves vertically depending on the availability of moist microhabitats and avoiding interactions with other species…
These interactions can be especially important due to Cuban treefrogs, steadily making it’s way through Florida since the 70s
They are known to predate and compete with natives, to the extent of causing local extinctions, but there is another issue
The reason Cubans have spread here is due to climate change—which is expected to cause water resources to become more variable

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How will this affect community assembly?
Environmental filtering:

Regional: water resource limitation
Local: antagonistic interactions

Could dehydration exacerbate interactions?

Background: Community impacts

Spatial Scale

Abiotic:

Biotic

Species pool

Local communities

Climate change

Invasive species

New York Times

Variability in water resources

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Extrinsic factors:

Vertical enclosure experiment:

Biotic treatment: species pairings
Abiotic treatment: water availability

Intrinsic factors:

Physiological experiment:

Wind tunnel (dehydration)
Soaking bath (rehydration)

Behavioral experiment:

Watering conservation posturing

Methods: Experimental design

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Methods: Experimental design

ABIOTIC TREATMENT

Displacement

Full Low High

Green treefrogs

Cuban treefrogs

Squirrel treefrogs

Baseline vertical niche

Baecher, JA, et al. 2023. J. of Anim. Ecol.

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Methods: Experimental design

Avoidance

Green treefrogs

Cuban treefrogs

Squirrel treefrogs

BIOTIC TREATMENT

Baecher, JA, et al. 2023. J. of Anim. Ecol.

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Methods: Analysis

Physiology & behavior:

Filters:

Error term:

Base model:

Fully interactive model

Model set:

Baecher, JA, et al. 2023. J. of Anim. Ecol.

Now I’ll show you the modeling design, which I would normally breeze over, but this part took a while for me to figure out how it should work!
So we have our response variables—displacement and avoidance—and our covariates—each which represent different processes from the experiment.
The intrinsic factors—behavior and physiology, and the extrinsic factors—both experimental treatments.
So, I’ll outline the full global model used here for the displacement response variable, which is scaled and centered and fit as a normal distribution.
These data are temporally replicated across 6 timesteps and across 63 individual frogs.
Here is the base model, which includes some of the basic background information of the experiment—we have random slopes and intercepts for each indvidual frog (to deal with the non-dependence over time and species), we have an over all intercept (fixed at zero because they actually start off a the center of the perch, which is at 0), and we have some basic fixed effects for experimental conditions (like temp, humidity, a code for how they are placed on the refugia).
Next we have the experimental model—which includes fixed categorical covariates for the focal species identity, the species pair (if any), and the abiotic treatment.
The intrinsic model, which includes all of our physiological / behavioral covariates as fixed effects.
And finally, the error model, which I was noticing some residual autocorrelation due to the sampling design, so I used autoregressive structures in the error term. Here an ARIMA, but with avoidance, a moving average ARMA.

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Results: Displacement

Displacement

Baecher, JA, et al. 2023. J. of Anim. Ecol.

Finally we have the results! It was very difficult to visualize all 27 treatments, but let me break it down.
Here is the results from just the green treefrogs. The focal species is indicated on the right-side tabs, while the paired species is on the x-axis!
So when the focal species and paired species are equal, this is a null biotic level (indicated with dashes).
Here the asterisks are comparing displacement between the full water treatment and the low and high manipulations
We see here green treefrogs showed significant shifts in their vertical niche to track the water limitations.
Next we can see that those vertical niches were also affected by the paired species, attenuating the green treefrogs ability to climb while tracking water resources.
If you squint, you’ll notice the two native species have a zig-zag pattern, with the Cuban showing the strongest and with the null biotic treatments have the strongest amplitude!
So we’re seeing early signs of the interactions between biotic and abiotic treatments
But the Cuban treefrogs are a different phenomenon, not exactly showing the same patterns.

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Results: Avoidance

Avoidance

Baecher, JA, et al. 2023. J. of Anim. Ecol.

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Results: Climbing behaviors

Directional syndromes

Baecher, JA, et al. 2023. J. of Anim. Ecol.

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Results: Directional syndromes

Baecher, JA, et al. 2023. J. of Anim. Ecol.

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Results: Biotic-abiotic interactions

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Local Regional Global

Biotic:

Abiotic:

Strength of processes

Pearson and Dawson 2003

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Discussion: Biotic-abiotic interactions

Scale-dependent filters

Abiotic factors: broad range limits (Kraft et al., 2015)
Biotic factors: local occurrences (Soberon, 2010)

Filtering mechanisms are:

Ordered
Non-interactive
Inherently filtering

Belyea & Lancaster, 1999; Keddy, 1992; Götzenberger et al., 2012