Eric R. Larson

@ericrlarson.bsky.social

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Associate professor in freshwater ecology, University of Illinois at Urbana-Champaign. Crayfish, invasive species, environmental DNA, and more. https://publish.illinois.edu/erlarson/

Two researchers sample a shallow, rocky stream with D-frame nets for invertebrates
Wide, blue river passes under a tall concrete arch bridge
Roughly a dozen conference attendence standing on a stage before a project screen, from left to right: Matt Barnes (Texas Tech), Lindsey Reisinger (University of Florida), Eric Larson (University of Illinois), John Drake (University of Georgia), Bill Perry (University of Minnesota Duluth), David Lodge (Cornell), Romi Burks (Southwestern University), Kristy Deiner (Simplex DNA), Kara Andres (Illinois State University), Jon Bossenbroek (University of Toledo), Reuben Keller (Loyola University Chicago), Andy Mahon (Central Michigan University), and Chris Jerde (University of California Santa Barbara)
"Look. It's a metaphor. They wrote about a lot of other stuff."
Brock Sampson to H.E.L.P.eR: "Yes, and hobbits, too."
A four panel (2 x 2) image of streams in northern Alabama with bedrock banks and forested riparian zones
Idaho versus Boise State football series results from Wikipedia at https://en.wikipedia.org/wiki/Boise_State%E2%80%93Idaho_football_rivalry
Aschhoff said he's completed around 2,000 dives in various areas of Okanagan Lake over the last 14 years and has never seen a crayfish before. As the crustacean tend to live in rocky areas, they are usually found closer to shore.
Three stream sites as columns over five sampling events as rows from fall (top) through mid-winter (bottom), taken from bridge crossings looking upstream. The stream in the left column is adjoined primarily by row crop fields with a wood lot in the distance. The stream in the middle column has an intact riparian buffer with leaves changing color at the top rows through absent in the bottom rows. The stream in the right column is the largest and is neighbored by dense riparian forest with a ridgeline visible in the middle distance.
Linear mixed model predictions for aquatic (blue solid) and terrestrial taxa richness (brown dotted) in response to (A) rainfall (in centimeters) and (B) water temperature (in degrees Celsius) with 95% CIs.
A black and white image of a signal crayfish (Pacifastacus leniusculus) seen from the side or lateral view with barnacles covering ~50% of its carapace.
A red covered bridge over a river in winter with shallow snow on both banks and thin, clear ice covering most of the surface of the water
Two crayfish burrows seen from above or plan view
A wadeable, second order stream in downstate Illinois that has recently had all riparian vegtation removed from one bank, where three researchers stand looking at the stream. The opposing bank retains a small block of forest in early spring, with invasive honeysuckle beginning to leaf out. A row crop field is visible in the middle distance below a blue sky with scattered clouds.
A figure showing a stream without a forested riparian buffer in the top panel and a stream with a forested riparian buffer in the bottom panel. A cartoon water bottle with a DNA symbol in each water bottle directs to adjacent insets with silouttes of representative wildlife at each stream, with the forested stream having more species and including amphibians, reptiles, bats, and flying squirrels.
An irrigation ditch centered in the image that has dried to a single, isolated pool in the foreground. There are grassy banks on either side of the ditch, with two men standing on the right bank in an orange sweatshirt and blue shirt.
A prairie with a wetland in the middle distance and a tree line on the horizon under low, scattered clouds
A slightly out of focus rusty crayfish (Faxonius rusticus) held between a thumb and forefinger with the calm surface of a lake in the background
An olive brown crayfish held between a thumb and finger with a drying stream pool out of focus in the background.
A drying stream pool above a culvert, with a researcher collecting crayfish traps. Five gallon buckets, crayfish traps, and a clipboard are visible on the stream bank.
An isolated stream pool above a culvert (not visible, where the photographer is standing) with a dry bed upstream. The pool is turbid and surrounded by dry steppe, with mountains visible in the distance under a mostly sunny sky.
Two researchers hold a seine downstream of them in a moderately wide, rocky river
A pile of debris on grass that features many obvious crayfish claws and carapaces, cleared from a filter on center pivot irrigation that had clogged
A map from the United States Geological Survey's nonindigenous aquatic species database showing the native range of the virile crayfish (Faxonius virilis) as light brown and non-native watersheds as a dark red. The species has a broad native range spanning the Great Plains, upper Mississippi River, and Great Lakes basin, but now occurs as a non-native species west of the continental divide and in Atlantic-draining watersheds of Appalachia. It's probably the most widespread non-native crayfish in North America, but is minimally studied relative to invasive crayfishes with more global distributions like the red swamp crayfish (Procambarus clarkii).
An irrigation diversion with sloughing banks that, on closer inspection, were full of crayfish burrows. Mountains and patchy clouds are visible in the background behind dense grass.
A cat door-sized panel in a water control structure or dam that is partially open but clogged with debris, letting out a small flow of water.
An irrigation diversion in an arid landscape backing up water behind it, with a shallow, rocky stream below. The diversion consists of a series of concrete retaining walls and metal water controls that can be raised or lowered.
A pilose crayfish (Pacifastacus gambelii) held close to the camera with a five gallon bucket and clipboard out of focus in the background on a grassy river bank. The pilose crayfish is mottled olive brown and yellow, with distinctive strips of hair on the lateral, dorsal surface of its visible claw.
The manuscript title "Predicting potential distributions of freshwater invasive species in novel environments" above the author Eric R. Larson and an affiliation at the University of Illinois, with a conceptual figure illustrating the transfer of invasion risk information from a widely distributed to an emerging, prospective invasive species. The figure's caption from the paper reads "Researchers might borrow information from supraspecific modeling units, sometimes termed avatar species or surrogate species, to make precautionary habitat suitability estimates for species under evaluation as prospective invaders that lack nonnative occurrence records. The simple example here uses BioClim bounding boxes (Busby 1991) on only 2 predictor variables to quantify underestimation of abiotic tolerances for a widely distributed invader when using only native-range occurrences relative to a total model that incorporates nonnative occurrences (A). The magnitude of this underestimation can be transferred to a species with only native-range occurrence data under evaluation as a prospective invasive species (B). Transferring this information may need to account for asymmetrical shifts in abiotic tolerances or changes in the direction of relationships between multiple predictor variables (Larson et al. 2014) and might also use the supraspecific modeling unit to identify total range-informed thresholds of habitat suitability for transfer (Liu et al. 2005)."
Water plunging over a small concrete wall into a downstream, rocky river shot at a low angle to the stream, with a riparian forest of willows and aspen in background below a partly cloudy sky.
A researcher in chest waders holding a measuring tape and clipboard standing in a shallow, rocky river downstream of a concrete water control structure that is at grade with both the upstream and downstream bed of the river. The water control structure might be slippery or hard to walk across for a crayfish, but current velocity was too low to exceed the swimming ability of crayfish.
A view across a river channel centered on a small concrete dam or water control structure, which extends into the riparian zone and has a noticeable drop or plunge at its downstream end. The river is shallower and rocky below the dam and deeper above.
A latrine pile of crayfish fragments with a low gradient river in the background
A two panel figure cropped from a scientific journal article, where the left panel (C) shows a crayfish barrier extending across a spring system as a stainless steel wall; you can't tell from this image that the barrier is submersed but using the high rate of water flow from right to left to exclude crayfish from swimming over the barrier. The right panel (D) shows a more vertical drop barrier where stainless steel walls adjoin a high-velocity spillway with about a half foot drop downstream. This would likely be fish passable (can jump from the downstream plunge pool) but not crayfish passable.
Road crossing a stream above a concrete slab with a 2-3 foot drop above a downstream pool. The stream is not flowing and clumps of algae are visible in the standing water. A crayfish trap is visible in the bottom left corner.
A relatively fresh (non-stinky) crayfish mortality in-hand with a rocky lake beach in the background
A crayfish gastrolith or stomach stone, as a small white circle of mineral, held in a human hand above a stream in the background
A row of seven large crayfish claws and one carapace with both claws against a rocky shoreline. The claws all share the diagnostic hairy patches of the pilose crayfish (Pacifastacus gambelii).
Fragments of crayfish, including a partial carapace, claws tips, and small, white stomach stones or gadtroliths, on a background of green algae on a river bank. This was directly in front of a deep den or burrow of a mammal predator into the bank (outside of the image).
A crayfish claw with hairy patches on the left and right dorsal surface, with an out of focus lake in the background
Irrigation diversion with spillway, two culverts, and a rocky fish passage channel in the distance with dry mountains in the far background. It's warm and windy. We're acclimating from a heavier atmosphere in Illinois. We'll survive.
The pilose crayfish (Pacifastacus gambelli), a mottled crayfish with patches of dense hairs on the dorsal surface of its claws. It's native to the upper Snake River and Bonneville Basin watersheds of Idaho, Nevada, Utah, and Wyoming, awfully hard to find, and largely replaced from its historic occurrences by the non-native virile crayfish.
A map of the historical extent of the tallgrass prairie (gray) and 319 sampled remnants (black circles) in RELIX across the Midwestern United States. 34 remnants are not shown on the map since they did not have precise location information.
A four panel figure showing (a) a biologist wading in a turbid river with a water sample, (b) a real-time or quantitative PCR amplification plot with a positive environmental DNA detection, (c) a biologist searching concrete riprap on a river bank, and (d) two freshwater mussels that have been marked for future monitoring and recapture.
A large boulder seen underwater across the width of a stream, covered in dark spots that are crayfish out foraging during the day.
Cascading stream in shade within a steep, rocky canyon.
Manatee emerging from shallow water, viewed from above
San Juan convention center, a large, glass building with a wave-shaped overhang taken from across a reflecting pool
Map of the contiguous United States showing "crawfish" prevalent as terminology in the south and especially Louisiana, "crayfish" in the northeast and upper Midwest, and "crawdad" in the Ozarks / southern Great Plains / northern California and Oregon.
A Pacifastacus crayfish from the Olympic Peninsula of Washington State - brown/red with moderately long claws
Dr. Nisikawa Usio in rain gear with several wire mesh crayfish traps on the shores of Lake Mashu, a crater or caldera lake in Hokkaido, Japan. The lake sides are steep, forested cliffs and conditions are slightly foggy. The lake is only open to researchers as a former fisheries experimental station (the Signal Crayfish was first stocked here in Japan in the 1920s, but didn't spread widely until after the 1980s), and was accessible by a series of rope ladders down the cliff faces. This was my first day in the field in Japan, and it started with our undergraduate technician taking a minor fall and injuring his leg - we weren't sure how severely. After gingerly climbing back out of the old volcano, we drove to the nearest rural medical center, where the injury was diagnosed as an ankle sprain. We returned to our minshuku and recovered over beers, and had better luck for the next five weeks of work.
The Okanagan Crayfish: a dark red crayfish extending a large claw towards the camera
Orange and blue sunrise behind a calm river in early spring, with Sycamore roots in the foreground
Red covered bridge over an icy river with only about 10% of the channel open and flowing
A bright red covered bridge crosses a partially frozen river with bare trees in the riparian zone below a mostly sunny sky.
A white bucket containing about 20 rusty crayfish (Faxonius rusticus), an olive brown crayfish species with a rust red spot on each side of the carapace.
The cover of "Alien Animals in British Columbia" by G.C. Carl and C.J. Guiguot from the British Columbia Provincial Museum, Victoria, Canada featuring a Virginia opossum carrying three young.
Conceptual model of environmental DNA sampling and life history events expected to correlate with peak environmental DNA detections, showing four species and eDNA detectability over five sampling events from ice off through early, mid, and late summer to ice on in lakes. Spiny waterflea detections should peak when they reach peak abundance and hatch in late summer. Common carp detections should peak between ice-off and early summer when carp spawn. Zebra mussel detections should peak near mid-summer when they release veligers. Rusty crayfish detections should peak in the summer or early autumn due to moults or ovigery. Icons of the four species by the Minnesota Department of Natural Resources.