Eric R. Larson

A prairie with a wetland in the middle distance and a tree line on the horizon under low, scattered clouds

New faculty position in the University of Illinois Department of Natural Resources and Environmental Sciences for an assistant or associate professor of agroecology: illinois.csod.com/ux/ats/caree.... Position closes October 31st. Happy to answer questions about the dept / university / town.

ecoevojobs.net 2025-26

UPDATE: The 2025-2026 list of faculty and postdoc positions in ecology and evolutionary biology is out! Be sure to check out this active and helpful community run resources! docs.google.com/spreadsheets...

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

Two boats docked in the foreground of a large lake with a yellow floating platform in the middle distance and a forested shoreline ~2 miles back on the horizon

Sunset on a large, calm lake as a band of orange below emerging stars

A square white bucket with ~16-20 rusty crayfish (Faxonius rusticus) waiting to be counted and measured

Completed my annual trip to northern Wisconsin, continuing population monitoring of invasive rusty crayfish (Faxonius rusticus) that extends back to the 1970s. Populations remain down, at only ~25% of past peak abundances, with surprising catches of large native snails in our traps.

It was a real pleasure to participate in the Mazama Newt Workshop at Crater Lake hosted by the @oregonzoo.bsky.social and the National Park Service. Discussions focused on a recovery plan for the Mazama newt in light of an exploding invasive signal crayfish. Great to see @ericrlarson.bsky.social!

New database catalogs plant species in latest effort to restore prairies The RELIX catalogues every plant species in 353 prairie remnants — parts of the native grasslands of the midwest that were not converted to farmland during colonization.

The RELIX catalogues every plant species in 353 prairie remnants — parts of the native grasslands of the Midwest that were not converted to farmland during colonization.

An olive brown crayfish held between a thumb and finger with a drying stream pool out of focus in the background.

A small but rocky stream below a blue sky, flowing through sagebrush steppe.

A view from a bridge crossing down into a stream bed of cobble and fine sediments, where one crayfish is visible crawling on a rock.

This pool was packed with non-native virile crayfish; we recovered >120 in only four traps. It will likely dry out by the end of summer, but virile crayfish have dispersed through this intermittent reach. We found them abundant in the permanent stream higher up the watershed (photos 2 & 3).

This is a good prediction.

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.

So ... any crayfish in this small and declining habitat?

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.

Our search for invasive crayfish barriers includes more than just dams or irrigation diversions. Because the virile crayfish is intolerant of stream drying (doi.org/10.1086/725318), intermittent reaches could present barriers to upstream spread to permanent streams in the mountains.

They always are, from Australia to Madagascar to Canada

Two researchers hold a seine downstream of them in a moderately wide, rocky river

Two researchers check hand nets while overturning rocks on the shoreline of a reservoir

Two researchers check dip nets along the shore of a stream impounded behind an irrigation diversion

Crayfishing.

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

Here an abundance of crayfish claws and carapaces have been cleaned out of center pivot irrigation filters that had clogged. In our study region, many farmers and ranchers identify this as a problem, but I don't think anyone has quantified these type of impacts of invasive crayfish to agriculture.

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).

The non-native virile crayfish (Faxonius virilis) in particular has boomed in regions of the western US without any native crayfishes like the Colorado River (nas.er.usgs.gov/queries/Fact...). Given its abundance in irrigated lands, I wonder if we're missing damages and costs as an ag pest?

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.

I routinely get calls from water management districts in southern Idaho concerned about damage to canals from burrowing by this same non-native crayfish. In estimates of economic costs of invasive crayfish (doi.org/10.1016/j.sc...), I think we're missing effects on agriculture in the western US.

The manager at this property noted they have problems with the invasive crayfish clogging irrigation infrastructure downstream of the diversion. Economic damages to agriculture from invasive crayfish are well-known on other continents, but I wonder if we've missed an impact in the arid western US.

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.

A close-up of a small panel or gate in a water control structure that is clogged with both aquatic plant debris and noticeable crayfish carcasses, including visible walking legs and abdomens

This was another barrier where non-native crayfish passage was obvious before we started sampling. Here a small gate in one of the water control structures was clogged with carcasses from the upstream pool. I think this barrier is open to flow at times of the year when crayfish are moving around.

Disturbance and species displacement: different tolerances to stream drying and desiccation in a native and an invasive crayfish 1. Crayfish are among the most threatened taxa in the world and invasive crayfish are the primary cause of the decline of native crayfish. Most research has emphasised biotic interactions as the mech...

Crayfish in the genus Faxonius (formerly Orconectes) differ enormously in their desiccation tolerance (e.g., doi.org/10.1111/j.13...). Terrestrial locomotion by crayfish also requires moderate temps w/high humidity (www.jstor.org/stable/1549337). That's rare in our study region in the summer.

Winners and losers over a ½ century of change in crayfish assemblages of Wyoming, USA | Freshwater Science: Vol 42, No 2 Abstract Crayfish have experienced extensive assemblage reorganization as a result of global change, with some species becoming globally invasive and others becoming rare or extinct. We combined histo...

However, the invasive crayfish we're working with is really intolerant of desiccation. Faxonius virilis is usually excluded from intermittent or ephemeral habitats by other species (doi.org/10.1086/725318). I think it's going to be reluctant to go over-land in this very arid region.

Yeah, good (and intentional) crayfish barriers extend into the riparian zone to prevent passage overland (bsky.app/profile/eric...). We're trying to do some quick characterization of these prospective barriers - which includes extension into the riparian zone, how steep or climbable banks are, etc.

We're visiting so many potential barriers, of so many barrier types, that it's been our intent to work backwards. If we find crayfish below but not above a prospective barrier, we'd then ask "why?" - how is e.g. this diversion being operated differently than others in the watershed?

The crayfish would probably have a hard (perhaps not impossible) time moving around at low temps and high discharge in winter and spring. But if you opened the gates in the fall - easier to work than winter? - there would probably be a good window for crayfish to move upstream.

This is a snow melt-dominated flow regime with really high discharge in the late spring and early summer. I've wondered if you want the gates generally open winter and spring to not blow out your infrastructure, then closed in the summer at low flows when you're using the water.

This work is in the Bear River watershed of Wyoming/Utah/Idaho. Here we're south of Evanston, Wyoming in a small tributary to the Bear. When would you wager (as a season or month) that the gates are likely to be open?

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.

This irrigation diversion looked promising as an invasive crayfish barrier. The diversion gates didn't appear to be climbable. Water is diverted into a buried pipe with screens to prevent fish entrainment. Concrete retaining walls extend into the riparian zone. Can crayfish get over or around this?

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.

A relief to add a new pilose crayfish site this week. This native species disappeared from the mainstem, low elevation Bear River in Wyoming between 1987 & 2007, replaced by the non-native virile crayfish (peerj.com/articles/5668/). Remnant populations are confined to higher elevation tributaries.

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)."

Freshwater invaders pose unique challenges to species distribution (or ecological niche) models used in risk analysis. New in Freshwater Science (doi.org/10.1086/737200), I identify strategies to improve predictions of suitable habitat for emerging, data-poor freshwater invaders using these tools.

The publications collected in this month's LTER Network News really demonstrated the wide range of impactful research the LTER does. Here's the list:

mailchi.mp/lternet/lter...

Frontiers | Review of Dam Effects on Native and Invasive Crayfishes Illustrates Complex Choices for Conservation Planning Dams are among the most prevalent and extreme alterations humans have perpetrated on fluvial systems. The dramatic physical and biological changes caused by ...

There's no doubt that some barriers are impassable to crayfish (doi.org/10.3389/fevo...), but we don't have good rules about which barrier attributes (height, flow velocity, material, extension into riparian zone) exclude passage by crayfish like we do for some fish (e.g., doi.org/10.1002/rra....).

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.

One challenge in our work is that although considerable effort has been directed at fish passage and barriers in the study watershed, crayfish and fish differ in what barriers they can and can't pass (e.g., doi.org/10.1016/j.bi...).