Using long-term data to investigate temporal changes in non-native crayfish populations of northern Wisconsin lakes

Sawyer, Elle K

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https://hdl.handle.net/2142/120575 Copy

Description

Title

Using long-term data to investigate temporal changes in non-native crayfish populations of northern Wisconsin lakes

Author(s)

Sawyer, Elle K

Issue Date

2023-05-01

Director of Research (if dissertation) or Advisor (if thesis)

Larson, Eric

Committee Member(s)

• Fuller, Becky
• Parkos, Joseph
• Bell, Alison

Department of Study

School of Integrative Biology

Discipline

Ecol, Evol, Conservation Biol

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

M.S.

Degree Level

Thesis

Keyword(s)

• crayfish
• invasive species
• sleeper invader
• body size

Abstract

Northern Wisconsin lakes in Vilas County have been systematically monitored for crayfish for a half century. My thesis research used this long-term data to gain a better understanding of non-native crayfish populations within these lakes, ranging from the well-known rusty crayfish (Faxonius rusticus, Girard 1852) to the recently rediscovered calico crayfish (Faxonius immunis, Hagen 1870). Faxonius rusticus invaded this lake system in the 1960s and has since spread and caused a variety of well-studied impacts, including decreasing macrophytes, outcompeting native congeners, and overconsuming macroinvertebrate prey such as snails. Long-term monitoring has revealed that some F. rusticus populations have started to decline in this region. Preliminary research has also shown that F. rusticus populations might be experiencing body size declines. Long-term data on how invasive populations change over time could be crucial for understanding how to minimize or prevent impacts of future invasive species. By using long-term data, I was able to ask unique questions to better understand non-native crayfish populations in Vilas County lakes. In my first chapter, I investigate how body size has changed in F. rusticus populations over time. Body size is a fundamental trait that is linked to many other characteristics of an organism. Body size is also a useful trait in the study of rapid evolution, especially as invasive species have been shown to rapidly evolve in as little as 10 years. I compared body size in F. rusticus to three predictors: time, lake surface temperature, and relative abundance. In some organisms, temperature has been found to decrease body size through a variety of mechanisms such as dissolved oxygen depletion or increased metabolic demand. Further, relative abundance might link to decreased body size via density dependence. Alternatively, a variety of other mechanisms like phenotypic plasticity, adaptive evolution, or enemy accumulation lack data in my study system over time, but could be represented by time itself as a proxy variable. Further, it was important to include time due to its indirect relationship on my other two predictor variables. Due to the possibility of non-independence among my predictor variables, I used structural equation modeling to investigate the influence of the predictors on body size, as well as the influence of time on temperature and relative abundance. I found that body size declined significantly over time, but that temperature and relative abundance did not significantly affect F. rusticus body size. Faxonius rusticus body size declines could be caused by a variety of mechanisms. Faxonius rusticus is a successful invader in part because of its large body size and aggressive behavior compared to other crayfish species. Accordingly, F. rusticus outcompeted both native and non-native crayfish species in becoming the dominant crayfish in my study lakes. As such, it may have been advantageous for F. rusticus to be large early in its invasion, but the benefits of a large body size relative to its costs may have declined over time. Alternatively, F. rusticus could have accumulated enemies like pathogens or parasites over time that have led to a decrease in body size. Although I did not uncover the specific mechanism linking time to F. rusticus body size declines, these phenotypic changes may still be anticipated to reduce the ecological impacts and interaction strength of F. rusticus in northern Wisconsin lakes. Declines in F. rusticus abundance and body size may create opportunities for subsequent crayfish invaders in lakes of Vilas County, Wisconsin. This led to my second chapter where I investigated the possible “sleeper” invader, F. immunis. Sleeper invaders are non-native populations that experience long time-lags between establishment and subsequent spread and negative impacts. Sleeper invaders challenge the ability of managers to differentiate harmless non-native species from harmful invasive species. Faxonius immunis was rediscovered in Vilas County in 2020 after not having been documented in this region since the 1970s. I used mtDNA barcoding to confirm these crayfish were F. immunis and had not been misidentified as another crayfish species. Next, I investigated whether interference competition with F. rusticus may have prevented F. immunis spread over the past several decades by measuring agonistic interactions between the two crayfish species. I modeled differences in aggression between species while controlling for size and reproductive form. I found that F. rusticus were consistently dominant over F. immunis, suggesting that competition with a larger, established invasive species may have restricted past spread by F. immunis. As F. rusticus populations and body sizes continue to decline, F. immunis may have an opportunity to spread and have ecological impacts in lakes of northern Wisconsin.

Graduation Semester

2023-05

Type of Resource

Thesis

Copyright and License Information

Copyright 2023 Elle Sawyer

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