University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln Transactions of the Nebraska Academy of Sciences Nebraska Academy of Sciences and Affiliated Societies Winter 3-1-2018 Food habits of imperiled Plains Topminnow and diet overlap with invasive Western Mosquitofish in the Central Great Plains Joseph Thiessen University of Nebraska at Kearney, [email protected] Keith D. Koupal Nebraska Game and Parks Commission, [email protected] Casey W. Schoenebeck University of Nebraska at Kearney, [email protected] Julie J. Shaffer University of Nebraska, Kearney Follow this and additional works at: https://digitalcommons.unl.edu/tnas Part of the Population Biology Commons, and the Terrestrial and Aquatic Ecology Commons Thiessen, Joseph; Koupal, Keith D.; Schoenebeck, Casey W.; and Shaffer, Julie J., "Food habits of imperiled Plains Topminnow and diet overlap with invasive Western Mosquitofish in the Central Great Plains" (2018). Transactions of the Nebraska Academy of Sciences and Affiliated Societies. 513. https://digitalcommons.unl.edu/tnas/513 This Article is brought to you for free and open access by the Nebraska Academy of Sciences at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Transactions of the Nebraska Academy of Sciences and Affiliated Societies by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. Food habits of imperiled Plains Topminnow and diet overlap with invasive Western Mosquitofish in the Central Great Plains Joseph D. Thiessen,1,4 Keith D. Koupal,2 Casey W. Schoenebeck,1,3 and Julie J. Shaffer 1 1 Department of Biology, University of Nebraska at Kearney, Kearney, NE 68849 2 Nebraska Game and Parks Commission, Kearney Field Office, Kearney, NE 68847 3 Present address: Minnesota Department of Natural Resources, 23070 North Lakeshore Drive, Glenwood, MN 56334 4 Present address: Idaho Department of Fish and Game, 1414 E. Locust Lane, Nampa, ID 83686 Corresponding author: Joseph Thiessen ([email protected]) This work was supported by the Nebraska Natural Legacy Project under Grant T-88-1; University of Nebraska at Kearney, Biology Department under Grant 56-0510-0119-001. Abstract: Plains Topminnow (Fundulus sciadicus) populations have experienced large declines throughout the Central Great Plains, with Western Mosquitofish (Gambusia affinis) introductions suggested as a contributing factor. There are limited studies identifying the food habits of Plains Topminnow and the trophic interactions with Western Mosquitofish. This study sought to determine if a diet overlap exists between the Plains Topminnow and the introduced Western Mosquitofish by identifying the feeding habits of both species. We analyzed diets from lentic and lotic populations of Plains Topminnow captured in August and found lentic top- minnows employed a generalist diet while lotic topminnow selected for gastropods. Additionally, Western Mosquitofish diets from regionally proximate lotic and lentic populations also displayed a generalist diet consisting of benthic, littoral and terrestrial mac- roinvertebrates. The two species did not show overlapping diets based on Schoener’s Index. Therefore we suggest the introduced Western Mosquitofish do not likely impact Plains Topminnow populations through food resource competition. Keywords: diet overlap, Great Plains, imperiled, invasive species, mosquitofish, topminnow. doi: 10.13014/K2319T31 Introduction competition, predation, habitat loss, stream fragmenta- Plains Topminnow (Fundulus sciadicus) is endemic to tion, climate change, water quality, and stream dewater- the Central Great Plains and has experienced a decrease ing (Fischer and Paukert 2008; Pasbrig et al. 2012). Over in historic range and local abundance (Schumann et al. the last century, much of the Central Plains landscape has 2016). As a habitat specialist with the capability to move been converted from grasslands to agriculture (Samson great distances the Plains Topminnow was once common and Knopf 1994), causing reductions in stream habitat throughout the Great Plains (Schumann 2015a; Schumann and biologic diversity (Pringle 1988; Jenkins et al. 2003). et al. 2016). Recent studies report a 72 percent decline in Habitat alterations and fish stockings across the Plains distribution throughout the Plains Topminnow’s native have increased interactions with non-native competitors range, which includes both a northern and a southern and predators. Additionally, large-scale landscape alter- spatially separated disjunct populations (Pasbrig et al. ations have favored non-native generalist species, which 2012). Nebraska represents 67 percent of historical oc- decreased native fish populations, presumably from de- currence sites and is thought to be the central stronghold creased habitat diversity (Smith et al. 2014). Western Mos- of Plains Topminnow distribution; however, a 66 percent quitofish (Gambusia affinis) are among the generalist spe- decline in occurrence was reported (Pasbrig et al. 2012). cies encountered by Plains Topminnow populations and Nebraska currently list Plains Topminnow as a Tier 1 spe- are commonly found to dominate local fish assemblages cies of special concern with populations considered at risk in disturbed streams (Chapman and Warburton 2006). (NatureServe 2016). Western Mosquitofish are the most widely distrib- The decline in Plains Topminnow presence is likely uted fish in the World and are the subject of increased re- linked to a multitude of reasons. Factors hypothesized search for their impacts on native fishes. These fish were to limit Plains Topminnow persistence vary from species introduced in Nebraska for mosquito control starting in 2018 Transactions of the Nebraska Academy of Sciences 38, 1–9 1 Plains Topminnow Food Habits 1972 (Kaufmann and Lynch 1991). Western Mosquitofish Ideally, wild populations of Plains Topminnow would have been implicated in the reduction of other topmin- be used for this assessment, but the protected status of now species due to direct predation of larval fish, with Plains Topminnow precludes the sacrifice of wild speci- little supporting evidence for resource partitioning im- mens and therefore Plains Topminnow specimens from pacts (Minckley 1973; Meffe 1984; Goldsworthy and Bet- two Nebraska Game and Parks Commission broodstock toli 2006; Laha and Mattingly 2006; Sutton et al. 2012). locations were used. Additionally, cohabitated popula- In mesocosm experiments, Plains Topminnow experi- tions of Plains Topminnow and Western Mosquitofish enced 70% mortality in co-existence with Western Mos- would best identify resource partitioning but mingled quitofish, but other Fundulidae species survived (Haas populations are rare as mosquitofish have been sug- 2005, Schumann et al. 2015b). However, distinguishing gested to rapidly displace topminnow (Thiessen 2016). the impacts between cohabited wild Plains Topminnow Introducing Western Mosquitofish to Plains Topminnow and Western Mosquitofish populations is complicated by broodstock populations in an effort to create a cohabi- both the conservation status of Plains Topminnow and tated population were not considered in the interest of short temporal scale of co-habitation. maintaining a viable broodstock population. Therefore, Food selection and diet overlap between Plains Top- Western Mosquitofish were collected from similar aquatic minnow and cohabitate species have not been docu- systems within regional proximity of Plains Topminnow mented. Western Mosquitofish have a generalist diet broodstock populations. (Mansfield and Mcardle 1998) preventing them from be- A total of 30 Western Mosquitofish were collected ing an effective biological control agent of mosquito pop- from Blue Hole WMA (lentic) and 30 from Sandy Chan- ulations (Kumar and Hwang 2006). However, knowl- nel State Recreation Area (lotic) using DC pulsed back- edge of Plains Topminnow food habits remains limited pack electrofishing techniques from August to Septem- and represents a gap in ecological understanding (Best- ber 2015 (Schumann et al. 2015b). A total of 30 Plains gen 2014). Previous studies deduced from morphological Topminnow from Sac-Wilcox WMA (lentic) and 30 from characteristics, associated habitat use, and observed feed- Rock Creek Fish Hatchery (lotic) were collected using a ing behavior that Plains Topminnow are surface feeders 381mm tall, 3 paneled cloverleaf trap; with 6mm mesh that primarily feed on Ostracods, chironomidae, and occa- galvanized wire and 12mm openings August to Septem- sionally feed on Gastropods from the Genus Physa (Strib- ber 2015. Study specimens ranged in length from 58mm ley and Stasiak 1982; Rahel and Thel 2004; Haas 2005; to 73mm. All study specimens were preserved in 4:1 Bestgen 2014). Historic evidence from actual diet analysis ethanol:water solution immediately after capture. The of 12 specimens supported this hypothesized feeding be- entire digestive tract was removed from each fish and havior of surface insects (Ellis 1914), while a recent effort prey items were identified to order and quantified as fre- from the southern range of distribution found a more di- quency of occurrence. verse diet including greater utilization of benthic organ- Prey collection: Prey availability at Plains Topmin- isms (Thompson 2014). However, the diet contents from now collection sites was determined using samples of Missouri were from lentic specimens only and may be the both benthic and littoral macroinvertebrates. Preliminary