Consumption of a dangerous ant (Camponotus vicinus) by a threatened minnow (Notropis simus pecosensis).
Notropis simus pecosensis is listed as threatened by federal and state governments and is endemic to the Pecos River of New Mexico and Texas (Hoagstrom et al., 2008a). It typically occupies fluvial habitats of the mainstem Pecos River, which is characterized by a wide, sand-bed channel (Hatch et al., 1985; Propst, 1999; Hoagstrom et al., 2008b).
Opportunistic feeding on terrestrial invertebrates likely is important for N. s. pecosensis if periodic flash flooding makes them available. Drift feeding on terrestrial invertebrates (including ants) is widespread within Notropis (e.g., Reisen, 1973; Mendelson, 1975; Whitaker, 1977; McNeely, 1987; Bean et al., 2010). Starrett (1950) noted that three species of Notropis in the Des Moines River, Iowa, took terrestrial invertebrates during floods. Further, the streamlined morphology of N. s. pecosensis, its forward-facing mouth, raptorial pharyngeal teeth, and habitat associations suggest it feeds in fluvial habitats (Hubbs, 1941; Hatch et al., 1985; Bestgen and Platania, 1990; Hoagstrom et al., 2008a), most likely on drifting animals entrained within the column or on the surface of water. S. P. Platania (in litt.) surveyed 655 stomachs of N. s. pecosensis and listed, among other items, terrestrial invertebrates (including ants) and Bestgen and Platania (1990) reported terrestrial invertebrates in 6 of 15 stomachs examined from the extinct Rio Grande bluntnose shiner (Notropis simus simus).
Many species of North American Camponotus are polymorphic and their major-workers and queens are the largest ants in western North America (Wheeler and Wheeler, 1986). Camponotus vicinus is distributed widely in New Mexico, where it favors sandy and rocky soils (such as those near our collecting locality) and sometimes occupies riparian habitats (Milford, 1999; Ellis et al., 2002; MacKay and Mackay, 2002). Although ground nesters, C. vicinus commonly tends homopteran larvae (i.e., aphids) on vegetation (MacKay and MacKay, 2002). Thus, workers can fall into the river from overhanging plants and can be entrained by floods.
We presume the ant locked onto the jaw and, by filling the mouth of the shiner, could have led to death of the shiner, but the shiner appeared to be in good health at time of capture. locking onto potential predators is a stereotypical behavior of ants exhibited in the context of defense of colonies. For example, lucas and Brockmann (1981) studied the predatory behavior of antlions (Myrmeleon crudelis) they fed red-imported fire ants (Solenopsis invicta) and, in two cases, antlion larvae died with fire ants locked onto their mandibles. Lucas and Brockmann (1981) speculated that the antlions died because attached ants disrupted normal pit-building behavior and they estimated that [less than or equal to] 20% of antlion larvae might suffer this fate.
It appears that either N. s. pecosensis normally prevails over ants as prey or large major-worker ants rarely are encountered. Avoidance of flooded riparian areas in the Rio Grande of New Mexico (Milford, 1999) and tolerance for relatively dry habitats (Mankowski and Morrell, 2011) suggest that C. vicinus may avoid habitats typically inundated by floods. In general, floods are catastrophic for ground-nesting ants and Camponotus is rare in habitats with high frequency of flooding (Ballinger et al., 2007). We collected the shiner at a site with high banks that preclude inundation of the floodplain during typical flooding events. However, riparian trees and shrubs overhang the river from the banks. Hence, it seems most likely the ant fell into the river from overhanging vegetation. Cadwallader et al. (1980) reported that sites in the Murray-Darling Basin, Australia, with overhanging vegetation contributed more terrestrial invertebrates to diet of fish than areas without overhanging vegetation, and that larger fish ate more terrestrial organisms than smaller fish. The 59-mm shiner we collected is large for this species (Hoagstrom et al., 2008b).
Predators take a risk when they attack prey that is well armed or relatively large. Specialized predators tend to circumvent the defenses of target prey (e.g., Wignall and Taylor, 2009) and predators that specialize on eating ants have strategies and behaviors that reduce their risk (e.g., Lucas and Brockmann, 1981; Allison and Cepeda, 2009). Thus, it is possible that N. s. pecosensis rarely encounters major-workers of C. vicinus and its typical attack behavior is poorly suited to subdue such prey, or it could be that the individual shiner described herein unsuccessfully took a risk for a potentially rewarding meal.
The United States Bureau of Reclamation contract 04AA402212 provided funding for collecting fish. We thank S. D. Blocker and E. I. Gilbert for assistance in the field, R. A. Meyers for photography and composition of the figure, and I. Asensio-Sierra for translation of the abstract to Spanish.
Submitted 26 September 2011. Accepted 28 November 2012. Associate Editor was Robert J. Edwards.
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Stephen R. Davenport, * John F. Mull, and Christopher W. Hoagstrom
United States Fish and Wildlife Service, New Mexico Fish and Wildlife Conservation Office, 3800 Commons NE, Albuquerque, NM 87109 (SRD)
Department of Zoology, Weber State University, 2505 University Circle, Ogden, UT 84408 (JFM, CWH)
* Correspondent: Stephen_Davenport@fws.gov
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|Author:||Davenport, Stephen R.; Mull, John F.; Hoagstrom, Christopher W.|
|Date:||Mar 1, 2013|
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