A window of opportunity: Subdominant predators can use suboptimal prey.

Kelly A Jackson,Jennifer A White,Joshua S Mccord

doi:10.1002/ece3.3139

Abstract

Introduced species have been linked to declines of native species through mechanisms including intraguild predation and exploitative competition. However, coexistence among species may be promoted by niche partitioning if native species can use resources that the invasive species cannot. Previous research has shown that some strains of the aphid Aphis craccivora are toxic to a competitively dominant invasive lady beetle, Harmonia axyridis. Our objective was to investigate whether these aphids might be an exploitable resource for other, subdominant, lady beetle species. We compared larval development rate, survival, and adult weight of five lady beetle species in no‐choice experiments with two different strains of A. craccivora, one of which is toxic to H. axyridis and one that is nontoxic. Two lady beetle species, Cycloneda munda and Coleomegilla maculata, were able to complete larval development when feeding on the aphid strain that is toxic to H. axyridis, experiencing only slight developmental delays relative to beetles feeding on the other aphid strain. One species, Coccinella septempunctata, also was able to complete larval development, but experienced a slight reduction in adult weight. The other two lady beetle species, Hippodamia convergens and Anatis labiculata, demonstrated generally low survivorship when consuming A. craccivora, regardless of aphid strain. All five species showed increased survival and/or development relative to H. axyridis on the “toxic” aphid strain. Our results suggest that this toxic trait may act as a narrow‐spectrum defense for the aphids, providing protection against only some lady beetle enemies. For other less‐susceptible lady beetles, these aphids have the potential to provide competitive release from the otherwise dominant H. axyridis.

Highlights

Competition often plays a large role in shaping community structure (Menge, 1976; Price & Kirkpatrick, 2009)
We evaluated the development and survival of five lady beetle species: Anatis labiculata, Coccinella septempunctata, Coleomegilla maculata, Cycloneda munda, and Hippodamia convergens
Coccinellid species varied in their ability to use L-strain A. craccivora

Summary

Introduction

Competition often plays a large role in shaping community structure (Menge, 1976; Price & Kirkpatrick, 2009). Species that are the most successful in securing food and habitat resources can establish themselves as dominant species, potentially excluding other species that are less adept (Fretwell, 1969; Goldberg, 1987) For these subdominant species, survival in a community becomes contingent on exploiting alternative resources that cannot or will not be utilized by the dominant species The multicolored Asian lady beetle, Harmonia axyridis, is a notably dominant invasive predator species (Roy et al, 2016) This beetle originated in Asia and has spread to at least 38 new countries since 1988 (Brown, Thomas et al, 2011). Native lady beetle populations and species diversity have been in decline (Harmon, Stephens, & Losey, 2007), and it is thought that H. axyridis has played a role in the decreasing biodiversity in some coccinellid communities (Bahlai, Colunga-Garcia, Gage, & Landis, 2015; Brown, Frost et al, 2011)

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