Presence and management of the invasive plant Gypsophila paniculata (baby’s breath) on sand dunes alters arthropod abundance and community structure

Highlights

• We examined shifts in arthropod communities due to management of an invasive species.

• Invaded plots had double the total numbers of arthropods than reference plots.

• Sap-feeding herbivores, pollinators, and predators were abundant in invaded plots.

• Minor shifts in arthropod family composition occurred with management.

Abstract

Invasive alien plants represent a global threat to biodiversity at multiple trophic levels, including arthropod communities which represent an important group of organisms in any ecosystem. Because of complex interactions among organisms, it becomes important when managing invasive plant species to consider impacts of both the invasion and management efforts on arthropods. In this study, we examined shifts in arthropod communities relative to invasion and management of Gypsophila paniculata (baby’s breath), an invader of sand dune systems in Michigan, USA. We compared arthropod abundance and diversity for multiple trophic levels and functional guilds in invaded, managed, and reference plots from 2007 to 2010. Invaded plots had almost double the total numbers of arthropods and 20% more families than the reference and managed plots in 2008–2009. This was beyond a simple biomass effect due to the invasive plant. G. paniculata presence was also associated with an increase in sap-feeding herbivore abundance and dominance, increased pollinator and predator abundance, and increased family diversity in Hemiptera and Hymenoptera. There was no strong effect of management on arthropod communities, though a canonical analysis of principal coordinates indicated that reference and invaded plots were characterized by different families of arthropods. The consequences of these changes for the native plant community are unknown, and more mechanistic understandings of changes in biodiversity of higher trophic levels due to invasion and management are needed.

Introduction

Invasive alien plants represent a global threat to biodiversity at multiple trophic levels (Levine et al., 2003). In general, invasive alien plants are known to reduce both plant and animal diversity (Vila et al., 2011), though the responses of different functional groups of organisms to invading plants are less understood. The studies that have examined functional group responses to invasion often only focus on key groups such as pollinators (e.g., Hanula and Horn, 2011, Lindsay et al., 2011), or have conflicting results. For example, invasive plants can have both positive and negative effects on pollinators (Bartomeus et al., 2008). Restoration efforts often involve removal of invasive plants, and it becomes important to consider responses of organisms at multiple trophic levels when evaluating restoration effectiveness from a biodiversity perspective, though this is rarely done (Heleno et al., 2010, Reid et al., 2009).

Arthropods represent an important group of organisms in any ecosystem, often connecting primary producers with higher trophic levels of animals. Invasive plants can impact arthropod communities indirectly by reducing plant species richness (Gerber et al., 2008, Toft et al., 2001), or directly by altering habitat structure and food availability such as nectar (Chittka and Schurkens, 2001). These changes could further stress native plants through mechanisms of apparent competition, resulting in an “invasion ratchet” (Orrock et al., 2010). Changes in arthropod communities could also alter ecosystem traits such as nutrient cycling through feedbacks with the plant community (Whiles and Charlton, 2006).

Because of complex interactions among organisms, it becomes important when managing invasive plant species to consider impacts of both the invasion as well as management efforts on arthropod communities. For example, many native plants need pollinators for successful reproduction. Removal of Ligustrum sinense in Georgia increased native bee diversity, a desirable restoration outcome (Hanula and Horn, 2011). However, other studies have shown that invasive plants can increase pollinator activity on native plants through facilitation (e.g., Woods et al., 2012). Herbivory on native plants can also be reduced in the presence of unpalatable invasive species through a shared defense mechanism (Atwater et al., 2011) or associational resistance (Tahvanainen and Root, 1972), while herbivory might actually increase on natives in the presence of palatable invasives through mechanisms of associational susceptibility (White and Whitham, 2000).

In this study, we examined shifts in arthropod communities relative to the presence and management of Gypsophila paniculata (baby’s breath), an invader of sand dune systems in northwest Michigan. Great Lakes sand dunes represent the most extensive freshwater dunes in the world, covering over 1000 km² in Michigan alone (Albert, 2000). As a primary successional habitat, plant diversity is characteristically low, however a number of endemic species such as Pitcher’s thistle (Cirsium pitcheri), Houghton’s goldenrod (Solidago houghtonii), and Lake Huron Locust (Trimerotropis huroniana) are present, and these dunes represent a unique flora and fauna. G. paniculata, a forb native to Eurasia, was introduced to North America as an ornamental in the late 1800s (Darwent and Coupland, 1966), is listed as a noxious weed in Canada, California, and Washington where it invades sandy agricultural fields, and is considered to be one of two high-priority species threatening dune habitats by the Great Lakes National Park Service Biological Resource Management Division. It is believed that invasion in Michigan initiated near Point Betsie (44°41′08″N, 86°15′11″W) in the northwestern Lower Peninsula of Michigan in the early 1900s, and has been dispersed primarily to the northeast by prevailing winds to invade other open dune sites along a 260 km stretch of shoreline (Kleitch, 2009). In some dune areas, G. paniculata comprises 80% of all vegetation (Karamanski, 2000). It is believed that G. paniculata creates problems for the dunes by over-stabilizing a typically wind-disturbance driven habitat, and may be capable of out-competing native dominant grass species (e.g., Schizachyrium scoparium and Ammophila breviligulata) for resources (Darwent and Coupland, 1966, Karamanski, 2000). In addition, G. paniculata is a prolific reproducer, with thousands of insect-pollinated flowers per individual (Darwent and Coupland, 1966). Replacement of native dune grassland by this forb drastically alters the diversity and physical structure of the plant community, and could have significant impacts on arthropods associated with these habitats.

In response to this invasion, The Nature Conservancy (TNC) and the U.S. National Park Service at Sleeping Bear Dunes National Lakeshore (SBDNL) initiated a multi-year effort in 2007 to remove G. paniculata from their properties in northwest Michigan (USA), in attempts to restore native sand dunes and their associated plant communities. The goal of this study is to evaluate the effects of this removal effort on arthropod communities. In particular, we ask (1) Do sites invaded by G. paniculata differ from reference sites in terms of arthropod abundance and diversity? (2) Does removal of G. paniculata correspond to shifts in arthropod communities towards that of the reference sites? (3) Do different functional groups of arthropods respond uniquely to invasion and removal of G. paniculata?