Urban Areas May Serve As Habitat and Corridors for Dry-Adapted, Heat Tolerant Species; an Example from Ants

Urban Ecosyst (2011) 14:135–163 DOI 10.1007/s11252-010-0150-7 Urban areas may serve as habitat and corridors for dry-adapted, heat tolerant species; an example from ants Sean B. Menke & Benoit Guénard & Joseph O. Sexton & Michael D. Weiser & Robert R. Dunn & Jules Silverman Published online: 9 September 2010 # Springer Science+Business Media, LLC 2010 Abstract We collected ants from six urban and one forest land-use types in Raleigh, NC to examine the effects of urbanization on species richness and assemblage composition. Since urban areas are warmer (i.e., heat island effect) we also tested if cities were inhabited by species from warmer/drier environments. Species richness was lower in industrial areas relative to other urban and natural environments. There are two distinct ant assemblages; 1) areas with thick canopy cover, and 2) more disturbed open urban areas. Native ant assemblages in open environments have more southwestern (i.e., warmer/drier) distributions than forest assemblages. High native species richness suggests that urban environments may allow species to persist that are disappearing from natural habitat fragments. The subset of species adapted to warmer/drier environments indicates that urban areas may facilitate the S. B. Menke (*) : J. Silverman Department of Entomology, North Carolina State University, 3324 Gardner Hall, Box 7613, Raleigh, NC 27695-7613, USA e-mail: [email protected] J. Silverman e-mail: [email protected] S. B. Menke : B. Guénard : M. D. Weiser : R. R. Dunn Department of Biology, North Carolina State University, Raleigh, NC, USA B. Guénard e-mail: [email protected] M. D. Weiser e-mail: [email protected] R. R. Dunn e-mail: [email protected] S. B. Menke : B. Guénard : R. R. Dunn W.M. Keck Center for Behavioral Biology, North Carolina State University, Raleigh, NC, USA J. O. Sexton Biospheric Sciences Branch, NASA Goddard Spaceflight Center, Greenbelt, MD, USA e-mail: [email protected] 136 Urban Ecosyst (2011) 14:135–163 movement of some species. This suggests that urban adapted ants may be particularly successful at tracking future climate change. Keywords Urban heat island . Range shift . Ant diversity . Urban ecology Introduction As global populations rise, many rural areas are experiencing human population declines due to migration to cities (Miller and Hobbs 2002; United Nations 2007). Most people now live in urban environments, the fastest growing environment globally (United Nations 2007). Therefore, the wildlife species most people encounter are species in urban environments (Dunn et al. 2006; Shochat et al. 2006). Species in urban environments can derive from the local “native” species pool, but also from non-native species (including invasive and pest species) from the global pool (Mack and Lonsdale 2001; McKinney 2006; Kark et al. 2007). To date, work aimed at understanding urban biomes has focused on the degradation or conservation of patches of “natural” environments and the organisms that persist in them (Bolger et al. 2000; McKinney 2006; Williams et al. 2009). Yet the less studied urban matrix of cement and lawns in which these “natural” patches reside represents one of the fastest growing biomes in the world (United Nations 2007). The origins of urban species and composition of urban faunas in both the “natural” and novel elements of urban landscapes is fundamental to understanding the biological world we most often experience. Given the recognized importance of arthropods both in terms of ecosystem services and disservices and as a model system for other organisms (e.g., McIntyre 2009), studies of urban arthropod communities have been surprisingly rare and often limited in scope. Ants in particular are important because they respond rapidly to environmental change, represent a variety of trophic levels, are important ecosystem engineers, and are of major economic concern (Hölldobler and Wilson 1990;Hedges1998;Holwayetal.2002; Underwood and Fisher 2006). Most studies on ants have focused on fragments of natural habitats in urban environments and the differences in species richness across urban to rural gradients, with often inconsistent patterns between cities (McKinney 2008; McIntyre 2009). For example, a number of studies of ants have shown decreases in species richness in urban environments (Pisarski and Czechowski 1978;Suarezetal.1998; Malozemova and Malozemov 1999; Yamaguchi 2004; Lessard and Buddle 2005; Pacheco and Vasconcelos 2007; Thompson and McLachlan 2007; Clarke et al. 2008) though others have shown little to no difference (Carpintero et al. 2003; Gibb and Hochuli 2003; Forys and Allen 2005; Vepsäläinen et al. 2008). Few a priori predictions for species richness and structure of urban assemblages exist. General statements in the literature argue that a subset of “generalist” species, especially in arthropods, do well in urban environments (e.g., more cement, fewer trees, smaller patches of native and exotic plants) (McIntyre 2009). In ants, it has been reported that such species tend to be non-native, or behaviorally dominant species which are able to defend resources and displace other ants at local scales (Pisarski and Czechowski 1978; Malozemova and Malozemov 1999; Carpintero et al. 2003; Gibb and Hochuli 2003; Yamaguchi 2004; Holway and Suarez 2006; Vepsäläinen et al. 2008; Stringer et al. 2009). But, there are few empirical studies that support the hypothesis that generalist species do better than other species in urban environments (McKinney 2008; Lach et al. 2010). An important next step is to consider the traits of such favored urban species in more detail. It remains conceivable that the species that do well with urbanization are generalists in some regards, but also tend to possess specific traits that predispose them to urban success. For example, Lundholm and Urban Ecosyst (2011) 14:135–163 137 Marlin (2006) have suggested that urban environments most closely approximate cliff or talus slope environments, and so species inhabiting cities often have origins in cliff-like habitats, even though such habitats are globally rare. Separately, in a review of this work, Gamble (2004) argued that some forest canopy species (e.g., some lichens and mosses on buildings) should succeed in some urban environments (Delgadillo and Cardenas 2000). A more inclusive version of the cliff-side hypothesis is that urban species should come from open or more exposed habitats, including but not exclusive to cliff-sides and forest canopies. Urban environments also differ from surrounding natural areas in their climate due to the urban heat island effect (Grimm et al. 2008). Urban environments are warmer, especially in the evening, than adjacent non-urban areas, and this difference in temperatures is often greater that the predicted global temperature change (Grimm et al. 2008). Therefore, another though not exclusive possibility is that the species in the most open urban environments come disproportionately from species in warmer and drier environments (Bernard 1958; Pisarski and Czechowski 1978). Here we address three broadly overlapping questions. While characterizing ant assemblages relative to different urban environments, we ask: 1) Does ant species richness decrease as a function of urbanization along a gradient of “natural” forest environments to intensive open urban areas?; 2) Do different urban environments support different ant assemblages?; and, 3) Does increasing urbanization favor a group of species found in warmer and drier natural environments (analogous to warmer/drier urban areas)? To address these questions we sampled ant assemblages from urban and natural areas in North Carolina, USA, and developed a database of the biogeographic and climatic traits of all ant species found along that gradient. Methods Study site and sampling The city of Raleigh is located in northeast central North Carolina at the intersection of the Piedmont and Atlantic Coastal Plain biomes. North Carolina is a transition area were northern and southern faunas intersect (Carter 1962). As of the 2006 census, Raleigh was home to about 356,000 people and covered 299 km2. We used the Wake_Zoning_2006 GIS data-layer to quantify different urban land-use habitats (http://www.wakegov.com). City zoning classifications were broken into six urban land-use types: (ordered by percent coverage) agriculture (4.2%), greenway (4.4%), industrial (10.6%), business (11.1%), park (11.3%), and residential (58.3%). Coordinates for 10 sites were randomly selected for each land-use type except for residential in which 30 sites were randomly selected (Fig. 1). In addition, we sampled 10 natural forested sites from the surrounding area outside the city boundaries. Forested sites were upland hardwood or pine—hardwood mature secondary forests. All sites were randomly selected using Hawth’s Tools for ArcGIS (Beyer 2004). Each site was sampled with five pitfall traps arranged in the shape of a 5 on a die separated by 20 m on a side. Pitfall traps consisted of 50 mL centrifuge tube filled with a water / alcohol / glycerol solution and left open for 5 days. All sampling occurred during 29 May– 17 June 2008. All ants were identified to species and voucher specimens are deposited at the Bohart Museum of Entomology, University of California Davis (UCDC). Each species was assigned one of four categories (forest specialist, open specialist, generalist, or invasive) based on literature and expert knowledge. 138 Urban Ecosyst (2011) 14:135–163 Fig. 1 Sample locations in Raleigh, North Carolina urban land-use

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