https://cpw.cvlcollections.org/files/original/75309dd5fc0acb2d45b344c98e783e15.pdf be854d9159f0f4f40c7e39c35def7bd4 PDF Text Text The research in this publication was partially or fully funded by Colorado Parks and Wildlife. Dan Prenzlow, Director, Colorado Parks and Wildlife • Parks and Wildlife Commission: Marvin McDaniel, Chair • Carrie Besnette Hauser, Vice-Chair Marie Haskett, Secretary • Taishya Adams • Betsy Blecha • Charles Garcia • Dallas May • Duke Phillips, IV • Luke B. Schafer • James Jay Tutchton • Eden Vardy �Contact networks reveal potential for interspecific interactions of sympatric wild felids driven by space use JESSE S. LEWIS,1,6, KENNETH A. LOGAN,2 MAT W. ALLDREDGE,3 DAVID M. THEOBALD,4 SUE VANDEWOUDE,5 AND KEVIN R. CROOKS1 1 Department of Fish, Wildlife, and Conservation Biology, Graduate Degree Program in Ecology, Colorado State University, Fort Collins, Colorado 80523 USA 2 Colorado Parks and Wildlife, Montrose, Colorado 81401 USA 3 Colorado Parks and Wildlife, Fort Collins, Colorado 80526 USA 4 Conservation Science Partners, Fort Collins, Colorado 80524 USA 5 Department of Microbiology, Immunology, and Pathology, Colorado State University, Fort Collins, Colorado 80523 USA Citation: Lewis, J. S., K. A. Logan, M. W. Alldredge, D. M. Theobald, S. VandeWoude, and K. R. Crooks. 2017. Contact networks reveal potential for interspecific interactions of sympatric wild felids driven by space use. Ecosphere 8(3): e01707. 10.1002/ecs2.1707 Abstract. Competitive interactions between species are fundamental to understanding species assemblages, community dynamics, and ecological processes. Anthropogenic landscape change, particularly resulting from urbanization, can alter interspecific interactions; however, different forms of urbanization are predicted to have contrasting effects on competitive interactions. We developed contact networks between bobcats and pumas to evaluate (1) the potential for interspecific interactions between wild felids and (2) how space-use metrics might change along the urban gradient, including low-density exurban development, wildland–urban interface, and wildland habitat, at both the population and individual level. We used an extensive telemetry data set for bobcats and pumas across multiple study areas to evaluate four space-use metrics: space-use overlap (used to define potential interactions among animals) and three additional contact network metrics, including degree (the number of potentially interacting animals), in-strength (sum of space-use overlap for animals), and equivalent social connectivity (ESC; considering both space-use extent and the amount of space-use overlap). Space-use extent was an important predictor of potential social interactions as measured by space-use metrics. Bobcats appeared to have a greater opportunity to interact with female pumas based on space-use overlap, degree, and in-strength, which demonstrates that relative scale of space-use extent among animals could be important for understanding interactions; ESC, however, was greater between bobcats and male pumas, likely due to the larger space-use extent by male compared to female pumas and the positive relationship between space-use extent and ESC. In addition, pumas and male bobcats exhibited a greater opportunity to interact, based on space-use overlap, degree, and in-strength, and demonstrated higher ESC compared to female bobcats. Counter to our predictions, felids associated with urbanized grids or with greater amounts of urbanization in their extent of space use did not appear to exhibit greater values of space-use metrics compared to animals with less exposure to urbanization; these results appear consistent with previous research evaluating population characteristics of felids across broad scales in our study areas. Greater ESC for male pumas and male bobcats suggests that males could be particularly important for facilitating connectivity of some ecological processes, such as the transmission of disease, through interspecific contact networks. Key words: bobcat; competition; development; exurban; Felis rufus; mountain lion; networks; Puma concolor; urbanization; wildland–urban interface. Received 10 January 2017; accepted 19 January 2017. Corresponding Editor: Robert R. Parmenter. Copyright: © 2017 Lewis et al. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. 6 Present address: Conservation Science Partners, Fort Collins, Colorado 80524 USA. E-mail: jslewis.research@gmail.com ❖ www.esajournals.org 1 March 2017 ❖ Volume 8(3) ❖ Article e01707 �LEWIS ET AL. INTRODUCTION extent and the strength of interactions among individuals. Although promising, these methods have not yet been applied to evaluate interspecific interactions of species in North America. Carnivore populations can be especially impacted by anthropogenic landscape change, which can alter population characteristics, spaceuse patterns, and interactions within and between species (Crooks 2002, Gehrt et al. 2010, Lewis et al. 2015b). Although prior research has focused on intraspecific (i.e., within species) interactions of carnivores in urban systems (Gehrt et al. 2010), relatively few studies have evaluated how urbanization influences interspecific (i.e., between species) interactions within the carnivore community. The intensity of competition and intra-guild predation among carnivore species is predicted to vary along the landscape gradient of urbanization (Crooks et al. 2010). At the urban extreme of the gradient, characterized by small, isolated habitat fragments immersed within a human-dominated matrix, the intensity of interspecific interactions is predicted to be relatively low due to the loss of larger, dominant predators and simplification of the ecological community (i.e., refugia hypothesis). Interaction strength is expected to be moderate at the natural end of the urban gradient, characterized by landscapes with relatively few to no human residences, where dominant and subordinate predators can coexist broadly and exhibit some degree of spatio-temporal avoidance within areas of sympatry. The most intense interspecific interactions are expected to occur at intermediate levels of urbanization, characterized by large areas of natural habitat adjacent to the urban interface, where dominant predators can still persist, but habitat and resource limitations heighten overlap in space use and thus antagonistic encounters with subordinant species (i.e., pile-up hypothesis). Within the Felidae family, pumas (Puma concolor) and bobcats (Lynx rufus) are solitary with similar social and spatial organization; typically, adult females have smaller home ranges that overlap little with neighboring females, whereas adult males have larger home ranges that typically overlap one to several females and sometimes neighboring males (Sandell 1989, Sunquist and Sunquist 2002, Logan and Sweanor 2010). Across broad scales, the distribution of bobcats Interactions among individuals are fundamental determinants of ecological communities, driving critical processes such as competition, predation, trophic cascades, disease spread, and ultimately the distribution and diversity of populations across fine to broad scales (MacArthur 1972, Rosenzweig 1995, Terborgh and Estes 2010). Landscape pattern, including that modified by anthropogenic activities, can shape animal distributions and competitive interactions and thus alters community-level processes (Forman 1995). In particular, urbanization can influence interactions of animals and lead to substantial impacts to ecological communities (Crooks and Soul�e 1999, Faeth et al. 2005). Urbanization, ranging from low-density exurban to high-density urban development (Theobald 2005), currently covers hundreds of million acres globally (Schneider et al. 2009, Nickerson et al. 2011) and is projected to expand by hundreds of millions of acres in the next few decades (Cohen 2003, Theobald 2005, Seto et al. 2011). Understanding how urbanization influences community interactions is essential to manage and conserve animal populations in developed landscapes (Magle et al. 2012), for example, as it relates to the spread of pathogens and zoonotic diseases increasing in prevalence in landscapes modified by humans (Daszak et al. 2000, Bradley and Altizer 2007). Social network analyses (i.e., contact networks, graph theory, network theory) provide a powerful tool to evaluate interactions among animals (Newman 2003, Craft and Caillaud 2011, Godfrey 2013), allowing comparisons of networks of animals in relation to anthropogenic factors (Wey et al. 2008). Various disciplines have created a variety of metrics within the network theory framework (e.g., social networks, landscape connectivity networks, technological networks) that might be applied to analyses of interactions among individuals. For example, unique metrics developed in the landscape connectivity literature that consider both spatial extent and strength of connectivity, such as probability of connectivity (PC; Saura and Pascual-Hortal 2007) and equivalent connectivity (EC; Saura et al. 2011), have potential to be effectively applied to social network analysis by considering both space-use ❖ www.esajournals.org 2 March 2017 ❖ Volume 8(3) ❖ Article e01707 �LEWIS ET AL. between the extent of space use for an animal and the number of potential interspecific interactions. Further, we expected that male pumas, given their larger home ranges (Logan and Sweanor 2001), would interact with a greater number of bobcats, but that female pumas would exhibit greater spatial overlap and in-strength with bobcats due to a more similar spatial scale in their extents of space use. Similarly for bobcats, we expected males to interact with a greater number of pumas, compared to females, and exhibit greater space-use overlap and in-strength due to more similar scales in their extents of space use. We also predicted that because males would use areas of greater spatial extent and interact with a greater number of felids, their ESC would be greater than that for females. At both the population and individual levels, we expected elevated opportunities for interspecific interactions (based on space-use metrics) in urbanized landscapes as predicted by the pile-up hypothesis (Crooks et al. 2010), specifically within exurban development and WUI habitat compared to wildland areas. and pumas overlaps extensively (Sunquist and Sunquist 2002) and both species overlap in their space use on finer scales in wildland habitat (Koehler and Hornocker 1991, Hass 2009, Lewis et al. 2015a). In addition, aggressive interactions occur between these felids and pumas will kill bobcats (Koehler and Hornocker 1991, Harveson et al. 2000). Both species are sensitive to anthropogenic disturbance but are also adaptable and able to persist in areas associated with urbanization (Crooks 2002, Beier et al. 2010, Riley et al. 2010). Bobcats and pumas typically occur at low population densities (Sandell 1989, Sunquist and Sunquist 2002); greater densities and overlap in space use between bobcats and pumas in areas influenced by urbanization could potentially lead to increased levels of competition, intra-guild predation, and cross-species disease transmission (Franklin et al. 2007, Crooks et al. 2010). For example, pumas acquired the bobcat strain of feline immunodeficiency virus (FIV) in urbanized California, presumably as a result of increased overlap of space use and contact rates near urban areas (Franklin et al. 2007). Although these felids appear to exhibit greater potential to interact at fine temporal scales in urbanized habitat (Lewis et al. 2015a), no empirical studies have explicitly evaluated how urbanization influences space-use overlap and interspecific interactions among known individuals of bobcats and pumas. We developed contact networks between bobcat and puma populations to understand how the potential for interspecific interactions varied across a gradient of urbanization. Using an extensive telemetry data set, we evaluated interspecific space-use patterns between bobcats and pumas across wildland, exurban development, and wildland–urban interface (WUI) habitat. Our analyses focused on four space-use metrics, including space-use overlap (used to define potential interactions among animals), degree (the number of potentially interacting animals), in-strength (sum of space-use overlap for animals), and equivalent social connectivity (ESC; considering space-use extent and overlap between animals). We tested specific predications regarding (1) potential interspecific interactions between bobcats and pumas and (2) how space-use metrics might change along the urban gradient at both the population and individual level. For each species, we predicted a positive relationship ❖ www.esajournals.org METHODS Study area We conducted our research across two study areas in Colorado, United States, that exhibited varying degrees of urbanization and human influence. In 2009–2010, we worked on the Western Slope (WS) of Colorado on the Uncompahgre Plateau near the towns of Montrose and Ridgway (Fig. 1). Common vegetation included pinyon pine (Pinus edulis), juniper (Juniperus osteosperma), ponderosa pine (Pinus ponderosa), aspen (Populus tremuloides), gambel oak (Quercus gambelii), and big sagebrush (Artemesia tridentata). We divided the WS study area into two sampling grids. The southern grid 1 sampled low-density residential development on Log Hill Mesa (population = 1041; U.S. Census Bureau 2010); residential parcel sizes were distributed, from most to least numerous, across 5 acre, 2 acre, 1 acre, ≥5 acre, and ≥40 acre properties. Within areas of exurban development, travel corridors of natural habitat and open space property, often with associated recreation trails, were present. The northern grid 2 sampled primarily undeveloped, wildland habitat, although some 3 March 2017 ❖ Volume 8(3) ❖ Article e01707 �LEWIS ET AL. Fig. 1. Locations of two study areas in Colorado, United States, which exhibited varying levels of urbanization, where bobcats and pumas were fit with telemetry collars. The more rural Western Slope (WS) was characterized by an exurban development south grid and a wildland north grid during 2009–2010. The more urbanized Front Range (FR) study area was characterized by a wildland–urban interface (WUI) south grid and wildland north grid during 2010–2012. Animal capture and telemetry data small areas of low-density human residences and hunting camps occurred on or near the grid. In 2010–2012, we worked on the more urbanized Front Range (FR) of Colorado (Fig. 1). Common vegetation included ponderosa pine, Douglasfir (Pseudotsuga menziesii), juniper, aspen, and mountain mahogany (Cercocarpus montanus). A network of open space properties with recreational trails occurred across the study area. Similar to the WS, we divided the FR study area into two sampling grids. The southern grid 1 occurred adjacent to the wildland–urban interface associated with the City of Boulder (population = 97,385, U.S. Census Bureau 2010) and was characterized by open space properties with some human residences on or near the grid. The northern grid 2 occurred across undeveloped public properties, although a small number of rural human residences occurred on private property inholdings. See Lewis et al. (2015b) for an expanded description of the study area. ❖ www.esajournals.org Bobcats were captured in black metal-wire cage traps (40 9 55 9 100 cm) with attractants from mid-June through March 2009–2011. All cage traps were fit with very high frequency (VHF) trap transmitters (Telonics, Mesa, Arizona, USA) that indicated when trap doors closed. Captured bobcats were immobilized through hand injection of a combination of ketamine (10.0 mg/kg) and xylazine (1.0 mg/km), and yohimbine (0.125 mg/km) was used to reverse xylazine (Kreeger et al. 2002). We fit GPS collars (210–280 g; Telemetry Solutions, Concord, California, USA) with timed drop-off mechanisms and degradable cotton spacers along the collar belting on adult-sized bobcats. GPS collars were programmed to record locations on the WS every 5–7 h and on the FR every 3–4 h. GPS collars were also equipped with VHF beacons that lasted up to 2 yr, which allowed for the continued monitoring of animals to assess site fidelity 4 March 2017 ❖ Volume 8(3) ❖ Article e01707 �LEWIS ET AL. for animals in which data were unavailable for an entire year, estimates of space use were assumed to be representative for annual periods; although GPS locations might be unavailable for some animals over annual periods (due to GPS battery expiration), VHF tracking of those animals enabled continued monitoring to assess whether individuals maintained site fidelity to an area. Each individual was assigned to the grid with the greatest proportion of its telemetry locations (for further description about time spent on grid techniques, see Lewis et al. 2015b). One male bobcat (i.e., M5) on the FR left the study area immediately after being captured and fit with a GPS collar, and thus, this individual was excluded from analyses. Space-use patterns of individuals were calculated by estimating the utilization distribution (UD) using telemetry locations of animals. For animals fit with GPS collars (bobcats n = 37; pumas n = 25), UDs were estimated with the Brownian bridge movement model (BBMM; Horne et al. 2007) at 30-m resolution with the mkde package (Tracey 2014) in program R (R Development Core Team 2014). The BBMM is appropriate to use with fine-scale GPS data sets because it is designed to be used with temporally correlated telemetry locations, incorporates information about animal movement into estimates of space use, and accounts for location error in estimates of UDs (Horne et al. 2007, Walter et al. 2011). For pumas on the WS fit with VHF collars (n = 4), UDs were estimated with the fixed kernel density home range estimator because data were not temporally correlated (i.e., independent locations obtained approximately two weeks apart); we used likelihood cross-validation to estimate the smoothing parameter (Horne and Garton 2006) in the Animal Space Use package (Horne and Garton 2009). We used the 99% cumulative probability of space use for all analyses. Both direct (the number of physical contacts between animals) and indirect (amount of shared space use) measures of animal interactions are important for understanding patterns of competition, predation, and disease transmission. Identifying direct interactions can be achieved through proximity collars or evaluating concurrent location data (Hamede et al. 2009, Schauber et al. 2015); however, challenges arise when spatial sampling techniques vary between animals, to an area. Bobcats were weighed, sex was recorded, and age was estimated based on tooth development (Crowe 1975), wear, and coloration. Pumas were captured from 2005 to 2011 with the use of hounds and baited cage traps, immobilized with Telazol (5.0–9.0 mg/kg) or a combination of medatomadine and ketamine, and fit with GPS collars (Lotek, Newmarket, Ontario, Canada; Northstar, King George, Virginia, USA; Vectronics, Berlin, Germany) programmed to record a location every 5–7 h on the WS and 3–4 h on the FR. To increase the duration of time that location data were acquired for pumas on the WS, four individuals were fit with VHF collars (Lotek) and aerial positional locations were obtained approximately every 2 weeks. Pumas were also weighed, fit with eartags, and age and sex were recorded. Methods for animal capture were approved by the Colorado State University Animal Care and Use Committee (11-2453A). Contact networks and metrics To evaluate the potential for interspecific interactions, we estimated space use for each individual fit with a telemetry collar and then calculated four metrics using these data. First, we estimated space-use overlap among all individuals and used this information to calculate three additional contact network metrics: degree, in-strength, and ESC. We refer to these measures collectively as spaceuse metrics. Telemetry data were used to estimate space use for felids that occurred on our sampling grids from June 2009 to June 2010 on the WS and September 2010 to September 2011 on the FR. Motion-activated cameras also operated during these periods of time (for additional details, see Lewis et al. 2015b) and assisted in evaluating which animals occurred on our sampling grids and assessing site fidelity of animals during our study. For animals known to occur on our grids during the focal periods, telemetry data before and after focal periods were used, if necessary, to estimate space use for an entire year (e.g., if telemetry data collection began in November 2010 for an animal, then space use would be estimated through October 2011). Because felids exhibit spatial fidelity (Sunquist and Sunquist 2002), we assumed that space use immediately before or after our focal period was similar and thus representative to that during focal periods. In addition, ❖ www.esajournals.org 5 March 2017 ❖ Volume 8(3) ❖ Article e01707 �LEWIS ET AL. in program R (R Development Core Team 2014). We used contact network metrics that evaluated patterns of space-use overlap among animals. Degree measures the number of edges connected to an individual (Newman 2003), which reflects the number of animals with which an individual potentially interacts (Wey et al. 2008). In-strength was calculated by summing space-use overlap (as estimated by UDOI). Edge weight (i.e., relationship strength) was calculated by estimating the space-use overlap (using the UDOI statistic) between each pair of animals, which evaluates the potential for repeated interactions between individuals (Wey et al. 2008). In-strength was then calculated by summing all the edge weights associated with a focal individual, and can effectively measure interaction strength among animals (Godfrey et al. 2010). The EC metric, originating from landscape ecology, evaluates how habitat patch size and connectedness affect landscape connectivity (Saura et al. 2011). Larger habitat patches are more effective than smaller patches in maintaining biodiversity, and more connected habitat patches facilitate the flow of ecological processes, including animal movement, through the landscape (Forman 1995, Rosenzweig 1995, Crooks and Sanjayan 2006). Thus, with the EC metric, larger habitat patches that are well connected to other patches result in greater landscape connectivity. Here, we apply the EC metric analogously to contact networks where individuals with greater space-use extents encounter more of the landscape and likely interact with more individuals, and increased overlap in space use between animals can increase potential interactions. Thus, within a contact network framework, we interpreted the EC metric as: vffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi uX n u n X EC ¼ t (2) ai aj p�ij when location data sets for study animals exhibit missing locations or do not completely overlap temporally, and when determining a subjective distance to define a contact. Although a coarser resolution, indirect methods can be used to address some of these challenges. Direct and indirect measures of animal interactions can be positively correlated (Vander Wal et al. 2014, Schauber et al. 2015), including for solitary carnivores (Robert et al. 2012), and space-use overlap is often used to evaluate the potential for animals to interact. To evaluate the opportunity for individuals to interact, we estimated space-use overlap among animals (Godfrey et al. 2010, Robert et al. 2012, Vander Wal et al. 2014, Melville et al. 2015, Schauber et al. 2015, Bauder et al. 2016) using the utilization distribution overlap index (UDOI) because this metric is most appropriate for evaluating the sharing of space use (Fieberg and Kochanny 2005). Utilization distribution overlap index measures the joint distribution of two UDs that overlap in space use: Z Z 11 d i ðx; yÞ � UD d j ðx; yÞdxdy UDOI ¼ Ai;j UD �1�1 (1) where Ai,j is the area of overlap between two anid i and UD d j are the estimated mal’s UDs and UD UDs for animals i and j, respectively (Fieberg and Kochanny 2005). Values of UDOI can range from 0 (no overlap) to >1 (if nonuniform UDs exhibit a high degree of overlap). Specifically, UDOI has a strong positive correlation with contact rates for solitary carnivores (Robert et al. 2012). Space-use overlap for an individual was calculated by averaging space-use overlap with all individuals with overlapping UDs. Contact networks represent individual animals as nodes and connections between individuals as edges to evaluate social interactions (Newman 2003). Covariates can be applied to nodes and edges, such as the size of the node (i.e., extent of individual space use) and edge weight (i.e., strength of two animals interacting). We defined potential interspecific interactions between two animals if their UDs overlapped (Godfrey et al. 2010, Vander Wal et al. 2014). To create figures of contact networks and visualize animal interactions, we used the igraph package (Csardi 2014) ❖ www.esajournals.org i¼1 j¼1 where ai and aj are the spatial extents of space use for animals i and j, and p�ij is the probability of two animals interacting. We defined p�ij as the overlap in space use between animals i and j using the Bhattacharyya’s affinity (BA) statistic (Fieberg and Kochanny 2005), which ranges between 0 and 1. Because we were interested in evaluating EC for individual animals, we simplified the EC metric to 6 March 2017 ❖ Volume 8(3) ❖ Article e01707 �LEWIS ET AL. including sex (male or female for focal individual), grid, space-use extent, and human development. The covariate grid compared interactions for animals associated with either exurban development and wildland areas (on the WS) or wildland– urban interface and wildland areas (on the FR). The covariate human development characterized the amount of human influence (Lewis et al. 2011) associated with each animal’s extent of space use. We created a human development layer where each human occurrence point (HOP; residence or structure) across study areas was digitized as a point using ArcGIS v10 software (ESRI, Redlands, California, USA) from color orthophotos (1-m resolution; Lewis et al. 2015b). Using Arc Toolbox in ArcMap10 (ESRI, Redlands, California, USA), we fit a Gaussian kernel with a radius of 1000 m over each HOP, where the density, or influence, was greatest directly at the point of interest and decreased out to the specified radius of a circle. A radius of 1000 m was used to predict the potential extent of disturbance from humans and urbanization on animals, as previous research reported animals responding to human disturbance at this distance (e.g., Siikam€aki and Kangas 2009, Donovan et al. 2011, Hamer and Parris 2011). The extent of space use for each individual was intersected with the GIS layer of human development, and we summed the total amount of human development within each animal’s extent of space use. Each continuous covariate was standardized by subtracting the sample mean from the input variable values and dividing by the standard deviation (Schielzeth 2010). For each response variable, we evaluated model sets comprising all possible combinations of covariates for each species in each study area and ranked models using Akaike’s Information Criteria corrected for small sample size (AICc; Burnham and Anderson 2002). To evaluate the importance of variables in models, we calculated variable importance values (VIV) and model-averaged parameter estimates across models in which they occurred (Burnham and Anderson 2002). calculate, what we refer to as, ESC for an individual animal (ESCi) as follows: vffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi uX u n ESCi ¼ t (3) ai aj p�ij j¼1 where ai is the space-use extent for the focal animal i and aj are the spatial extent of space use for animals j and p�ij is the BA value of space-use overlap between animals i and j. We defined ESC as the relative potential for an individual to contribute to the flow of ecological processes (i.e., connectivity) that are influenced by both node size (space-use extent) and edge weights (spaceuse overlap). Because ESC explicitly incorporates information about space-use extent, we expected these two metrics to be positively related. We defined social interactions as direct or indirect contacts occurring between animals, including both intra- (e.g., Seidensticker et al. 1973, VanderWaal et al. 2014) and interspecific interactions (Morse 1974). Statistical analyses Group-level evaluation: sex and urbanization.— For all metrics, we first calculated values for each individual animal and then averaged across individuals to estimate means and standard errors; comparisons of interactions between groups of animals were made, and we used two-sample t-tests to test for differences in contact metric values between males and females and animals using different levels of urbanization (exurban development and wildland habitat on the WS and wildland–urban interface and wildland habitat on FR) within each study area. Individual-level evaluation.—To evaluate how individuals responded to urbanization within their extents of space use, we used linear regression to evaluate the relationship between the space-use extent of animals and the number of potential interspecific interactions (i.e., degree) with neighboring individuals. We used multiple linear regression to evaluate how urbanization within an individual animal’s extent of space use influenced their potential interspecific contacts. Response variables as defined by space-use metrics (i.e., space-use overlap, degree, in-strength, and ESC) were evaluated in relation to a suite of predictor variables, ❖ www.esajournals.org RESULTS We used telemetry data from 19 bobcats and 10 pumas on the WS and 18 bobcats and 19 pumas on the FR to estimate space use, create contact networks (Fig. 2), and evaluate contact 7 March 2017 ❖ Volume 8(3) ❖ Article e01707 �LEWIS ET AL. Fig. 2. Contact networks of potential interspecific interactions between bobcats and pumas on the Western Slope (a) and Front Range (b), Colorado, demonstrating space-use overlap (overlap of utilization distributions among animals), degree (the number of connections to other animals), and in-strength (the sum of spatial overlap with all individuals). Dark orange circles represent pumas, and light blue circles represent bobcats. Circle (i.e., node) size is proportional to space-use extent on the log scale (values were multiplied by 3.5 to enhance visualization) for an individual, who is classified as either male (M) or female (F). The thickness of edges (i.e., edge weights) between individuals increases with the amount of space-use overlap (edge weights were multiplied by 15 to enhance visualization). Nodes were arranged from smallest to largest extents of space use across individuals for each species. across both the WS and FR (Fig. 3a, b; Appendix S1). However, bobcats had greater ESC with male compared to female pumas. Pumas exhibited greater potential to interact with male bobcats compared to female bobcats (Fig. 3c, d; Appendix S1). In general, pumas demonstrated greater space-use overlap with male bobcats, exhibited space-use overlap with a greater number of male bobcats (i.e., degree), and exhibited greater in-strength with male bobcats, compared to female bobcats, across both the WS and FR. In addition, pumas exhibited greater ESC with male compared to female bobcats. Group-level evaluation: urbanization Counter to our predictions, space-use metrics for bobcats and pumas did not appear to be greater in urbanized habitat compared to wildland areas. In both the WS and FR, felids demonstrated similar patterns of space-use overlap, spatially overlapped with similar numbers of individuals (i.e., degree), exhibited similar instrength, and had similar ESC values in urbanized (WS exurban; FR WUI) vs. wildland grids (Fig. 4; Appendix S2). network metrics. Figure 2 provides a visual summary of contact network metrics, including spaceuse overlap, degree, and in-strength in relation to space-use extent for bobcats and pumas on the WS and FR. Group-level evaluation: sex Bobcats exhibited greater potential to interact with female pumas compared to male pumas; as predicted, bobcats demonstrated greater spaceuse overlap with female pumas, spatially overlapped with a greater number of female pumas (i.e., degree), and exhibited greater in-strength with female pumas, compared to male pumas, ❖ www.esajournals.org Individual-level evaluation Potential interspecific interactions for individual animals were best explained by space-use extent, where individuals with larger extents of space use typically exhibited greater space-use 8 March 2017 ❖ Volume 8(3) ❖ Article e01707 �LEWIS ET AL. Fig. 3. Contact network statistics evaluating potential interactions between bobcats and pumas considering sex (i.e., male = M; female = F) on the Western Slope (WS) and Front Range (FR) of Colorado, including WS bobcats with male and female pumas (a), FR bobcats with male and female pumas (b), WS pumas with male and female bobcats (c), and FR pumas with male and female bobcats (d). Space-use overlap is the overlap of utilization distributions among animals, degree is the number of connections to other animals, in-strength is the sum of spatial overlap with all individuals, and equivalent social connectivity considers space-use extent and amount of space-use overlap among individuals. See Methods for further description of metrics. Boxes report the mean with one standard error, and whiskers demonstrate ranges (i.e., minimum and maximum values). An asterisk next to the metric indicates that differences were significant at a P-value of 0.05; see Appendix S1 for a summary of metric values and results of test statistics. overlap, degree, in-strength, and ESC; in general, space-use extent exhibited high VIV across models with parameter estimates that did not overlap 0 (Table 1; Appendix S3). However, space-use extent of pumas did not demonstrate a positive relationship with space-use overlap and in-strength with bobcats (Table 1), likely because pumas ❖ www.esajournals.org with smaller extents of space use (i.e., females) tended to exhibit greater use of shared areas with bobcats (Fig. 3a; Appendix S1). As predicted, there was a positive relationship between the extent of space use for bobcats and pumas and the number of potential interspecific contacts (i.e., degree) on the WS and FR (Fig. 5). 9 March 2017 ❖ Volume 8(3) ❖ Article e01707 �LEWIS ET AL. Fig. 4. Contact network statistics evaluating potential interactions between bobcats and pumas across different levels of urbanization on the Western Slope (WS; exurban vs. wildland) and Front Range (FR; wildland–urban interface (WUI) vs wildland) of Colorado, including WS bobcats with pumas (a), WS pumas with bobcats (b), FR bobcats with pumas (c), and FR pumas with bobcats (d). Space-use overlap is the overlap of utilization distributions among animals, degree is the number of connections to other animals, in-strength is the sum of spatial overlap with all individuals, and equivalent social connectivity considers space-use extent and amount of space-use overlap among individuals. See Methods for further description of metrics. Boxes report the mean with one standard error, and whiskers demonstrate ranges (i.e., minimum and maximum values). No differences were significant at a P-value of 0.05; see Appendix S2 for a summary of metric values and results of test statistics. Counter to predictions, we found little support in our models that space-use metrics were affected by the anthropogenic variables grid and human development, based on low VIV and model rankings, and 95% confidence intervals for parameter estimates overlapping 0 (Table 1; Appendix S3). Equivalent social connectivity of pumas on the WS was ❖ www.esajournals.org positively influenced by human development, with a high VIV and 95% confidence interval that did not overlap 0, possibly due to animals with larger extents of space use encountering a greater number of human residences. However, human development within an animal’s extent of space use appeared to be a poor predictor in all other analyses. 10 March 2017 ❖ Volume 8(3) ❖ Article e01707 �LEWIS ET AL. Table 1. Summary of results for covariates from multiple linear regression models evaluating potential felid interactions in relation to urbanization and space use for bobcats and pumas on the WS and FR of Colorado. Covariates Study area WS WS WS WS WS WS WS WS FR FR FR FR FR FR FR FR Grid Space-use extent Human development Comparison Response variable VIV b (SE) VIV b (SE) VIV b (SE) Bobcats with pumas Bobcats with pumas Bobcats with pumas Bobcats with pumas Pumas with bobcats Pumas with bobcats Pumas with bobcats Pumas with bobcats Bobcats with pumas Bobcats with pumas Bobcats with pumas Bobcats with pumas Pumas with bobcats Pumas with bobcats Pumas with bobcats Pumas with bobcats Space-use overlap Degree In-strength ESC Space-use overlap Degree In-strength ESC Space-use overlap Degree In-strength ESC Space-use overlap Degree In-strength ESC 0.20 0.27 0.17 0.99 0.38 0.11 0.27 0.04 0.17 0.24 0.16 0.34 0.17 0.33 0.30 0.19 0.01 (0.02) �0.39 (0.39) 0.04 (0.09) 17.76 (4.13) �0.07 (0.04) 3.07 (4.10) �0.63 (0.41) 13.18 (30.83) 0.00 (0.03) �1.04 (1.06) �0.02 (0.37) 29.91 (22.03) 0.00 (0.03) 2.39 (1.92) 0.38 (0.35) 10.49 (18.01) 0.95 0.90 1.00 1.00 0.26 0.41 0.20 1.00 0.45 0.97 0.65 1.00 0.70 0.82 0.37 1.00 0.02 (0.01) 0.45 (0.16) 0.19 (0.04) 46.51 (2.07) �0.03 (0.02) 3.12 (1.59) �0.27 (0.20) 59.36 (11.30) 0.02 (0.01) 1.77 (0.53) 0.36 (0.17) 48.25 (11.33) �0.03 (0.01) 2.25 (0.86) �0.23 (0.17) 65.80 (8.75) 0.25 0.24 0.19 0.15 0.10 0.15 0.09 0.80 0.19 0.15 0.21 0.15 0.25 0.26 0.20 0.17 0.01 (0.01) �0.18 (0.22) 0.03 (0.05) �1.34 (3.04) �0.01 (0.03) 2.12 (1.94) 0.04 (0.24) 30.44 (9.80) 0.01 (0.01) 0.05 (0.58) 0.14 (0.19) 1.63 (12.49) �0.01 (0.02) 1.09 (1.19) �0.06 (0.20) 3.38 (10.32) Notes: Covariates included grid (sampling grid areas comparing urbanized [=0] and wildland grids [=1]), space-use extent (extent of space use for animals), and human development (influence of human development at a kernel density radius of 1000 m). VIV were calculated across model sets comprising all possible combinations of covariates. Parameter estimates (b) and standard errors (SE) were calculated by model averaging across all models in a model set in which the variable occurred. ESC, equivalent social connectivity; FR, Front Range; VIV, variable importance values; WS, Western Slope. DISCUSSION Greater opportunities for interspecific interactions between male pumas and male bobcats based on both space-use extent and overlap (i.e., ESC) suggest that males could be especially important for facilitating connectivity of particular ecological processes, such as the transmission of disease, through contact networks. Consistent with many species of felids, males and females within both bobcats and pumas demonstrate varying space-use and behavioral patterns (Sunquist and Sunquist 2002, Macdonald and Loveridge 2010, Loveridge et al. 2016). Thus, although space-use extent clearly influenced contact networks between bobcats and pumas in our study, and patterns of space use is related to gender, other behavioral differences between males and females likely influence interspecific interactions. For example, male and female felids exhibit different life history strategies and expressions of aggression (Logan and Sweanor 2001, 2010, Sunquist and Sunquist 2002). Typically, adult males tend to be more aggressive than females, who may be more cautious to protect young and avoid infanticide. The aggressive behavior of males can lead to intraspecific killing within The potential for interspecific interactions between bobcats and pumas varied by extent of space use and sex (based on group-level analyses) but, counter to our predictions, space-use metrics were similar between urbanized and wildland grids (based on individual-level analyses). Across study areas, bobcats tended to exhibit a greater opportunity to interact with female pumas, based on values of three space-use metrics (i.e., space-use overlap, degree, and in-strength). This result highlights that relative scale of space use might be an important driver of interspecific interactions, with female pumas exhibiting smaller space-use extents that were more comparable to those of bobcats. The metric ESC, however, was greater between bobcats and male pumas, likely due to the larger extents of space use of male compared to female pumas and the positive relationship between space-use extent and ESC. Our results of space-use metrics also suggest that pumas were more likely to interact with male bobcats, again likely because male bobcats exhibited greater space-use extents that were more similar in scale to those of pumas. ❖ www.esajournals.org 11 March 2017 ❖ Volume 8(3) ❖ Article e01707 �LEWIS ET AL. Fig. 5. The number of potential interspecific interactions (i.e., degree) increased with the extent of space use for bobcats (a) and pumas (b) on the Western Slope and bobcats (c) and pumas (d) on the Front Range of Colorado. Degree is the number of individuals that overlapped in space use and thus had the potential to interact. influenced by sex, body size, social status, community interactions, and food availability both spatially and temporally (Knick 1990, Sunquist and Sunquist 2002, Ferguson et al. 2009, Fattebert et al. 2016). In addition, transient and resident animals can exhibit different types of behaviors (e.g., mating or fighting to maintain or obtain a home range), which could be important in understanding the types of social encounters experienced during interactions. Typically, transient, dispersing animals may travel farther distances, potentially increasing the probability of contact with other animals and consequently conflict or disease transmission (Tracey et al. 2014). Anthropogenic factors can also be important determinants of animal space use, which can influence interspecific interactions. In particular, urbanization can influence both space-use extent and animal interactions (Gehrt et al. 2010), with the potential for contrasting effects (Riley et al. puma populations (Logan and Sweanor 2001, 2010), and if such aggression also translates across species, then male pumas might be likely to exhibit interspecific killing and aggressive interactions toward bobcats as well. However, female pumas also might exhibit aggression toward bobcats if increased space-use overlap and use of small to mid-sized prey (Murphy and Ruth 2010) intensifies competition with bobcats. Ultimately, varying behavioral strategies between sexes could influence patterns of space use and habitat selection between males and females and ultimately influence interspecific interactions and opportunities for interspecific killing and intra-guild predation. For each species, values of the four space-use metrics generally increased with the extent of space use for individuals. Thus, ecological factors leading to greater space-use extents for animals would be predicted to increase the opportunity for interactions. For example, space use can be ❖ www.esajournals.org 12 March 2017 ❖ Volume 8(3) ❖ Article e01707 �LEWIS ET AL. interaction opportunities were not greater in urbanized areas (Lewis et al. 2015a). Further, population densities of bobcats and pumas were either lower or similar in urbanized habitat compared to wildland areas (Lewis et al. 2015b), suggesting that urbanization did not intensify interspecific interactions via density inflation at broad scales. Fine-scale analyses, however, concluded that interaction opportunities between pumas and bobcats were greater in urbanized areas, but only at fine temporal and spatial scales (i.e., across daily time periods; Lewis et al. 2015a). Importantly, the space-use metrics used in our contact networks do not measure the number of direct interactions between animals, but rather the potential for animals to interact. Although direct and indirect methods to estimate interactions can be positively correlated (Robert et al. 2012, Vander Wal et al. 2014, Schauber et al. 2015), the relationship between space use and contact rates can also be variable (Schauber et al. 2007). Consequently, future analyses evaluating direct interactions among animals could provide more insight on interspecific interactions at finer scales. For example, direct interactions could be analyzed using high-resolution concurrent GPS data or proximity collars (e.g., Hamede et al. 2009, Schauber et al. 2015). It would be predicted that finer-scale direct contacts between species might vary depending on animal behavior and landscape characteristics influenced by urbanization (e.g., Crooks et al. 2010). In addition, bobcats and pumas exhibit broad areas of space use and urban-associated felids can spend considerable time away from urbanized areas, such as when undeveloped habitat is adjacent to urbanization. Thus, fine-scale analyses could compare direct interspecific interactions between individual felids relative to the proximity to urbanization. Although contact networks provide a powerful tool to investigate potential interactions among animals, there are limitations to this approach. For example, in telemetry studies, it is very challenging, if not impossible, to fit all animals with tracking collars, and thus, contact network metrics reflect the sampled population and likely an incomplete analysis of interactions among all individuals in a population. In addition, contact network metrics are dependent upon the spatial distribution of collared animals relative to the 2010). Space-use extent can be positively correlated with urbanization where greater amounts of urbanization within an individual’s home range are related to larger extents of space use (Riley et al. 2003). Ultimately, our study suggests that greater space-use extent may increase the probability of interspecific interactions between felids. Conversely, urbanization can decrease home range size if development reduces landscape permeability and restricts movement. In this case, restricted space-use extent in urban areas may decrease the likelihood of interspecific interactions between bobcats and pumas. However, if smaller home ranges are accompanied by increased space-use overlap and inflated local densities along impermeable boundaries, then this might intensify probability of interactions, as predicted by the pile-up hypothesis (Riley et al. 2006, Crooks et al. 2010). Although few studies have evaluated the impacts of disturbance from human activities on space use and animal interactions, our results support the conceptual effects of how urbanization could alter community ecology of carnivores (Crooks et al. 2010). Despite these potential mechanisms, space-use metrics for bobcats and pumas did not significantly differ among varying levels of urbanization at either individual or population levels. Increased interactions might be more likely to occur in landscapes with greater extents of urbanization or those that are more fragmented than our study, such as in habitat patches completely surrounded by urbanization (e.g., fence effect; Krebs et al. 1969, Adler and Levins 1994). For example, greater overlap in space use among animals was observed for populations persisting in highly fragmented habitat patches (Riley et al. 2006) and areas associated with higher levels of urbanization than characterized by our study. Further, increased space-use overlap might occur for specific age and sex classes within populations (e.g., adult females; Riley et al. 2006), but our sample sizes did not allow for such evaluations and this would be an important area of future study. When animals use habitat directly influenced by urbanization, the opportunity for interactions can vary depending upon spatial and temporal scales. Our results are consistent with previous research in this system at broad scales, which demonstrated that pumas did not exclude bobcats from urbanized or wildland areas and ❖ www.esajournals.org 13 March 2017 ❖ Volume 8(3) ❖ Article e01707 �LEWIS ET AL. sampled population, which can result in boundary effects (Craft et al. 2009). Although metrics evaluating the importance of nodes within a network, such as centrality, closeness centrality, and betweenness centrality, can provide valuable information about network structure (Newman 2003), such metrics can be sensitive to small sample size and node position within the network (Wey et al. 2008) and were not considered in our analysis. However, contact network metrics can be robust to small sample sizes (Wey et al. 2008), and we used metrics and analyses that aimed to minimize such limitations and focused on metrics that evaluated the potential for animals to interact based on space-use patterns. The application of contact network analyses to wildlife management and conservation has received increasing attention (Wey et al. 2008). Although much research has focused on using contact networks to evaluate questions investigating disease transmission in animals (Craft and Caillaud 2011, Godfrey 2013), this framework can also be used to ask more general ecological questions about social relationships within and between species (Wey et al. 2008). In particular, contact networks provide researchers with a suite of metrics across disciplines that can be related to ecological and demographic characteristics in a model selection framework to test competing hypotheses. For example, we demonstrated how contact network metrics originating from landscape ecology (e.g., the ESC metric) can be used to evaluate the relative importance of space-use and landscape characteristics in explaining potential competitive interactions. Such information can be used to understand how potential animal interactions are influenced by sex and levels of urbanization. This framework using contact networks can be applied widely to diverse systems to better understand space-use patterns in relation to social, landscape, and ecological factors. greatly thank Robert Alonso, Brady Dunne, Michelle Durant, Dana Morin, and Linda Sweanor for their invaluable work in the field, Jeff Tracey for assistance with estimating space use in R, and John Fieberg for guidance in evaluating space-use overlap. In addition, we thank the numerous landowners who allowed us access to their properties for our research. We appreciate the helpful comments from Larissa Bailey and anonymous reviewers, which greatly improved the manuscript. LITERATURE CITED Adler, G. H., and R. Levins. 1994. The island syndrome in rodent populations. Quarterly Review of Biology 69:473–490. Bauder, J. M., D. R. Breininger, M. R. Bolt, M. L. Legare, C. L. Jenkins, B. B. Rothermel, and K. McGarigal. 2016. 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Census demographic profiles interactive population map. https://www.census. gov/2010census/popmap/ SUPPORTING INFORMATION Additional Supporting Information may be found online at: http://onlinelibrary.wiley.com/doi/10.1002/ecs2. 1707/full ❖ www.esajournals.org 17 March 2017 ❖ Volume 8(3) ❖ Article e01707 � https://cpw.cvlcollections.org/files/original/b22f642dca7a01f4b7981759fd310dcd.zip 6ba526593bf926ca7f20588db6316d58 Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Journal Articles Description An account of the resource CPW peer-reviewed journal publications Text A resource consisting primarily of words for reading. Examples include books, letters, dissertations, poems, newspapers, articles, archives of mailing lists. Note that facsimiles or images of texts are still of the genre Text. Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Contact networks reveal potential for interspecific interactions of sympatric wild felids driven by space use Description An account of the resource <span>Competitive interactions between species are fundamental to understanding species assemblages, community dynamics, and ecological processes. Anthropogenic landscape change, particularly resulting from urbanization, can alter interspecific interactions; however, different forms of urbanization are predicted to have contrasting effects on competitive interactions. We developed contact networks between bobcats and pumas to evaluate (1) the potential for interspecific interactions between wild felids and (2) how space-use metrics might change along the urban gradient, including low-density exurban development, wildland–urban interface, and wildland habitat, at both the population and individual level. We used an extensive telemetry data set for bobcats and pumas across multiple study areas to evaluate four space-use metrics: </span><i>space-use overlap</i><span> (used to define potential interactions among animals) and three additional contact network metrics, including </span><i>degree</i><span> (the number of potentially interacting animals), </span><i>in-strength</i><span> (sum of space-use overlap for animals), and equivalent social connectivity (ESC; considering both space-use extent and the amount of space-use overlap). Space-use extent was an important predictor of potential social interactions as measured by space-use metrics. Bobcats appeared to have a greater opportunity to interact with female pumas based on </span><i>space-use overlap</i><span>,</span><i><span> </span>degree</i><span>, and </span><i>in-strength</i><span>, which demonstrates that relative scale of space-use extent among animals could be important for understanding interactions; ESC, however, was greater between bobcats and male pumas, likely due to the larger space-use extent by male compared to female pumas and the positive relationship between space-use extent and ESC. In addition, pumas and male bobcats exhibited a greater opportunity to interact, based on </span><i>space-use overlap</i><span>,</span><i><span> </span>degree</i><span>, and </span><i>in-strength</i><span>, and demonstrated higher ESC compared to female bobcats. Counter to our predictions, felids associated with urbanized grids or with greater amounts of urbanization in their extent of space use did not appear to exhibit greater values of space-use metrics compared to animals with less exposure to urbanization; these results appear consistent with previous research evaluating population characteristics of felids across broad scales in our study areas. Greater ESC for male pumas and male bobcats suggests that males could be particularly important for facilitating connectivity of some ecological processes, such as the transmission of disease, through interspecific contact networks.</span> Bibliographic Citation A bibliographic reference for the resource. Recommended practice is to include sufficient bibliographic detail to identify the resource as unambiguously as possible. Lewis, J. S., K. A. Logan, M. W. Alldredge, D. M. Theobald, S. VandeWoude, and K. R. Crooks. 2017. Contact networks reveal potential for interspecific interactions of sympatric wild felids driven by space use. Ecosphere 8(3):e01707. <a href="https://doi.org/10.1002/ecs2.1707" target="_blank" rel="noreferrer noopener">https://doi.org/10.1002/ecs2.1707</a> Creator An entity primarily responsible for making the resource Lewis, Jesse S. Logan, Kenneth A. Alldredge, Mathew W. Theobald, David M. VandeWoude, Sue Crooks, Kevin R. Subject The topic of the resource Bobcat Competition Development Exurban <em>Felis rufus</em> Mountain lion Networks <em>Puma concolor</em> Urbanization Wildland–urban interface Extent The size or duration of the resource. 17 pages Date Created Date of creation of the resource. 2017-03-02 Rights Information about rights held in and over the resource <a href="http://rightsstatements.org/vocab/InC-NC/1.0/" target="_blank" rel="noreferrer noopener">In Copyright - Non-Commercial Use Permitted</a> <a href="https://creativecommons.org/licenses/by-nc/4.0/" target="_blank" rel="noreferrer noopener">Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)</a> Format The file format, physical medium, or dimensions of the resource application/pdf Language A language of the resource English Is Part Of A related resource in which the described resource is physically or logically included. Ecosphere Type The nature or genre of the resource Article