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Overwintering Anuran Niche Preferences in a Series of Interconnected Ponds in Northwestern Florida
Caleb M. Bomske and Nate Bickford

Southeastern Naturalist, Volume 18, Issue 2 (2019): 256–269

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Southeastern Naturalist C.M. Bomske and N. Bickford 2019 Vol. 18, No. 2 256 2019 SOUTHEASTERN NATURALIST 18(2):256–269 Overwintering Anuran Niche Preferences in a Series of Interconnected Ponds in Northwestern Florida Caleb M. Bomske1,* and Nate Bickford2,3 Abstract - This study identified variations in pond bank gradients and associated plant assemblages to better understand niche preferences of 3 species of overwintering anurans— Acris gryllus (Southern Cricket Frog), Lithobates grylio (Pig Frog), and Lithobates sphenocephalus (Southern Leopard Frog)—in northwest Florida (Escambia County). We selected 7 regions of 4 interconnected ponds in a coastal pine flatwoods wetland. We conducted visual and auditory surveys once every week for 10 weeks from 17 January to 24 March 2017. We categorized survey areas along pond shorelines by the plant assemblage composition and species richness, pond bank steepness, and sunlight exposure. We looked for correlations between each species and specific niche characteristics. None of the anuran species studied showed a preference for the amount of sunlight or the slope of the pond bank. However, plant species richness was positively correlated with Southern Cricket Frogs and negatively correlated with Pig Frogs; thus, there was a very strong negative correlation between Pig Frogs and Southern Cricket Frogs. Southern Cricket Frogs, the smallest frog species in this study, prefers high plant species richness, possibly for increased cover from predators, and avoids potential predators like Pig Frogs. Pig Frogs prefer lower species richness, relying on open water for escape. The Southern Leopard Frog showed no vegetation preferences, possibly because the species is more adaptable and has a variety of predator evasion methods. Wetland plant assemblages are an accurate reflection of life-history habits of anurans, particularly predator evasion tactics. Introduction Florida is a hotspot of reptile and amphibian diversity (Blaustein 2008, Farrell et al. 2011). As one of the 5 most biodiverse regions in North America, no other place in the US or Canada has more species of frogs than northwestern Florida (Blaustein 2008). However, amphibians, including anurans, are currently in sharp decline globally (Catenazzi et al. 2011, Gallant et al. 2007) and Florida is not an exception (Cassani et al. 2015). Temperate regions like the US, which already have lower anuran diversity than the tropics, are at a higher risk to environmental stressors (Wiens 2007). Anurans are sometimes considered environmental indicators of ecosystem health (Guzy et al. 2012, Kerby et al. 2010, Niemi et al. 2007, Welsh and Ollivier 1998). Therefore, identifying the environmental factors, such as plant diversity (Chandler et al. 2015, Cunningham et al. 2007, Sasaki et al. 2015, Shulse et al. 2012), that contribute to anuran biodiversity is crucial to understanding and preserving ecosystem health in the future. 1Department of Horticulture and Natural Resources, Kansas State University, Manhattan, KS 66506. 2Department of Biology, University of Nebraska, Kearney, NE 68849.3Current address - Departmet of Biology, Colorado State University Pueblo, Pueblo, CO 81001. *Corresponding author - Manuscript Editor: Scott Markwith Southeastern Naturalist 257 C.M. Bomske and N. Bickford 2019 Vol. 18, No. 2 Many studies have focused on wide-scale environmental factors that influence amphibian abundances. The availability of high-quality habitat is an accurate predictor of frog abundances (Ficetola et al. 2015). Habitat fragmentation and loss are among the leading causes of amphibian declines (Anderson et al. 2004, Becker et al. 2007, Cushman 2006, Delis et al. 1996, Gallant et al. 2007, Lehtinen et al. 1999). However, frog diversity is sometimes greater in agricultural farm ponds than in native woodland ponds (Alix et al. 2014) and some species, such as Lithobates sphenocephalus (Cope) (Southern Leopard Frog), actually prefer agricultural influences (Alix et al. 2014). Even when species richness increases in a landscape fragmented by agriculture, logging, and development, behavioral diversity, such as reproductive modes, usually declines (Almeida-Gomes and Rocha 2015, Bickford et al. 2010). Many anuran species are completely absent from urbanized areas (Guzy et al. 2012). Hylids (treefrogs), like Acris gryllus (LeConte) (Southern Cricket Frog), are particularly sensitive to habitat changes (Alix et al. 2014, Anderson et al. 2004, Delis et al. 1996, Fardell et al. 2018). Areas of greater amphibian species richness are currently experiencing the highest rates of habitat loss (Gallant et al. 2007). A deeper understanding of habitat use among amphibians is crucial to their preservation. Comparatively few studies have attempted to characterize frog habitat use on a fine scale, but microhabitat characteristics are crucial to anuran breeding success and resource partitioning (Baldwin et al. 2006, Gorman and Haas 2011). Many ranids (like Lithobates) utilize non-breeding habitats seasonally, so conservation of adjacent upland areas is important (Baldwin et al. 2006, Blihovde 2006, Fellers and Kleeman 2007, Grand et al. 2017, Harper et al. 2008, Pitt et al. 2017, Regosin et al. 2003). Unfortunately, most studies that investigated anuran microhabitat selection have focused on northern species that hibernate and, therefore, shed little light on the winter habitat preferences of subtropical (Florida) ranids like the Southern Leopard Frog and Lithobates grylio Stejneger (Pig Frog). Even studies that had more-comprehensive data collection times only recorded presence or absence for ranids at sites (Baskale and Çapar 2016), which says little of niche preferences within suitable habitat. Some studies have indicated that changes in vegetation have an insignificant effect on amphibian communities on a broad scale (Chandler et al. 2015) and that shallow littoral zones are much better predictors of amphibian species richness then vegetation (Porej and Hetherington 2005). However, amphibian diversity is usually associated with high plant species richness (Cunningham et al. 2007, Sasaki et al. 2015, Shulse et al. 2012) and increased canopy cover (Baskale and Çapar 2016, Werner et al. 2007). Water chemistry, which can be influenced by plant species, also has an influence on anuran habitat choices (Baskale and Çapar 2016). Compounds from the invasive Triadica sebifera (L.) Small (Chinese Tallow) are known to inhibit Southern Leopard Frog larval development if leaf litter is allowed to decompose in the water (Adams and Saenz 2012). Other wetland species can impact anuran abundances. The presence of predatory fish normally decreases the abundances of ranids like the Southern Leopard Frog and Pig Frog (Holbrook and Dorn 2016, Porej and Hetherington 2005). Invasive Southeastern Naturalist C.M. Bomske and N. Bickford 2019 Vol. 18, No. 2 258 Pomacea maculata Perry (Apple Snail) also depredate anuran eggs (Carter et al. 2018). Other predators, such as snakes and turtles, may also influence anuran species assemblages. Ecosystem engineers, like Castor canadensis Kuhl (North American Beaver, hereafter, Beaver), also have an effect on anuran diversity and abundance (Wright et al. 2002). More research is needed on the niche and microhabitat level to understand anuran habitat preferences. All 3 of the species in this study can be considered habitat generalists and 2, the Southern Cricket Frog and Southern Leopard Frog, are the most abundant species of anuran on the southeastern US Gulf coast (Erwin et al. 2016). Bayless (1969) showed that Southern Cricket Frogs and A. crepitans Baird (Northern Cricket Frog) avoided interspecific competition through differences in habitat preferences. Although Southern Cricket Frogs prefer ponds like those in our study, Northern Cricket Frogs prefer more extensive wetlands. This preference may be because Southern Cricket Frogs are more selective than Northern Cricket Frogs (Alix et al. 2014, Bayless 1969). However, compared to a wider variety of anuran species, Southern Cricket Frogs are less habitat selective (Chandler et al. 2015). Southern Cricket Frogs are declining throughout the Southeast but increasing in Florida (Villena et al. 2016). Southern Cricket Frogs were the only tree frog species included in this study. Studies have indicated that some populations of Pig Frog are in decline, possibly because of habitat changes (Cassani et al. 2015). Interestingly, Pig Frogs seem to benefit from encroaching development (Delis et al. 1996). This effect may be because they have fairly broad habitat preferences (Delis et al. 1996). Variations in vegetation between different habitats seem to have little effect on Pig Frogs (Chandler et al. 2015); however, permanency of ponds is crucial, since they rarely inhabit ephemeral wetlands (Chandler et al. 2015). Pig Frogs are more uncommon than the other frog species included in this study (Cassani et al. 2015) . Southern Leopard Frogs are true habitat generalists capable of taking advantage of disturbed areas (Alix et al. 2014, Chandler et al. 2015, Delis et al. 1996) and moving widely between various habitats (Pitt et al. 2017). They are often the most abundant species of anuran in wetland areas because they are largely unaffected by vegetation cover or hydroperiod (Chandler et al. 2015, Delis et al. 1996). They have adaptable and diverse behaviors, including a variety of escape methods (Bateman and Fleming 2014). In areas of less vegetation cover, Southern Leopard Frogs tend to remain still but, in areas of high vegetation density, they may flee into thick brush or the water (Bateman and Fleming 2014). Younger frogs tend to remain closer to water for quick escape and vocalize less when fleeing predators (Bateman and Fleming 2014). Southern Leopard Frog occupancy has increased throughout most of the southeastern US, including Florida (Villena et al. 2016), likely due to their adaptability. Anuran species may select different habitats to avoid interspecific competitors (Bayless 1969, Gorman and Haas 2011) and predators (Buxton et al. 2017), or because of their reproductive biology (Gorman and Haas 2011). Predator avoidance and breeding adaptations are linked because amphibian larvae and eggs are Southeastern Naturalist 259 C.M. Bomske and N. Bickford 2019 Vol. 18, No. 2 particularly sensitive to predators (Buxton et al. 2017, Werner and McPeek 1994). Lithobates species can coexist at the same ponds because of resource partitioning (Gorman and Haas 2011). While Southern Leopard Frogs breed through the winter (Lannoo 2005), Pig Frogs are spring and summer breeders (Lamb 1984). Additionally, Pig Frogs chorus from deeper water than Southern Leopard Frogs, which remain closer to the shore (Lamb 1984). Southern Cricket Frogs do not compete with Lithobates directly, but Pig Frogs have been known to prey on hylids, including Southern Cricket Frogs (Ugarte et al. 2007). Therefore, Southern Cricket Frogs probably avoid predatory Lithobates. Microhabitat selection in anurans is important to understanding their ecology and conservation. This study aimed to analyze variations in non-breeding, winter microhabitat and niche selection among 3 species of subtropical American anurans. Field-site Description We performed this study at West Campus (30°23'35''N, 87°25'19''W) of Pensacola Christian College (PCC), a 107-ha (265-ac) private property with recreational facilities for sailing, kayaking, fishing, and other activities. The average winter temperatures is 10–15 °C, but temperatures often rise above 20 °C. Northwest Florida has a humid subtropical climate within the expansive southeastern conifer forests ecoregion. Southern yellow pine forest, comprised of Pinus echinata Mill. (Shortleaf Pine), P. elliottii (Slash Pine), P. palustris Mill. (Longleaf Pine), and P. taeda L. (Loblolly Pine), is the predominant ecosystem. Average annual precipitation is ~1.5 m, but most rainfall occurs during summer’s wet season (hurricanes and tropical storms are common along the Gulf of Mexico’ s coast). The wetland complex at our study site consists of 6 ponds along the shores of Perdido Bay in northwestern Florida (Fig. 1). Pond 1 is the most isolated pond. For most of the year, the narrow channel through pine flatwoods forests is dry but, during storms and wet periods, it drains directly into Pond 2, about 75 m away. Pond 2 drains into Pond 3, but during high water both ponds merge together over the shallow, 10-m, Sphagnum (peat moss)-choked channel connecting them. Pond 3 is the largest pond in the study area but, at its midpoint, a beaver dam partially separates it from Pond 4. Pond 4 drains into Pond 5, which drains into Pond 6. However, Pond 5 and 6 are closer to Perdido Bay and had saltwater intrusions from a hurricane. Therefore, we excluded Ponds 5 and 6 from this study. Pond 1 is 500 m long and 20 m wide, pond 2 is 75 m long and 10 m wide, pond 3 is 50 m long and 10 m wide, and pond 4 is about 90 m long and 50 m wide. All 4 ponds varied greatly in their shape and depth. We identified locations for the study based on transitions in plant assemblages, canopy cover, and the slope of the bank. We organized locations into 7 distinct areas. Area 1 included all of Pond 1 and Area 2 included all of Pond 2. Area 1 was characterized by open, gently sloping, grassy banks with sparse woody plants. Area 2 was characterized by steep banks lined with Slash Pine, Taxodium distichum (Bald-Cypress), and Vaccinium corymbosum (Highbush Blueberry). Area 3 was the northernmost 150 m of Pond 3, Area 4 included the next 200 m southwest of Area Southeastern Naturalist C.M. Bomske and N. Bickford 2019 Vol. 18, No. 2 260 3, and Area 5 was the final, southernmost 150 m of Pond 3. Trees and shrubs were uncommon in Area 3. Emergent species were common because of the increased sunlight. The only common aquatic and emergent plant of Area 5 was Eleocharis spp. (spike rushes; there appears to be more than one species at Pond 3, or else a different species than those commonly found at ponds 1 and 2). The lack of aquatic and emergent vegetation can be attributed to the abundance of Slash Pine. We divided Pond 4 in half, with Area 6 covering the southern half and Area 7 including the northern half. Area 6 had very steep banks. Trees and shrubs were uncommon. Specific plant species and variations in plant community structure at each area are listed in Table 1. Methods We conducted anuran surveys weekly from 17 January 2017 through 24 March 2017. This timing represents winter anuran assemblages. Although many species continue to chorus throughout the summer, this study focused on overwintering anurans at permanent ponds. We avoided the diversity of later choruses of anurans, primarily composed of hylids, by limiting this study to Florida’s winter months. Figure 1. Map of the study areas at West Campus (Google Maps 2018). Study areas are circled by dotted lines and bodies of water are solid white. P1 = Pond 1, P2 = Pond 2, P3 = Pond 3, P4 = Pond 4, P5 = Pond 5, and P6 = Pond 6. Southeastern Naturalist 261 C.M. Bomske and N. Bickford 2019 Vol. 18, No. 2 Anurans chorus most in the evenings after sunset. To avoid biases, we performed surveys regardless of varying weather conditions (cold, rain, humidity, etc.) beginning at sunset and lasting for as long as it took to complete the transect at each pond. We undertook surveys at all West Campus ponds every Friday night for 10 weeks. We collected plant data from April to May 2018, when many species were more conspicuous and easier to identify than at other times. Although vegetative mass increases later in the season, the number of plant of species present at the sites remained approximately the same throughout the duration of this study. We performed surveys around the circumference of every pond, and set as the unit of observation a 2-m wide transect parallel to the corresponding sections of pond shore in each of the 7 survey areas. Ponds were longer than wide and we sampled transects on both sides of the ponds to be as representative as possible. We identified individual anurans primarily through call detection. On most nights, we were able to identify the source of each call, which eliminated duplication bias. On warmer nights, when chorusing was more profuse, identifying individual frogs was difficult. In these cases, we positioned ourselves in the center of each study area and counted as many frogs as possible to produce a sample that Table 1. Plant species richness at the 7 study areas. 2 = common species (present in at least half of all segments surveyed), 1 = uncommon species (present, but in less than half of all segments surveyed), and 0 = absent. Study Area Scientific name Common name 1 2 3 4 5 6 7 Acer rubrum L. Red Maple 0 0 1 0 0 0 0 Andropogon virginicus L. Broomsedge Bluestem 0 1 1 1 2 0 1 Aristida stricta Michx. Wiregrass 0 1 0 0 0 0 0 Centella asiatica (L.) Urb. Spadeleaf 0 1 0 0 0 1 2 Cliftonia monophyla (Lam.) Sarg. Black Titi 1 0 0 0 0 0 0 Dichanthelium sp. Witchgrass 0 0 1 1 2 1 2 Drosera brevifolia Pursh Dwarf Sundew 0 0 0 0 2 0 0 Drosera intermedia Hayne Water Sundew 1 2 2 2 1 1 2 Eleocharis spp. Spikerushes 2 2 2 1 2 1 2 Eriocaulon compressum Lam. Flattened Pipewort 0 0 2 2 2 1 1 Hydrilla verticillata (L.f.) Royle Waterthyme 1 1 2 2 2 2 2 Hydrocotyle bonariensis Comm. ex Lam. Largeleaf Marshpennywort 0 0 0 0 0 0 1 Iva frutescens L. Bigleaf Sumpweed 0 1 0 1 0 0 0 Lachnocaulon anceps (Walter) Morong Whitehead Bogbutton 0 0 0 0 1 0 0 Magnolia grandiflora L. Southern Magnolia 0 0 0 1 0 0 1 Magnolia virginiana L. Sweetbay 0 1 1 0 0 0 1 Morella cerifera (L.) Small Southern Bayberry 0 0 1 1 1 1 1 Panicum sp. Panicgrass 0 2 0 0 0 2 0 Peltandra sagittifolia (Michx.) Morong White Arrow Arum 0 0 1 0 0 0 0 Pinus elliottii Engelm. Slash Pine 2 2 1 2 0 1 1 Sphagnum spp. Peat Mosses 0 0 1 1 2 0 0 Taxodium distichum (L.) Rich. Bald-Cypress 0 1 1 2 1 1 1 Triadica sebifera (L.) Small Popcorntree 0 0 0 0 0 1 0 Utricularia sp. Bladderwort 1 0 0 0 0 0 0 Vaccinium corymbosum L. Highbush Blueberry 0 0 0 2 1 1 1 Vitis rotundifolia Michx. Muscadine 0 0 0 1 1 0 0 Xyris sp. Yelloweyed-grass 1 1 2 1 0 1 1 Species richness 7 12 14 15 13 13 15 Southeastern Naturalist C.M. Bomske and N. Bickford 2019 Vol. 18, No. 2 262 included a minimum number of individuals. On a couple of particularly difficult nights, we averaged 2 or 3 estimates of the minimum number of individuals at each area. We used flashlights and headlamps to detect anurans for visual identification to validate auditory surveys. Captures were rarely necessary. However, if identification of an anuran proved difficult, temporary capture was needed. In particular, Acris gryllus (LeConte) (Southern Cricket Frog) and Acris crepitans Baird (Northern Cricket Frog) are difficult to distinguish. Some species of Lithobates in this region (L. catesbeianus [Shaw] [American Bullfrog], L. clamitans [Latreille] [Green Frog], Pig Frog, L. heckscheri [Wright] [River Frog], etc.) are easily confused when not chorusing, so captures were occasionally required to identify members of this genus, especially early in the study. We employed a variety of nets to aid in capture. There were not always appropriate land paths around ponds, and because identifying individual anurans in a chorus is sometimes difficult from land, we also utilized waders to allow movement around the ponds. We excluded from our counts any frogs that we could not positively identify. We included other species of potential interest if encountered along the transects. Beaver were present at all ponds but we noted them only when seen (sign was excluded). We recorded all sightings as individual data points so that we could determine the frequency that Beavers would be in any given study area, not their presence or absence from an area. We used the same method to count turtles (Trachemys scripta (Thunberg in Schoepff) [Pond Slider]) and snakes (Agkistrodon piscivorus (Lacépède) [Cottonmouth] and Nerodia fasciata (L.) [Banded Water Snake]). Turtles habitually rest just below the water’s surface near the shore at night; thus, they were easy to count. Snakes were active at night, hunting for frogs around shorelines or shallow water. We sampled plant communities along transects correlating with those used for the anuran surveys (see above). We identified plants in each area as common (present in at least half of all 1-m segments of the transect) or uncommon (present in less than half of all 1-m segments of the transect). We measured 1-m–long segments with a marked net handle. We identified all common and uncommon species along pond margins to at least the genus level. We considered species that appeared as isolated specimens in just 1 or 2 of the transects to be inconsequential and we excluded them for this study (a few of these, especially Poaceae, were not identified). We also recorded canopy cover and steepness of the bank at each area. We calculated the proportional frequency of each anuran species (Southern Cricket Frog, Pig Frog, Southern Leopard Frog) and the plant species richness at each of the 7 study areas (n = 7). We conducted 2-sample t-tests to compare anuran frequencies at areas with high canopy cover to those that had little canopy cover (P = 0.5). We also conducted 2-sample t-tests to compare anuran frequencies at steep and gently sloping banks (P = 0.5). We employed Pearson correlations to compare all anuran frequencies with one another, plant species richness, and other recorded species (Beavers, turtles, snakes, fish). Southeastern Naturalist 263 C.M. Bomske and N. Bickford 2019 Vol. 18, No. 2 Results We regularly detected 3 anuran species (Southern Cricket Frog, Pig Frog, Southern Leopard Frog) at each area (Table 2). We recorded a 4th species, Anaxyrus terrestris (Bonnaterre) (Southern Toad), at areas 3, 4, and 5 (n = 6, n = 2, n = 1, respectively) during periods of warmer weather when it entered the ponds for breeding purposes only. We heard a single Hyla squirella Bosc (Squirrel Treefrog) calling at area 5. We excluded both of these species from the anuran data set as nonresident, seasonal species. We also noted possible anuran predators during surveys as we encountered them in the anurans’ habitat (Table 3). We detected Esox niger Lesueur (Chain Pickerel) and Lepomis macrochirus Rafineasque (Bluegill Sunfish) in ponds 1, 2, and 5 and 2, 4, and 5, respectively. We detected Micropterus salmoides (Lacépède) (Largemouth Bass) only in pond 3 and Amia calva L. (Bowfin) in ponds 2 and 3. All 4 of these species are known to eat frogs (Beaty 2017, De Oliveira et al. 2016, Goulet et al. 2016, Lagler and Hubbs 1940). Amphiuma means Garden (Two-toed Amphiuma), a large salamander species that preys on frogs (Schalk et al. 2010), was also present but found in pond 3 only. Other aquatic predators present in the ponds were Cottonmouths (ponds 2, 3, and 4), Banded Water Snakes (ponds 3 and 4), and the Pond Sliders (ponds 2, 3, and 4). We observed Beavers at ponds 2, 3, and 4, but old shavings at pond 1 indicated that they also o ccurred there. There appears to be no relationship between frogs and canopy cover or bank slope on a microhabitat scale (t-test). Pearson correlation analysis revealed a strong negative correlation between Southern Cricket Frogs and Pig Frogs (r = -0.9647), Table 3. Aquatic or semi-aquatic predators of frogs at the study areas. CP = Chain Pickerel, LB = Largemouth Bass, BF = Bowfin, BG = Bluegill, TA. = Two-toed Amphiuma, CM = Cottonmouth, BW= Banded Watersnake, and PS = Pond Slider. Numbers under each species denote the number of individuals detected at each area. Predators Areas CP LB BF BG TA CM BW PS 1 1 0 0 0 0 0 0 0 2 2 1 1 1 0 2 0 1 3 0 0 0 0 1 1 2 6 4 0 1 1 1 1 1 0 6 5 2 0 0 1 0 1 0 0 6 0 0 0 0 0 0 0 4 7 0 0 0 0 0 4 2 1 Table 2. Anuran proportions at the 7 study areas. Species Area 1 Area 2 Area 3 Area 4 Area 5 Area 6 Area 7 Southern Cricket Frog 0.87 0.67 0.71 0.84 0.38 0.57 0.70 Southern Leopard Frog 0.11 0.13 0.19 0.11 0.13 0.14 0.04 Pig Frog 0.02 0.19 0.10 0.05 0.50 0.29 0.26 Plant species richness 13 15 14 12 7 13 15 Southeastern Naturalist C.M. Bomske and N. Bickford 2019 Vol. 18, No. 2 264 but a positive correlation between plant species richness and Southern Cricket Frogs (r = 0.6187; Fig. 2). Consequentially, there was a negative correlation between Pig Frogs and plant species richness (r = -0.5931). Plant species richness also had a positive correlation with snakes (r = 0.5358) and Beavers (r = 0.5253). Southern Leopard Frogs correlated negatively with snakes (r = -.0.5175; Fig. 3) but positively with turtles (r = 0.6853) and Beavers (r = 0.7149; Fig. 4). There was also a strong positive correlation between Beavers and turtles ( r = 0.7685). Discussion Localized variations in habitat have a variety of effects on anuran species frequencies. In contrast to studies conducted at a broader scale (Baskale and Çapar 2016, Porej and Hetherington 2005, Werner et al. 2007), our findings indicate that the slope of a bank and microhabitat canopy cover had little influence on the anuran species in this study. Plant species richness has often been correlated to anuran abundances over broad scales (Cunningham et al. 2007, Sasaki et al. 2015, Shulse et al. 2012) but, on the assemblage level, the trends were less clear (Fig. 2). Figure 2. Southern Cricket Frogs have a strong positive correlation to plant species richness, Pig Frogs have a negative correlation to plant species richness, and Southern Leopard Frogs have no significant correlation to plant species richness. Southeastern Naturalist 265 C.M. Bomske and N. Bickford 2019 Vol. 18, No. 2 The only anuran in this study to correlate positively with plant species richness was the Southern Cricket Frog. Pig Frogs, in contrast, had a negative relationship with vegetation, which is probably a reflection of the tendency of Pig Frogs to sit directly in the water and escape to the water when approached, rather than relying on vegetation for cover (Lamb 1984). In our study, Southern Leopard Frogs did not have any significant relationship with plant species richness; this species has the most adaptable and diverse escape strategies (Bateman and Flemi ng 2014). Our results indicate that predator evasion is the driving force behind anuran and plant associations. This suggestion is confirmed by observed relationships between predator and anuran occurrences. Pig Frogs are known to prey on Southern Cricket Figure 3. Southern Leopard Frogs have a negative correlation with predatory snakes (Cottonmouth and Banded Water Snake). Similarly, Southern Cricket Frogs avoid Southern Leopard Frogs. Figure 2 illustrates this relationship with plant species richness. Figure 4. Pond Slider and Southern Leopard Frog correlations to Beavers. Southeastern Naturalist C.M. Bomske and N. Bickford 2019 Vol. 18, No. 2 266 Frogs and other small hylids (Ugarte et al. 2007). The strong negative correlation between these 2 species is likely a reflection of Southern Cricket Frogs’ avoidance of Pig Frogs, since other studies have indicated that plant species richness has little bearing on either species (Chandler et al. 2015). A future comparison of habitat usage by Southern Cricket Frogs in the absence of Pig Frogs could be revealing. Our finding of a lack of a negative correlation between Southern Cricket Frogs and Southern Leopard Frogs, a potential predator, was unexpected, but could be attributed to a number of habitat elements. Lithobates species seem less sensitive to predators than Southern Cricket Frogs. Although the negative correlation between Southern Cricket Frogs and Pig Frogs was very strong, the only significant negative correlation between Lithobates and a predator was between Southern Leopard Frogs and snakes. Other predators (e.g., turtles, fish) are unlikely to move out of water in search of food, but snakes are more versatile; hence, the avoidance by Southern Leopard Frogs. Curiously, occurrences of predatory fish had no noticeable effects on anuran species abundances. However, all ponds had fish and the presence or absence of fish likely has an effect on anuran abundances (Holbrook and Dorn 2016, Porej and Hetherington 2005). Detecting fish can be challenging and our sampling methods were likely insufficient. Future studies could perform more rigorous comparisons of fish-niche selection and anuran abundances in a connected wetland system. Beavers are ecosystem engineers (Wright et al. 2002), so it should not be surprising that they had an effect on habitat usage in other species. Beavers were strongly correlated with turtles and Southern Leopard Frogs. To a lesser extent, turtles correlated with Southern Leopard Frogs, but these 2 species rarely interact (turtles occasionally consume anurans), indicating that this correlation is a result of both species’ affinity for Beavers. Turtles likely enjoy the open waterways that Beavers create with channels and dams, and Southern Leopard Frogs probably benefit from the habitat heterogeneity closer to shore. Beavers are also associated with higher plant species richness, indicating that they create desirable wetland habitat for a variety of species. The widespread effects of Beavers on a wetland have a positive influence on anuran and other wetland species habitat u sage. Overwintering anuran microhabitat preferences in a network of northwest Florida ponds was influenced by predator avoidance and plant species richness. Behavioral adaptations to threats are unique for each species and, therefore, assemblage preferences were also unique between different species. Our results suggest predator-evasion strategy is a key driver of microhabitat selection in anurans. Acknowledgments We thank M. Bowman and A. Watson for their local expertise on amphibians and plants of northwestern Florida. A. Ahlers’ suggestions throughout the editing process were invaluable. We are grateful to Pensacola Christian College for the use of their facilities for this study. A large part of this research was completed in partial fulfillment of a Master of Science degree at the University of Nebraska at Kearney . Southeastern Naturalist 267 C.M. Bomske and N. Bickford 2019 Vol. 18, No. 2 Literature Cited Adams, C.K., and D. Saenz. 2012. 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