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Seasonal Variation in Composition of Key Largo Woodrat (Neotoma floridana smalli) Diets
Jennifer M. Kanine, Steven B. Castleberry, Michael T. Mengak, and Christopher Winchester

Southeastern Naturalist, Volume 14, Issue 2 (2015): 405–414

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Southeastern Naturalist 405 J.M. Kanine, S.B. Castleberry, M.T. Mengak, and C. Winchester 22001155 SOUTHEASTERN NATURALIST 1V4o(2l.) :1440,5 N–4o1. 42 Seasonal Variation in Composition of Key Largo Woodrat (Neotoma floridana smalli) Diets Jennifer M. Kanine1, Steven B. Castleberry1,*, Michael T. Mengak1, and Christopher Winchester1,2 Abstract - Neotoma floridana smalli (Key Largo Woodrat) is currently at high risk of extinction from anthropogenic disturbances, including loss and degradation of habitat and non-native predators. Habitat degradation may affect food-resource availability, yet food habits are poorly understood. Therefore, we examined seasonal diets of Key Largo Woodrats using microhistological analysis of fecal samples. We collected fecal material from captured individuals between January 2005 and February 2006 and identified food items to the lowest possible taxon. We classified food items as leaves, fruit, and insects to examine differences in diets between seasons (wet versus dry) and sexes. Fruit and leaves made up a greater percentage of Key Largo Woodrat diets during the wet and dry seasons, respectively, likely reflecting higher fruit availability during the wet season. Across seasons, diets of males had a higher percentage of fruit and insects, but a lower percentage of leaves than females. Greater fruit consumption by males, which may be related to their higher motility, was contrary to our expectations that females would consume more fruit to meet the nutritional demands of reproduction. Although fruit and leaves are both important components of Key Largo Woodrat diets, consumption varies seasonally likely in response to differences in availability. Introduction Neotoma floridana smalli Sherman (Key Largo Woodrat) is one of 5 subspecies of Neotoma floridana Ord (Eastern Woodrat) that occur throughout the southeastern US (Whitaker and Hamilton 1998). The species is endemic to the tropical hardwood hammocks of Key Largo, FL, and its geographic range is separated from that of other Eastern Woodrat subspecies by at least 210 km (Greer 1978). The Key Largo Woodrat was federally listed as endangered in 1984 due to habitat loss from development and agriculture (USDI 1999). The population has been confined to a remnant forested habitat encompassing approximately 850 ha on the northern end of the island since 1973 (Barbour and Humphrey 1982), over 90% of which is protected as federal- and state-managed lands (Frank et al. 1997). Population viability analysis conducted by McCleery et al. (2005) predicted a >70% chance of extinction within 10 years without management due to small population size, non-native predators (Winchester et al. 2009), and the possibility of continued development surrounding the protected area (USDI 1999). 1Warnell School of Forestry and Natural Resources, University of Georgia, Athens, GA 30602. 2Current address - Florida Fish and Wildlife Conservation Commission, 3911 Highway 2321 Panama City, FL 32409. *Corresponding author - Manuscript Editor: Karen Powers Southeastern Naturalist J.M. Kanine, S.B. Castleberry, M.T. Mengak, and C. Winchester 2015 Vol. 14, No. 2 406 Anthropogenic disturbance degraded remaining Key Largo Woodrat habitat (USDI 1999), likely altered food resource availability, and may have caused negative fitness consequences (Randolph et al. 1977). Spatial and temporal variation in food availability can affect reproduction in small mammals (Gittleman and Thompson 1988, Hansen and Batzli 1978, Millar 1981, Nichols et al. 1976). For example, limited food resources in some seasons may lower reproductive output in Sigmodon hispidus Say and Ord (Hispid Cotton Rat) by reducing food intake and body mass to minimal levels (Randolph and Cameron 2001). Female Hispid Cotton Rats draw on stored energy reserves when food quality and quantity are inadequate or foraging conditions are suboptimal; this situation may decrease their ability to reproduce in the future (Randolph et al. 1977). Adverse environmental conditions also can cause reductions in the number of young/litter in some small mammals (McClure 1981, Millar 1975, Sikes 1995). For example, poor nutritional quality in the diet of Microtus californicus Peale (California Vole) has been linked to reduced litter sizes (Batzli 1986). In addition, insufficient food resources may force adults to forage farther from nest sites and for longer duration, subjecting them to increased predation risk (Wood 2008). Many small mammals exhibit seasonal peaks in reproduction tied to resource availability (Reilly et al. 2006). Key Largo Woodrats, similar to other Eastern Woodrat subspecies, exhibit breeding-activity peaks during spring and summer, with the greatest number of lactating females occurring between July and September (Hersh 1981). In other small mammals, such as Hispid Cotton Rats and Lasiopodomys brandtii Radde (Brandt’s Vole), lactating females have higher energy requirements (Liu et al. 2003, Millar 1975, Randolph et al. 1977) and ingest plant species in different proportions than non-reproductive females and males (Randolph et al. 1991). Therefore, diets of reproductive female Key Largo Woodrats are likely to reflect different resource requirements than non-reproductive females or m ales. Information on how food-resource requirements relate to Key Largo Woodrat abundance and distribution is needed to determine appropriate management actions (USDI 1999). However, information regarding types of foods consumed is limited and based primarily on food remains in nests and from preferences of captive individuals (Hersh 1978). Furthermore, seasonal variation in diets is unknown. Therefore, our objectives were to identify food items consumed by Key Largo Woodrats using microhistological analysis of fecal samples and determine how plant species composition in diets differs between sexes and seasons. Field-Site Description Our study was conducted on Key Largo, the largest and most northern of the Florida keys. The study area consisted of ~850 ha on Crocodile Lake National Wildlife Refuge (25°16'16''N, 80°19'15''W) and Dagny Johnson Key Largo Hammock Botanical State Park (25°10'38''N, 80°21'5''W). The upland forests of the area, described as hardwood hammocks, are comprised primarily of closed-canopy, evergreen, broad-leaved trees growing on a limestone substrate (Ross et al. 1992, Snyder et al. 1990). Hardwood hammocks are one of the most species-rich forests Southeastern Naturalist 407 J.M. Kanine, S.B. Castleberry, M.T. Mengak, and C. Winchester 2015 Vol. 14, No. 2 in North America, with over 150 known tree and shrub species (Ross et al. 1992), and those on Key Largo currently exist in a variety of seral stages due to past natural and anthropogenic disturbance. The climate is warm with mean daily temperatures ranging from 17 to 25 °C (Obeysekera et al. 1999). Seasons are defined primarily by rainfall patterns: the wet season lasts ~7 months from spring through summer, and the dry season consists of ~5 months from fall through winter (Duever et al. 1994, Obeysekera et al. 1999). Methods We collected fecal samples for microhistological food-habits analysis from Key Largo Woodrats captured from January 2005 to February 2006 on 21 trapping grids in areas representing a variety of hammock ages. Trapping grids consisted of 9 stations in a 3 x 3 array with 25-m spacing between stations. At each station, we placed 2 vented Sherman traps (10.2 x 11.4 x 38.1 cm; H.B. Sherman Traps, Inc., Tallahassee, FL) with Procyon lotor L. (Northern Raccoon)-proof door latches and baited them with peanut butter and crimped oats. As a part of ongoing studies (Winchester et al. 2009, 2011), we trapped grids a total of 3 times during the study period (once each during April–May, August–September, and November–December) and opportunistically between and after the primary trapping periods. For each trapping session, We opened the traps at dusk and checked them daily within the first 3 hours after sunrise for 4 consecutive days. We sexed, weighed, marked with passive integrated transponder (PIT) tags (Biomark, Boise, ID; Gibbons and Andrews 2004) and #1005 Monel ear tags (National Band and Tag Company, Newport, KY), and released all captured individuals at the capture location. After removing the entrapped animals, we placed fresh fecal samples from the traps into individual vials for freezing until microhistological analysis was conducted; samples were collected from individuals only once within a 4-night sampling session even if a particular animal was captured multiple times. We conducted animal capturing and handling under Federal Fish and Wildlife Endangered Species Permit # TE0959080-1, State of Florida Fish and Wildlife Conservation Commission Special Purpose Permit # WX05089, Florida Department of Environmental Protection Research and Collection Permit # 5-05-41, and University of Georgia Animal Care and Use Permit # A2005-10044-0. The Washington State University Wildlife Habitat and Nutrition Laboratory (Pullman, WA) conducted microhistological food-habits analysis. We prepared reference slides to aid in food-item identification using potential plant-food items collected from the study area each season; insect reference material was not collected. We followed the techniques of Davitt and Nelson (1980) to prepare permanent reference-slide mounts for comparison to items found in feces. We determined the botanical composition of fecal samples using a modification of the frequency–density-conversion sampling procedures from Flinders and Hansen (1972), Holechek and Gross (1982), Holechek and Vavra (1981), and Sparks and Malechek (1968). After homogenizing the material, we prepared 2 slides from each fecal sample collected. Using a 10 x 10 square grid mounted in the eyepiece of the microscope, we visually estimated the area (number of Southeastern Naturalist J.M. Kanine, S.B. Castleberry, M.T. Mengak, and C. Winchester 2015 Vol. 14, No. 2 408 grid boxes) of each positively identified plant cuticle and epidermal fragment observed in 25 randomly located microscope views on individual slides (50 total views per sample). We estimated the area covered by each taxon at 100x magnification, but increased magnification (200x to 450x) to aid in identification of fragments (Holechek and Valdez 1985). We recorded the area covered by each plant fragment and combined measurements by species or the lowest taxon possible. We identified insect fragments only as insect. We determined percent composition of individual food items in each sample by dividing the total area cover of each item by the total area cover of all items and multiplying the product by 100. We calculated mean frequency of occurrence as the number of diet samples in which a food item was found divided by the total number of samples multiplied by 100. We calculated mean number of food items/sample for all samples. We identified all plant taxa with mean percent diet composition >2% and mean frequency of occurrence >20% and summarized data by food item type (leaf, stem, fruit, or insect) and plant-growth form (cactus, herbaceous, shrub, tree, or vine). We combined leaves and stems (hereafter, leaves) because mean percent composition of stems in the diet was less than 1% across all diets. We divided the trapping period into 2 time periods corresponding to the wet (May–November) and dry (December–April) seasons. We determined differences in percent diet composition of food-item types (leaves, fruit, and insects) between seasons and sexes using analysis of variance (ANOVA) and post hoc Tukey’s honest significant difference (HSD) test. Percentage data for leaves, fruit, and log-transformed insects were converted to proportions and arcsine square-root transformed (Sokal and Rohlf 1981) for analysis. We conducted analyses using SAS 9.1 (SAS Institute, Inc., Cary, NC) and accepted statistical significance at P ≤ 0.05. Results Fecal samples were collected from 60 Key Largo Woodrats captured during the study, including 31 females (16 in the dry season, 15 in the wet season) and 29 males (9 in the dry season, 20 in the wet season). Leaves and fruits comprised 51.6% and 42.1%, respectively, of Key Largo Woodrat diets across seasons and sexes. The percent of insects in the diet was relatively low compared to plants, comprising less than 6.3% of the species’ diet across seasons and sexes. We identified 46 plant taxa, including leaves and fruits of 41 and 19 taxa, respectively (Appendix 1). Plant taxa consisted of 31 trees, 8 shrubs, 4 vines, 2 herbaceous plants, and 1 cactus. Most leaves identified in diets were from shrubs and trees (73%), and most fruits were from trees (65%). Of the 46 plant taxa identified, Key Largo Woodrats consumed only leaves from 22, only fruits from 5, and both fruit and leaves from 19. Twelve taxa comprised a mean percent diet composition of >2% and mean frequency of occurrence >20% (T able 1). We found no interactions (leaves: F1,56 = 1.75, P = 0.19; fruits: F1,56 = 3.48, P = 0.07; insects: F1,41 = 0.01, P = 0.91) between seasons and sexes in percent diet composition for any of the food item types examined. Key Largo Woodrats (males Southeastern Naturalist 409 J.M. Kanine, S.B. Castleberry, M.T. Mengak, and C. Winchester 2015 Vol. 14, No. 2 and females combined) consumed more fruits during the wet season (F1,56 = 5.90, P = 0.02) and more leaves (F1,56 = 8.22, P = 0.006) during the dry season (Table 2). Across seasons, females consumed more leaves (F1,56 = 10.68, P = 0.002) but fewer fruits (F1,56 = 7.91, P = 0.007) and insects (F1,41 = 5.68, P = 0.02) than males. We found no difference (F1,56 = 0.37, P = 0.55) in percent diet composition of insects between seasons for both sexes combined. Table 1. Key Largo Woodrat plant-food items with mean percent diet composition (comp.; area of each food item in microscope field of view/area of all food items x 100) >2% and frequency of occurrence (occur.; number of samples in which a food item was found/total number of samples x 100) >20% identified using microhistological analysis of fecal samples collected on Key Largo, FL, 2005–2006. Growth Food Scientific name Common name form type Comp. Occur. Psychotria ligustrifolia (Northrop) Bahama Coffee Shrub Leaves 14.8 80.0 Eugenia sp. Stopper Tree Fruit 6.6 58.3 Lantana sp. Lantana Shrub Leaves 3.4 56.7 Zanthoxylum flavum (Vahl) Yellowwood Tree Fruit 5.4 55.0 Ficus sp. Fig Tree Fruit 7.1 50.0 Bursera simaruba (L.) Sargent Gumbo-limbo Tree Leaves 2.8 46.7 Coccoloba sp. Pigeon Plum Tree Leaves 5.1 38.3 Leucaena leucocephala (Lamarck) Lead Tree Tree Leaves 2.7 38.3 de Wit Psychotria ligustrifolia (Northrop) Bahama Coffee Shrub Fruit 3.2 28.3 Millspaugh Zanthoxylum flavum (Vahl) Yellowwood Tree Leaves 2.4 26.7 Pithecellobium sp. Blackbead Tree Fruit 2.3 25.0 Passiflora multiflora (L.) Whiteflower Passionflower Herb Leaves 4.1 23.3 Table 2. Mean (± SE) percent diet composition (area of each food item in microscope field of view/ area of all food items x 100) of leaves, fruits, and insects in diets of male and female Key Largo Woodrats during the wet and dry seasons on Key Largo, FL, 2005–2006. Mean values with the same superscript are statistically different (P ≤ 0.05). Season Wet Dry Overall (n = 35) (n = 25) (n = 60) Male (n = 29) Leaves 37.1 ± 6.6 45.5 ± 7.3 39.7 ± 5.1A Fruit 52.0 ± 6.5 50.2 ± 7.2 51.5 ± 4.9B Insect 10.9 ± 3.0 4.3 ± 1.9 8.8 ± 2.2C Female (n = 31) Leaves 48.7 ± 7.3 76.0 ± 5.1 62.7 ± 5.0A Fruit 46.5 ± 6.3 21.1 ± 4.9 33.4 ± 4.5B Insect 4.8 ± 2.0 3.0 ± 0.9 3.9 ± 1.1C Overall (n = 60) Leaves 42.0 ± 5.0D 65.0 ± 5.1D 51.6 ± 3.9 Fruit 49.7 ± 4.5E 31.6 ± 4.9E 42.1 ± 3.5 Insect 8.3 ± 2.0 3.5 ± 0.9 6.7 ± 1.2 Southeastern Naturalist J.M. Kanine, S.B. Castleberry, M.T. Mengak, and C. Winchester 2015 Vol. 14, No. 2 410 Discussion Leaves and fruits each composed approximately half of Key Largo Woodrat annual diets, but consumption varied between seasons and sexes. Seasonal diet variation is common in generalist mammals and may result from differences in availability among seasons (Alves-Costa et al. 2004, Kincaid and Cameron 1982). Although fruits are likely preferred when available, leaves are abundant in both seasons (Bancroft et al. 2000) and allow Key Largo Woodrats to meet their year-round nutritional demands. Higher overall percent consumption of leaves during the dry season apparently compensated for lower fruit abundance (Bancroft et al. 2000). Higher overall percent fruit consumption by males was contrary to our expectation that females would consume more fruit due to their higher nutritional demands (Millar 1981, Randolph et al. 1977). Although temporal differences were not statistically different, percent fruit in male diets during the dry season appeared to account for their overall higher fruit consumption. Average home-range size for males is bigger than that for females during spring and summer (>7 times larger) and fall (>1.5 times larger) (Mc- Cleery et al. 2006). By searching a larger area than females, males may be better able to acquire fruit during the dry season when less is available. Although not quantified in our study, the observed pattern of fruit consumption likely reflects availability. Bancroft et al. (2000) examined fruit availability in the Florida Keys and determined that relative availability was higher between May and September, which supported our observation of higher fruit consumption during the wet season. Fleshy fruits, such as those found on our study area, are similar in nutrient quality and digestibility to acorns (Short and Epps 1976), which are a primary food source for other woodrat species (Castleberry et al. 2002, Horton and Wright 1944, Mengak and Castleberry 2008, Poole 1940). Thus, fruit likely represents a preferred food item that is consumed in high quantities by Key Largo Woodrats when available. Insects are important food sources for several rodent species, including Peromyscus leucopus Rafinesque (White-footed Mouse), P. maniculatus Wagner (American Deer Mouse), and Sciurus carolinensis Gmelin (Eastern Gray Squirrel) (Hamilton 1941, Nixon et al. 1968, Whitaker 1966). We found a low percent occurrence of insects compared to fruits and leaves in Key Largo Woodrat diets. Similarly, Castleberry et al. (2002) documented low occurrence of insects compared to other food items in Neotoma magister Baird (Allegheny Woodrat) diets in West Virginia. Softbodied arthropods are highly digestible and therefore are likely underrepresented in post-digestion diet-analysis results (Castleberry et al. 2002). The apparent greater consumption of insects by males we observed may be a spurious result of the small percentage of insects in the diets or some unknown factor. Key Largo Woodrats are habitat generalists (Winchester et al. 2011) that use a variety of woody plants and food types to meet dietary requirements. Fruit and leaves are both important diet components and consumption varies seasonally, which is likely driven by higher fruit availability during the wet season (Brancroft et al. 2000).Management to provide a variety of important food plants identified in this study throughout the available habitat on Key Largo should be a consideration in conservation planning for the species. Southeastern Naturalist 411 J.M. Kanine, S.B. Castleberry, M.T. Mengak, and C. Winchester 2015 Vol. 14, No. 2 Acknowledgments Funding, equipment, and housing were provided by the USDI Fish and Wildlife Service. Dagny Johnson of Key Largo Hammock Botanical State Park provided access and logistical support. We thank J. Beerens, T. Bornham, E. Saunders, C. Degayner, R. Degayner, S. Klett, M. McElroy, M. Merril, B. Muiznieks, T. Petersen, and S. 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Peles and J. Wright (Eds.). The Allegheny Woodrat: Ecology, Conservation, and Management of a Declining Species. Springer, New York, NY. 231 pp. Southeastern Naturalist J.M. Kanine, S.B. Castleberry, M.T. Mengak, and C. Winchester 2015 Vol. 14, No. 2 414 Appendix 1. Food type and growth form of plants identified in microhistological analysis of Key Largo Woodrat fecal samples collected on Key Largo, FL, 2005–2006. * indicates plants and food types with percent diet composition (area of each food item in microscope field of view/area of all food items x 100) >2% and frequency of occurrence (number of samples in which a food item was found/total number of samples x 100) >20%. Scientific name Common name Food type Growth form Acanthocereus tetragonus (Hummelinck) Barbed-wire Cactus Fruit/leaf Cactus Ardisia escallonioides (Schlechtendal Marlberry Fruit/leaf Tree & Chamisso) Bourreria succulenta (Jacquin) Bahama Strongbark Fruit Tree Bursera simaruba (L.) Sargent Gumbo-limbo Leaf* Tree Calyptranthes sp. Myrtle-of-the-river Leaf Tree Canella winterana (L.) Gaertner Cinnamon-bark Fruit/leaf Tree Capparis cynophallophora (L.) Jamaica Caper Leaf Tree Casasia clusiifolia (Jacquin) Urban Seven-year Apple Fruit/leaf Tree Chiococca alba (L.) Hitchcock Snowberry Leaf Shrub Chrysophyllum oliviforme (L.) Satinleaf Leaf Tree Coccoloba sp. (Browne) Pigeon plum Fruit*/Leaf Tree Conocarpus erectus (L.) Buttonwood Leaf Tree Crossopetalum sp. Christmasberry Leaf Tree Dipholis salicifolium (L.) A. de Candolle Willow Bustic Leaf Tree Drypetes sp. Milkbark Leaf Tree Eugenia sp. Stopper Fruit*/leaf Tree Exostema caribaeum (Jacquin) Schultes Princewood Leaf Tree Exothea paniculata (Jussieu) Walpers Inkwood Leaf Tree Ficus sp. Fig Fruit*/leaf Tree Guapira discolor (Sprengel) Little Blolly Fruit/Leaf Tree Guettarda sp. Velvetseed Fruit/Leaf Tree Gymnanthes lucida (Swartz) Crabwood Leaf Tree Hamelia patens (Jacquin) Firebush Fruit/leaf Shrub Lantana sp. Lantana Fruit/leaf* Shrub Leucaena leucocephala (Lamarck) de Wit Lead tree Leaf* Tree Myrsine cubana (A. de Candolle) Colicwood Leaf Tree Passiflora multiflora (L.) Whiteflower passionflower Fruit/Leaf* Vine Passiflora suberosa (L.) Corkystem Passion Flower Fruit/Leaf Vine Pentalinon luteum (L.) B.F. Hansen Wild Allamanda Leaf Vine & Wunderlin Piscidia piscipula (L.) Sargent Jamaica Dogwood Leaf Tree Pithecellobium sp. Blackbead Fruit* Tree Psychotria ligustrifolia (Northrop) Bahama coffee Fruit*/leaf* Shrub Randia aculeata (L.) Indigoberry Fruit/leaf Tree Reynosia septentrionalis (Urban) Darling Plum Leaf Tree Rivina humilis (L.) Rouge Plant Fruit/leaf Herb Sapindus saponaria (L.) Soapberry Leaf Tree Schaefferia frutescens (Jacquin) Florida Boxwood Leaf Shrub Simarouba glauca (de Candolle) Paradise Tree Fruit/leaf Tree Smilax auriculata (Walter) Earleaf Greenbrier Leaf Vine Solanum sp. Solanum Fruit/leaf Shrub Sophora tomentosa (L.) Yellow Necklace Pod Leaf Shrub Swietenia mahagoni (L.) Jacquin West Indian Mahogany Fruit Tree Tamarindus indica (L.) Tamarind Fruit Tree Trema sp. Trema Leaf Shrub Vitus sp. Vitus Fruit Vine Zanthoxylum flavum (Vahl) Yellowwood Fruit*/leaf* Tree