Food habits of a small Florida black bear population in an

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Food habits of a small Florida black bear population in anendangered ecosystemAuthors: Sean M. Murphy, Wade A. Ulrey, Joseph M. Guthrie, David S. Maehr,Warren G. Abrahamson, et. al.Source: Ursus, 28(1) : 92-104Published By: International Association for Bear Research and ManagementURL: https://doi.org/10.2192/URSU-D-16-00031.1

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Food habits of a small Florida black bear population inan endangered ecosystem

Sean M. Murphy1,3,4, Wade A. Ulrey1,5, Joseph M. Guthrie1,6, David S. Maehr1,7,Warren G. Abrahamson2, Sutton C. Maehr1,8, and John J. Cox1

1Department of Forestry, University of Kentucky, Lexington, KY 40546, USA2Department of Biology, Bucknell University, Lewisburg, PA 17837, USA

Abstract: The Highlands–Glades subpopulation (HGS) of Florida, USA, black bears (Ursus ameri-canus floridanus) is small, genetically depauperate, and resides primarily within the endangered LakeWales Ridge ecosystem, which has lost >85% of native habitat to land development. Habitat loss canreduce availability of critical natural foods and cause bears to increase reliance on anthropogenic foods(i.e., human-sourced); lands supporting the HGS are expected to lose >50% of remaining Floridablack bear habitat in coming decades. We used scat analysis to describe seasonal food habits, inves-tigate potential dietary responses to food shortages, and inform habitat conservation and human–bearconflict management. Florida black bears in the HGS mostly relied on native soft and hard mast andinvertebrates, which are all available in endangered scrub habitat communities. Corn dispensed athunter-operated feeding stations was a dominant food item in scats; and other alternative foods, suchas citrus fruit and white-tailed deer (Odocoileus virginianus), were found in summer-collected scatswhen soft mast should have been prevailing. Results indicate bears may respond to soft mast shortagescaused by mast failures or habitat loss by consuming anthropogenic foods (e.g., corn, deer chow, citrusfruit, and garbage), which could increase human–bear conflicts. Florida carpenter ants (Camponotusfloridanus) appeared to provide a reliable compensatory food during such shortages, but they are ar-boreal and largely dependent on imperiled bear habitat for proliferation. We strongly suggest remnantscrub and other communities rich in soft and hard mast-producing flora be targeted for acquisitionand protection to ensure persistence of Florida black bears in this diverse ecosystem. We also suggestnon-lethal actions to mitigate bear habituation to anthropogenic foods be implemented to minimizehuman–bear conflicts and prevent unnecessary losses to the already small HGS. Our study should berepeated to investigate whether dietary shifts occur in response to impending habitat loss and to furtherinform population conservation, habitat protection, and conflict management.

Key words: anthropogenic, diet, Florida, Florida black bear, food habits, habitat fragmentation, habitat loss, human–bear conflict, Lake Wales Ridge, Ursus americanus floridanus

DOI: 10.2192/URSUS-D-16-00031.1 Ursus 28(1):92–104 (2017)

Widespread habitat destruction caused by urban devel-opment, agriculture expansion, and other anthropogenic

3email: [email protected] address: Carnivore Program, New MexicoDepartment of Game and Fish, Santa Fe, NM 87507, USA5Present address: The Nature Conservancy, Swanton, OH43558, USA6Present address: Nelson Byrd Woltz Landscape Architects,Charlottesville, VA 22902, USA7Deceased8Present address: Large Carnivore Program, LouisianaDepartment of Wildlife and Fisheries, Baton Rouge, LA70898, USA

land uses subdivided a formerly contiguous statewideFlorida black bear (Ursus americanus floridanus) popula-tion into 7 disjunct subpopulations with varying levels ofconnectivity among them (Dixon et al. 2007). State-levelprotection and habitat restoration efforts facilitated abun-dance increases and some range reoccupation by mostFlorida black bear subpopulations during the past decade(Humm et al. 2017). However, results from a recentnon-invasive genetic spatial capture–recapture study thatused sampling and analytical methods similar to thoseused by Murphy et al. (2016) indicated the Highlands–Glades subpopulation (HGS) in south-central Florida,USA, remains small (N = 98 bears) and genetically de-pauperate (effective population size [NE] = 25 bears;

92


BEAR FOOD HABITS IN AN ENDANGERED ECOSYSTEM � Murphy et al. 93

S. M. Murphy and W. A. Ulrey, unpublished data). Theprimary limiter to population growth and genetic recov-ery of the HGS is habitat availability (Maehr et al. 2004,Florida Fish and Wildlife Conservation Commission[FWC] 2012).

The HGS is supported by a mosaic of native habi-tat communities that are disjunctly arranged in the en-dangered Lake Wales Ridge ecosystem and adjacent ar-eas across a primarily agricultural and urban landscape(Pearlstine et al. 1997, Maehr et al. 2004, Weekley et al.2008; Fig. 1). This includes federally endangered scrubcommunities that support numerous endemic and imper-iled flora and fauna (U.S. Fish and Wildlife Service [US-FWS] 1999). Although a hotspot for biodiversity (Nosset al. 2015), the endangered Lake Wales Ridge ecosys-tem has experienced a >85% area loss of native com-munities (Weekley et al. 2008), and lands occupied bythe HGS constitute one of the most fragmented areas inNorth America with an established black bear popula-tion (Maehr et al. 2001, 2004). Nonetheless, the HGShas the potential to serve as a stepping stone that facili-tates demographic and genetic connectivity between thesouthern-most Big Cypress subpopulation and all otherFlorida black bear subpopulations to the north (Dixonet al. 2007; Fig. 1 inset). Central Florida is, however,expected to incur substantial anthropogenic developmentand the largest percentage of habitat loss (>50%) in thestate in coming decades (Carr and Zwick 2016), and in-tervening habitat between those subpopulations is threat-ened by rising sea levels from climate change (Whittle2009, Carr and Zwick 2016).

Contrary to all other Florida black bear subpopula-tions, management of the HGS has relied almost exclu-sively on anecdotal information (FWC 2012). A lackof scientific knowledge about HGS bear ecology hasthwarted conservation efforts (Maehr et al. 2004) andthus possibly hindered resiliency of the HGS to impend-ing habitat loss. Food habits studies are an important ini-tial step toward a more comprehensive understanding ofecological relationships of bear populations (Beckmannand Berger 2003, Lesmerises et al. 2015, Costello et al.2016). For small or imperiled bear populations, such in-vestigations may be vital for informing landscape-levelconservation planning (Fortin et al. 2013, Ciucci et al.2014). Although habitat productivity and therefore foodavailability change dynamically because of natural eco-logical processes (e.g., transitions between seasons), an-thropogenic land-use activities can permanently degradeimportant habitats and decrease availability of criticalnatural foods. Dietary studies can facilitate monitoringof bear population responses to landscape-level changes

such as dietary shifts and increased reliance on human-sourced foods (Hopkins et al. 2014, Ditmer et al. 2016),and inform habitat and population conservation in areaswhere the loss of critical habitat is an imminent threat tolong-term population persistence.

Limited availability or accessibility of natural foodsbecause of habitat quality and quantity issues can in-crease the probability that bears exploit anthropogenicfoods (Benson and Chamberlain 2006, Merkle et al. 2013,Ditmer et al. 2016), which are human-sourced foodsmade available to bears via human activities (e.g., agricul-ture, hunting, and urban development; Oro et al. 2013).Consumption of anthropogenic foods by bears is asso-ciated with human–bear conflicts; therefore, food habitsstudies can also inform conflict management (Greenleafet al. 2009, Hopkins et al. 2014). Human–black bear con-flicts increased rapidly throughout Florida over the pastdecade, particularly in the central portion of the statewhere multiple bear attacks on humans occurred in recentyears, which prompted the state wildlife managementagency to increase bear euthanasia in urban and exurbanareas and implement a controversial legal harvest (FWC2015). Although those are oft-employed agency man-agement responses to chronic conflicts (Agee and Miller2009, Penteriani et al. 2016), similar actions applied tothe HGS could further reduce the number of black bearsin this already small subpopulation.

To address said issues and provide managers withscience-based information on HGS black bear ecology,we conducted a food habits study in which we collectedand analyzed Florida black bear scats over a 2-year pe-riod. We also investigated whether a lack of natural foodsin bear scats was associated with an increased occur-rence of anthropogenic foods in scats. Our rationale wasthat, in the absence of direct measurements of naturalfoods availability (e.g., rigorous mast surveys; Ryan et al.2007), an apparent replacement of natural foods with an-thropogenic foods may suggest limited availability oraccessibility of the former (Greenleaf et al. 2009, Merkleet al. 2013, Hopkins et al. 2014). Collectively, findingsfrom our study should be useful for habitat and subpop-ulation conservation efforts and for human–bear conflictmanagement in the HGS.

Study areaThe 998-km2 primary range of the HGS (Simek et al.

2005; Fig. 1) is located in Highlands and Glades coun-ties of south-central Florida, where the climate is humidsub-tropical with hot, wet summers and mild, dry winters.Average elevation is 47 m above sea level, average annual

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94 BEAR FOOD HABITS IN AN ENDANGERED ECOSYSTEM � Murphy et al.

Fig. 1. Available habitat and primary range (Simek et al. 2005) of the Highlands–Glades subpopulation ofFlorida black bears (Ursus americanus floridanus) in south-central Florida, USA, where 166 bear scats werecollected during 2004–2006 to describe food habits.

temperature is 21.2◦C, and average annual precipitation is136 cm (Archbold Biological Station 2010). Native hardmast–producing trees include the Florida-endemic scrubhickory (Carya floridana) and 7 species of oak (Quercusspp., including the Florida-endemic Q. inopina). Domi-nant soft mast-producing shrubs and plants are saw pal-metto (Serenoa repens), Florida-endemic scrub palmetto(Sabal etonia), blueberry (Vaccinium spp.), and black-berry (Rubus spp.; Abrahamson et al. 1984).

Approximately 36% (359 km2) of lands within HGSprimary range are considered potential Florida black bearhabitat (Fig. 1). Many lands within primary range havebeen converted to agriculture (41%; 409 km2), primarilycitrus groves (12%; 120 km2) and open pasture (23%; 230km2; FWC 2014). Twelve percent (120 km2) of primaryrange has been developed as urban areas (FWC 2014);average human population density is 37 people/km2 andthe largest city is Sebring (10,331 people). Numerous

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freshwater lakes and wetlands represent the remainingland area within primary range (11%; 110 km2).

MethodsField sampling, scat classification, and fooditems identification

From May 2004 to April 2006, we collected Floridablack bear scats opportunistically along roads and trails,at locations where bears were live-captured as part of a re-source use study (Ulrey 2008, Guthrie 2012), and whereotherwise we had permission to access bear-occupiedlands (Fig. 1). We placed each collected scat in a sealedplastic bag labeled with the date of collection and Univer-sal Transverse Mercator coordinates, and froze samples≤4 hours post-collection. Scats decomposed rapidly inthe hot, humid, and wet study area (W. A. Ulrey and J. M.Guthrie, personal observation); therefore, we presumedall collected scats reflected the month of defecation.

We classified scats into 3 seasonal periods that corre-sponded to Florida black bear biology and natural foodsavailability (FWC 2012): winter–spring (Jan–Apr), en-compassing hypophagia when parturient females denand also when den emergence occurs; summer (May–Aug) during breeding season and soft mast ripening;and autumn (Sep–Dec) when hard mast becomes avail-able and bears exhibit hyperphagia. We combined winterand spring into a single period because sample sizes forboth seasons were independently small (n < 20 scatseach season/yr) and because radiomonitoring data (n =64 bears; 2004–2009) indicated many male and non-parturient female bears were winter-active (Ulrey 2008,Guthrie 2012).

We thawed and rinsed each scat through a single sieve(1.5-mm mesh) and then mixed the contents. We did notsubsample for our analyses (e.g., Ciucci et al. 2014), butinstead evaluated each scat in its entirety, hand-separatingmacro-categories (e.g., grasses, seeds, hair, and bones).We sorted and identified all food items to the lowest tax-onomic resolution possible using field guides and iden-tification manuals (e.g., Martin and Barkley 1961, Bor-ror and White 1970, Peterson 1999, Marshall 2006). Weidentified seeds by comparing them with a reference col-lection from the study area (Archbold Biological Station,Venus, Florida, USA), and examined mammal hairs asmedulla slides that depicted the outside structures of hairunder a 40 × microscope and classified them to speciesusing keys and reference collections from the study area(Archbold Biological Station). We identified arthropodsto taxonomic order and to genus or species when possible;identifications were verified by a professional entomolo-

gist who was familiar with species in the study area (M.A. Deyrup, Archbold Biological Station). We classifiedall vegetation items (e.g., leaves, grasses, and forbs) intoa single category (i.e., vegetation) because they typicallyhave similar nutritional value (Dahle et al. 1998, Klareet al. 2011). We discarded black bear hair, which waspresumably ingested by bears when grooming.

Data analysesSeasonal sample sizes within a bear-year (i.e., May

2004–Apr 2005 and May 2005–Apr 2006) were rela-tively small, so we pooled season-specific data from bothyears. Most previous Florida black bear studies only usedfrequency of occurrence (FO) to describe food habits(Maehr et al. 2001), and an objective of our study was tocompare food habits among subpopulations. Frequencyof occurrence is also particularly appropriate for inves-tigating diet diversity (Bojarska and Selva 2012), whichwas of importance for the HGS because of impendinghabitat loss and the associated potential decline of natu-ral foods. Therefore, we calculated seasonal FO of eachfood item at the lowest identifiable taxon and seasonalFO of major food categories using the same method usedby Ciucci et al. (2014) and Larson et al. (2015). We com-pared FO of the major food categories (soft mast, hardmast, invertebrates, vertebrates, vegetation, and anthro-pogenic) across seasons using a χ2 test (Stenset et al.2016). Data pooling was necessary, so we averaged FOsamong seasons and calculated standard deviation as ameasure of variance to provide a more reliable approxi-mation of food item importance across a given year in theabsence of volume-based metrics (Leger and Didrichsons1994, Ciucci et al. 2014, Stenset et al. 2016).

To investigate whether a lack of natural foods in scatsinfluenced the odds of a scat containing anthropogenicfoods, we fit logistic regression models using maximumlikelihood via the glm function in R (Cherry et al. 2016,R Core Team 2016). We used binary (i.e., 1 or 0) oc-currences of food categories instead of FO because >1item within individual categories was present in mostscats and totals likely did not lack independence. Weused anthropogenic foods as the response variable, sea-son and natural foods categories as independent vari-ables, and one level of each variable as a reference. Weused Akaike’s Information Criterion corrected for smallsample size (AICc) for model selection (Burnham et al.2011), assigned significance to β estimates from the mostparsimonious model if P < 0.05, and converted β esti-mates to odds ratios. We assessed goodness-of-fit of ourtop model using a le Cessie–van Houwelingen–Copas–

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Fig. 2. Seasonal variation in frequency of occurrence (FO) of food item categories found in 166 Florida blackbear (Ursus americanus floridanus) scats collected during 2004–2006 in the Highlands–Glades subpopulationof south-central Florida, USA. Results of χ2-tests comparing FO of food item categories among seasons arealso presented. Categories were hard mast (Hard), soft mast (Soft), vegetation (Veg), invertebrates (Invert),vertebrates (Vert), and anthropogenic (Anthro).

Hosmer unweighted sum-of-squares test (Hosmer et al.1997) via the R package rms (Harrell 2017).

ResultsDuring 2004–2006, we collected 166 Florida black

bear scats, 27 (16.3%) of which were from 17 individ-ual bears that were live-captured during our study pe-riod. We recorded 532 occurrences of 50 different na-tive, non-native, and anthropogenic food items (Table1): winter–spring scats contained 96 occurrences of 28items, summer scats contained 151 occurrences of 35items, and autumn scats contained 285 occurrences of 42items. Seventeen (34.0%) of the 50 individual food itemswere present in scats from all 3 seasons.

We found significant FO differences among seasons forall natural foods categories but not anthropogenic foods(Fig. 2), and average annual FOs generally exhibited con-siderable variation (i.e., SD; Table 1). Among the majorfood categories, soft mast, invertebrates, and hard mastwere dominant across a year. Oak acorns had the highestaverage annual FO among specific food items, followedby anthropogenic corn and native Florida carpenter ants(Camponotus floridanus). Oak acorns, Florida carpen-ter ants, and saw palmetto fruit had the highest FOs inwinter–spring, summer, and autumn scats, respectively.

Feral hog (Sus scrofa), white-tailed deer (Odocoileus vir-ginianus), and gopher tortoise (Gopherus polyphemus)remains in summer scats resulted in the highest seasonalFO for vertebrates. Among anthropogenic foods, cornwas the most dominant across all seasons, followed bydeer chow during winter–spring and citrus fruit duringsummer and autumn; we documented few occurrencesof items indicative of garbage consumption (e.g., paperand plastic). The unweighted sum-of-squares test demon-strated adequate fit of the top regression model (SSE= 32.19; Z = 1.00; P = 0.31), which included bothsoft mast and vegetation as explanatory food categories(Table 2). Soft mast was the most important predictor ofanthropogenic food occurrence in scats; the odds of a scatcontaining anthropogenic foods significantly increased inthe absence of soft mast (Table 3).

DiscussionAcross the southeastern United States, oak acorns pro-

vide the calories and macronutrients (e.g., crude fat) in-tegral to black bear body fat accumulation during au-tumn hyperphagia (Pelton 2001), and our findings ex-tend this generalization to the HGS. Carbohydrate-richsaw palmetto also fruits during autumn and is consideredthe single most important natural food item throughout

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Table 1. Frequency of occurrence of food items in Florida black bear (Ursus americanus floridanus) scatscollected in the Highlands–Glades subpopulation of south-central Florida, USA, during the winter–spring (W),summer (S), and autumn (A) seasons of 2004–2006. Dashes (—) indicate the food item was not documentedduring that season, and # and n correspond to the total number of occurrences of each food item among allcollected scats and the scat sample size, respectively.

W S A Annual xFood item # n = 32 n = 39 n = 95 n = 166 SD

Hard mast 79 50.0 5.1 51.6 35.6 26.4Oak acorn (Quercus spp.) 63 50.0 2.6 47.4 33.3 26.6Hickory nut (Carya spp.) 16 — 2.6 11.6 4.7 6.1

Soft mast 126 18.7 71.8 67.4 52.6 29.5Saw palmetto (Serenoa repens) 61 3.1 10.2 56.8 23.4 29.2Unknown fruit 25 12.5 20.8 10.5 14.6 5.5Grape (Vitis spp.) 17 — 41.0 1.0 14.0 23.4Gallberry (Ilex glabra) 7 3.1 2.6 6.3 4.0 2.0Blueberry (Vaccinium spp.) 5 3.1 7.7 1.0 3.9 3.4Blackberry (Rubus spp.) 4 — 7.7 1.0 2.9 4.2Swamp tupelo (Nyssa biflora) 3 — — 3.2 1.1 1.8Cabbage palm (Sabal palmetto) 2 — — 3.2 1.1 1.8Dahoon holly (Ilex cassine) 1 3.1 — — 1.0 1.8Brazilian pepper (Schinus terebinthifolius)a 1 — — 2.1 0.7 1.2

Vegetation 51 46.9 41.0 15.8 34.6 16.5Leafy green vegetation 11 31.2 2.6 — 11.3 17.3Vegetation (general) 12 9.4 15.4 5.3 10.0 5.1Plant fiber 10 9.4 7.7 5.3 7.5 2.1Grass 11 — 12.8 6.3 6.4 6.4Palm heart (Sabal palmetto or Serenoa repens) 3 3.1 2.6 1.0 2.2 1.1Ragweed (Ambrosia spp.) 2 — — 3.2 1.1 1.8Smartweed (Polygonum spp.) 1 3.1 — — 1.0 1.8Lichen 1 — — 1.0 0.3 0.6

Invertebrate (Arthropoda) 163 40.6 66.7 48.4 51.9 13.4Hymenoptera 79 12.5 61.5 28.4 34.1 25.0

Florida carpenter ant (Camponotus floridanus) 49 12.5 48.7 26.3 29.2 18.3Acrobat ant (Crematogaster spp.) 7 3.1 15.4 — 6.2 8.1Bumble bee (Bombus spp.) 5 — 12.8 — 4.3 7.4Unknown bee 5 3.1 7.7 1.0 3.9 3.4Unknown ant 11 — 2.6 2.1 1.6 1.4Yellow jacket (Vespula spp.) 1 — 2.6 — 0.9 1.5Guinea wasp (Polistes exclamans) 1 — 2.6 — 0.9 1.5

Coleoptera 43 25.0 12.8 25.3 21.0 7.1Unknown beetle 17 28.1 10.2 17.9 18.7 9.0Weevil (Curculio spp.) 15 15.6 — 10.5 8.7 7.9Scarab beetle (Scarabaeidae) 2 6.2 7.7 6.3 6.7 0.8Bess bug (Odontotaenius disjunctus) 9 6.2 5.1 — 3.8 3.3

Unknown arthropod 20 9.4 20.5 12.6 14.2 5.7Isoptera 13 3.1 12.8 7.4 7.8 4.9

Subterranean termite (Rhinotermitidae) 8 3.1 5.1 5.3 4.5 1.2Unknown termite 5 — 7.7 2.1 3.3 4.0

Metastigmata 5 — 2.6 3.2 1.9 1.7Tick (Ixodidae) 5 — 2.6 3.2 1.9 1.7

Odonata 1 3.1 — — 1.0 1.8Dragonfly (Anisoptera) 1 3.1 — — 1.0 1.8

Diptera 1 — — 1.0 0.3 0.6Unknown fly 1 — — 1.0 0.3 0.6

Vertebrate 30 6.2 23.1 15.8 15.0 8.5Mammalia 21 6.2 20.5 11.6 12.8 7.2

Feral hog (Sus scrofa)a 4 — 7.7 1.0 2.9 4.2White-tailed deer (Odocoileus virginianus) 3 — 7.7 — 2.6 4.4Unknown hair or tissue 4 3.1 — 3.2 2.1 1.8Nine-banded armadillo (Dasypus novemcinctus)a 4 — 2.6 3.2 1.9 1.7Raccoon (Procyon lotor) 6 3.1 — 2.1 1.7 1.6

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Table 1. Continued.

W S A Annual xFood item # n = 32 n = 39 n = 95 n = 166 SD

Reptilia 4 — 2.6 3.2 1.9 1.7Gopher tortoise (Gopherus polyphemus) 4 — 2.6 3.2 1.9 1.7

Aves 5 — — 1.0 0.3 0.6Unknown feathers 5 — — 1.0 0.3 0.6

Anthropogenic 75 40.6 35.9 23.2 33.2 9.0Corn 41 40.6 28.2 18.9 29.2 10.9Deer chow 13 31.2 7.7 1.0 13.3 15.9Unknown grain 7 15.6 — 3.2 6.3 8.2Citrus 12 — 10.2 7.4 5.9 5.3Paper or plastic 2 3.1 — 1.0 1.4 1.6

Unknown food item 8 9.4 2.6 3.2 5.1 3.8

aNon-native natural food.

Florida black bear range (Maehr et al. 2001; Table 4).Collectively, energy-rich oak acorns and saw palmettofruit dominated autumn scats in the HGS (∼18,000–

Table 2. Logistic-regression model selection inves-tigating whether a lack of seasonal occurrences ofnatural food categories in Florida black bear (Ursusamericanus floridanus) scats influenced the oddsof a scat containing anthropogenic foods for theHighlands–Glades subpopulation in south-centralFlorida, USA (2004–2006). We used anthropogenicfoods as the response variable, and season and oc-currence of soft mast (Soft), hard mast (Hard), inver-tebrates (Invert), vertebrates (Vert), and vegetation(Veg) as explanatory variables. We used occurrenceof each natural foods variable as the reference levelto evaluate non-occurrence. For brevity, only models≤2 �AICc are presented.

Model AICca �AICc

b wic logLikd

∼ Soft + Veg 194.90 0.00 0.10 −94.36∼ Soft + Season 195.43 0.48 0.07 −93.55∼ Soft + Veg +

Hard195.61 0.68 0.06 −93.65

∼ Soft + Veg +Season

195.68 0.69 0.06 −92.59

∼ Soft + Veg +Invert + Season

196.00 1.12 0.05 −91.72

∼ Soft + Invert +Veg

196.12 1.26 0.05 −93.94

∼ Soft + Hard 196.60 1.68 0.04 −95.20∼ Soft + Invert +

Season196.65 1.71 0.04 −93.10

∼ Soft + Veg +Vert

196.69 1.74 0.04 −94.18

∼ Soft 196.83 1.93 0.03 −96.37

aAkaike’s Information Criterion corrected for small sample size.bDifference between AICc of model and model with the lowestAICc.cModel wt.dLog likelihood.

23,000 joules/gm dry mass; Abrahamson and Abraham-son 1989). Although autumn mast failures can have neg-ative demographic consequences on bear populations(Rogers 1976), Florida black bears can overcome suchfailures via a compensatory reliance on oak acorns andsaw palmetto fruit (Stratman and Pelton 1999). As a re-sult, productivities of those masting species likely act asprimary predictors of HGS reproductive rates and popu-lation growth (Rogers 1976, Maehr et al. 2001, Obbardand Howe 2008). Considering the severe habitat loss thatis expected to occur in the Lake Wales Ridge ecosystem(Carr and Zwick 2016), protection of remaining scrubcommunities that harbor both saw palmetto and most oakspecies (Weekley et al. 2008) may be critical to long-termpersistence of the HGS.

Winter-active male and non-parturient female blackbears are common in the milder climate of the South-eastern Coastal Plain where natural foods are available

Table 3. Model-averaged coefficient estimates (β)from the top logistic-regression model predictingoccurrence of anthropogenic food items in Floridablack bear (Ursus americanus floridanus) scats col-lected in the Highlands–Glades subpopulation ofsouth-central Florida, USA (2004–2006). Occurrenceof each natural foods variable was used as a refer-ence; thus, non-occurrence of those variables wasestimated. Standard errors (SE), odds ratios (eβ)and their 95% confidence intervals, z-values, andthe probabilities that β differed from 0 are alsopresented.

Variable β SE eβ 95% CI Z Pr (>|Z|)

Intercept −0.69 0.34 0.50 0.26–0.97 −2.05 0.04a

Soft mast 0.88 0.35 2.42 1.20–4.86 2.49 0.01a

Vegetation −0.76 0.38 0.47 0.22–0.98 −2.01 0.08

aα < 0.05.

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Table 4. Dominant food items in the annual diets of all 7 Florida black bear (Ursus americanus floridanus)subpopulations (Florida, USA), with foods listed in decreasing order of frequency of occurrence (FO). Samplesizes for each study area (n) and total number of unique food items found (#) are presented, as are FO valuesin parentheses. Modified from Maehr et al. (2001).

Subpopulation n # Food 1 Food 2 Food 3

Eglina 259 30 Beetles (46%) Oak acorns (38%) Saw palmetto fruit (17%)Apalachicolab,c 54 9 Swamp tupelo fruit (47.6%) Bayberry fruit (21.2%) Oak acorns (7.6%)Osceolad 703 27 Corn (29%) Saw palmetto fruit (17%) Blackgum fruit (11%)Ocala–St. Johnse 676 36 Oak acorns (59.6%) Saw palmetto fiber (27.4%) Sabal palmetto fruit (20.3%)Chassahowitzkaf 212 20 Vegetation (76%) Sabal palmetto fruit (70%) Saw palmetto fruit (37%)Highlands–Gladesg 166 50 Oak acorns (33.3%) Corn (29.2%) Florida carpenter ant (29.2%)Big Cypressh 739 44 Sabal palmetto fruit (29.4%) Saw palmetto fruit (22.7%) Brazilian pepper (22.1%)

aStratman and Pelton (1999).bMaehr and Brady (1984).cBased on analysis of stomach contents, not scats.dDobey et al. (2005).eRoof (1997).fOrlando (2003).gThis study.hMaehr (1997).

year-round (Hightower et al. 2002, Garrison et al. 2007),and radiomonitoring data confirmed some HGS bearswere winter-active during our study (Ulrey 2008, Guthrie2012). Although oak acorns dominated winter–springHGS scats, which exemplifies acorn overwintering, mastsurveys conducted in the study area indicated acornyields during our years of sampling were 54.8% higherthan the 27-year average (1988–2014; Bowman 2015).Scrub communities contain 5 of the 7 oak species of theLake Wales Ridge ecosystem and adjacent areas withinHGS primary range (Abrahamson and Layne 2003), butsubstantial scrub has already been lost (Weekley et al.2008). The magnitude of acorn overwintering that oc-curred is likely uncommon, and we therefore believe ourannual acorn FO is an overestimate. Our short 2-yearsampling period precluded an identification of the foodsthat winter-active Florida black bears may rely on duringyears of average or poor oak productivity, but winter–spring FOs suggest vegetation, anthropogenic foods, andinvertebrates may be important.

Most green vegetation (e.g., leaves, grasses, forbs,etc.) generally is considered of tertiary diet importanceto black bears in the southeastern United States becausethose items provide little nutritional value compared withother natural foods (Maehr et al. 2001, Inman and Pel-ton 2002). In contrast, anthropogenic foods are calorie-rich, typically require little energy expenditure to access,and are often exploited by bears when natural foods arescarce (Baruch-Mordo et al. 2014, Ditmer et al. 2016).Many hunters in the HGS area dispensed deer chow (anutrient-rich feed) and corn year-round at feeding stations

intended to supplement white-tailed deer diets, which ex-plains the presence of both of those anthropogenic foodsin scats across all seasons. Hightower et al. (2002) positedthat hunter-dispensed corn allowed some Louisiana blackbears (U. a. luteolus) to remain winter-active while main-taining a positive energy balance, and corn positivelyinfluenced vital rates of the Osceola black bear subpop-ulation in northern Florida (Dobey et al. 2005). Thus,hunter-dispensed corn at feeding stations has the poten-tial to sustain at least some winter-active bears, whichcould increase skeletal–lean body mass and improve in-dividual fitness (Robbins et al. 2004, Steyaert et al. 2014).

Bears can quickly habituate to corn and other anthro-pogenic foods, leading to increased human–bear conflictsthat could endanger humans and cause financial losses(Baruch-Mordo et al. 2014, Ditmer et al. 2016, Pente-riani et al. 2016). Florida black bears visiting feedingstations and depredating or damaging agricultural cropscollectively account for a prominent human–bear conflictcomplaint in the area occupied by the HGS (FWC 2012).Citrus fruit is the most widespread agricultural crop inthe Lake Wales Ridge ecosystem, groves of which wereimportant predictors of female bear road-crossings in theHGS (Guthrie 2012). Despite the close proximity of nu-merous groves to established bear subpopulations, ourstudy is the first to document citrus fruit in the diet ofFlorida black bears (Maehr et al. 2001). Although notseasonally or annually important, the limited macronutri-ents provided by citrus fruit (<1 g fat; <1 g protein; ≤12g carbohydrates) are insufficient for supporting mainte-nance or growth of lean body mass in bears. Therefore,

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the presence of citrus in summer scats anecdotally sug-gests higher quality natural foods were either limited inavailability or inaccessible during summer (Costello et al.2016).

Blueberry and blackberry fruits that other Florida blackbear subpopulations relied on during summer (Maehrand DeFazio 1985, Maehr et al. 2001) had nominal FO,whereas lower nutrition grapes (Vitis spp.) had the high-est FO among soft mast in summer scats. Interspecificcompetition for quality summer soft mast is extraordinaryamong vertebrates and could rapidly erode fruit availabil-ity despite high productivity (Inman and Pelton 2002).Heightened occurrence of vertebrate remains in summerscats further supports limited soft mast availability duringour sampling. Those remains included white-tailed deer,indicating predation of neonates rather than kleptopara-sitism of hunter kills or scavenging (Zager and Beecham2006); and predation of neonate ungulates by black bearshas been posited as a response to shortages of naturalvegetal foods (Belant et al. 2006, Svoboda et al. 2011).

Other studies noted the impacts that soft mast short-ages can have on black bear populations, such as de-pressed vital rates, and the relationship of shortages withhuman–bear conflicts (Inman and Pelton 2002, Obbardand Howe 2008, Romain et al. 2013). We found height-ened dietary reliance on anthropogenic food sources assoft mast occurrence declined, a response that wouldincrease human–bear conflicts assuming anthropogenicfoods are a reliable proxy (Howe et al. 2010, Hopkinset al. 2014). Our FO estimates indicate corn is the mostlikely substitute for soft mast among anthropogenic fooditems, but human–bear conflicts at feeding stations lo-cated in rural areas may be less severe relative to thoseassociated with other human-sourced foods (Merkle et al.2013, Ditmer et al. 2016). Despite not collecting scats inthe urbanized north-central part of HGS primary rangewhere human population density is highest, we docu-mented a few occurrences of garbage in scats. Bearsfrequenting urban areas to access garbage can result inconditioning to human presence, loss of fear of humans,and injurious aggression toward humans (Elfstrom et al.2014, Penteriani et al. 2016). Citrus fruit is Florida’s topcash crop (∼US$1.10 billion income annually; Gitzen2015); therefore, contentious and costly conflicts withhumans could also develop if HGS bears increase citrusfruit consumption or cause damage to citrus trees.

Whether or not the anthropogenic foods available toHGS bears can support a sufficient portion of the popula-tion necessary to ensure long-term persistence in the faceof imminent habitat loss is unclear. Although nutrient-poor citrus fruit is incapable of doing so, carbohydrate-

rich corn and deer chow are easily accessible and hunter-dispensed corn provided approximately 8,000% of theamount of hard and soft mast available to bears in Vir-ginia, USA, during years of mast failures (Gray et al.2004). Anthropogenic foods were, however, not amongthe most dominant summer-food categories in HGS scats.Invertebrates were the only category with consistentlymoderate to high FO across all seasons, a finding that waslargely influenced by myrmecophagy of Florida carpen-ter ants during summer. Ants are a protein- and lipid-richfood that can support lean mass accumulation in bearsif consumed in large, concentrated amounts, such as atformicaries (Lopez-Alfaro et al. 2013). Studies of blackand brown bear (U. arctos) populations elsewhere notedthe importance of ants and other invertebrates in beardiets, which can offset the metabolic consequences ofmast shortages and reduce consumption of anthropogenicfoods (Auger et al. 2006, Coogan et al. 2014, Stenset et al.2016). Although no other Florida black bear subpopu-lation exhibited appreciable myrmecophagy, our resultsindicate that bears in the HGS primarily compensatedfor summer soft mast shortages by consuming Floridacarpenter ants and other invertebrates, which are likelyreliable food sources with minimal abundance fluctua-tions. Florida carpenter ants and weevils, including thegiant palm weevil (Rhynchophorus cruentatus), are ar-boreal species that are acutely dependent on remainingbear habitat for proliferation (Tedder et al. 2012). Thus,impending habitat loss could also reduce populations ofthose important invertebrates and increase consumptionof anthropogenic foods by HGS bears.

Much of the uncertainty in our results is a function ofsampling duration, which was too short to account forsuper-annual mast fluctuations (Craighead et al. 1995),and small seasonal sample sizes of scats. Pooling within-season scats across years to overcome the latter issueresulted in sample sizes that were skewed toward autumnwhen bear food consumption and defecation rates aretypically highest (Dahle et al. 1998, Ciucci et al. 2014),thereby attributing more weight to food items in autumnscats (i.e., pooling fallacy; Machlis et al. 1985, Legerand Didrichsons 1994). Therefore, FO probably overes-timated the importance of smaller sized oak acorns whileunderestimating the importance of larger sized foods,such as vertebrates (Klare et al. 2011). Locations of oursample collections were also clustered in 3 areas of highFlorida black bear use (Ulrey 2008, Guthrie 2012), whichlikely exacerbated said issue by violating the assump-tion of sample independence (Klare et al. 2011). Further-more, because some natural foods are endemic to remnanthabitat communities (e.g., scrub palmetto fruit) that are

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difficult to access without substantial risk to bears (e.g.,crossing roads) as a result of habitat loss and fragmen-tation (Guthrie 2012), our clustered sampling may nothave detected all of the foods consumed by bears. Al-though increasing our winter–spring and summer scatsample sizes would have been difficult because of thesmall number of bears in the HGS, future dietary studiesshould conduct sampling over a longer temporal period(e.g., >3 consecutive yr) to account for mast fluctuations(Romain et al. 2013). Estimating volume-based metricsin our study would have been unlikely to facilitate moreinsightful comparisons among Florida bear subpopula-tions, but should be used in conjunction with FO forfuture studies to better approximate dietary importanceof specific food items (Klare et al. 2011, Ciucci et al.2014, Stenset et al. 2016).

Management implicationsFederally endangered scrub communities contain nu-

merous high-quality hard and soft mast–producing flora(e.g., saw palmetto, blueberry, and 5 species of oak;Abrahamson et al. 1984, Layne and Abrahamson 2010);therefore, we suggest managers consider intensifying ef-forts to protect remnant patches of scrub via state andfederal agency acquisition or conservation easements tothwart further loss. Soft mast generally appears to bethe most important food category to Florida black bearsin the HGS, and the lack thereof is associated with in-creased consumption of anthropogenic foods; therefore,habitat conservation should also include other commu-nities with quality soft-masting shrubs and plants, suchas flatwoods and sandhills (Abrahamson and Abraham-son 1989, Layne and Abrahamson 2010). An indirectbyproduct of those habitat conservation efforts is main-tenance of arboreal Florida carpenter ant populations forbears to consume during years of poor mast yields orin the event that masting flora abundance and distribu-tion is reduced by anthropogenic development. Althoughhunter-dispensed corn at wildlife feeders provides a nu-tritious, easily accessible supplemental food for bears,such feeding could result in habituation and lead to bearsincreasing exploitation of other anthropogenic foods thatare in closer proximity to humans (e.g., garbage) or areagricultural commodities (e.g., citrus fruit). Small size ofthe HGS should limit human–bear conflict managementto primarily non-lethal methods, so we suggest managersincrease public education and outreach (Pienaar et al.2015) and expand agency-assistive anthropogenic-food–management programs to the HGS area (Barrett et al.2014). Finally, our samples were collected a decade prior

to present; therefore, we strongly suggest repeating ourstudy over a longer duration to investigate whether di-etary shifts occur in response to impending habitat lossand to further inform habitat and subpopulation conser-vation and human–bear conflict management.

AcknowledgmentsWithout support from multiple private landowners,

particularly the Smoak, Hendrie, and Lightsey families,this study would not have been possible. We are gratefulfor the support from J. N. Layne, C. R. Abrahamson, H.M. Swain, and the late L. D. Harris and late L. V. Layne.We thank the numerous staff at Archbold Biological Sta-tion who provided assistance—including E. S. Mengesand M. A. Deyrup—and the Florida Fish and WildlifeConservation Commission for supporting our efforts. Weespecially thank R. Bowman for providing access to hislong-term data set of oak productivity in the Lake WalesRidge ecosystem. We appreciate the useful commentsand constructive criticism provided by reviews from P.Ciucci, J. L. Belant, B. K. Scheick, and 2 anonymousreviewers, all of which improved this manuscript. Wealso thank T. E. Boal for copyediting this manuscript.This study was funded by the Disney Worldwide Con-servation Fund; supplementary funds were provided byArchbold Biological Station. We dedicate this paper to D.S. Maehr and M. G. Smoak, both of whom tragically per-ished while conducting aerial radiotelemetry monitoringof black bears in the HGS. Any opinions, findings, con-clusions, or recommendations expressed herein are thoseof the authors and do not necessarily reflect the viewsof the University of Kentucky. Use of trade, product, orfirm names is for descriptive purposes only and does notimply endorsement by the University of Kentucky.

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Received: October 22, 2016Accepted: March 29, 2017Associate Editor: Ciucci

Ursus 28(1):92–104 (2017)


Documents

Food habits of a small Florida black bear population in an