Figures
Abstract
Populations of mesopredators (mid-sized mammalian carnivores) are expanding in size and range amid declining apex predator populations and ever-growing human presence, leading to significant ecological impacts. Despite their obvious importance, population dynamics have scarcely been studied for most mesopredator species. Information on basic population parameters and processes under a range of conditions is necessary for managing these species. Here we investigate survival, recruitment, and population growth rate of a widely distributed and abundant mesopredator, the northern raccoon (Procyon lotor), using Pradel’s temporal symmetry models and >6 years of monthly capture-mark-recapture data collected in a protected area. Monthly apparent survival probability was higher for females (0.949, 95% CI = 0.936–0.960) than for males (0.908, 95% CI = 0.893–0.920), while monthly recruitment rate was higher for males (0.091, 95% CI = 0.078–0.106) than for females (0.054, 95% CI = 0.042–0.067). Finally, monthly realized population growth rate was 1.000 (95% CI = 0.996–1.004), indicating that our study population has reached a stable equilibrium in this relatively undisturbed habitat. There was little evidence for substantial temporal variation in population growth rate or its components. Our study is one of the first to quantify survival, recruitment, and realized population growth rate of raccoons using long-term data and rigorous statistical models.
Citation: Troyer EM, Cameron Devitt SE, Sunquist ME, Goswami VR, Oli MK (2014) Survival, Recruitment, and Population Growth Rate of an Important Mesopredator: The Northern Raccoon. PLoS ONE 9(6): e98535. https://doi.org/10.1371/journal.pone.0098535
Editor: Gabriele Sorci, CNRS, Université de Bourgogne, France
Received: November 1, 2013; Accepted: May 5, 2014; Published: June 5, 2014
Copyright: © 2014 Troyer et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Funding: This study was supported by the Ordway-Swisher Biological Station, the School of Natural Resources and Environment, and the Department of Wildlife Ecology and Conservation, University of Florida. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Competing interests: The authors have declared that no competing interests exist.
Introduction
Mesopredators, or predators at middle levels of food webs, are important contributors to ecosystem function and have significant impacts on a wide range of species [1]. They can exert their influence through many means, including predation [2], competition with specialist species [3], and the spread of pathogens [4]. These effects are often heightened by the resilience and rapid growth of mesopredator populations, particularly in the presence of human settlements [5]. Basic information on mesopredator population ecology and dynamics, though crucial for developing effective conservation and management strategies, is lacking for many of these species.
One particularly abundant and widely distributed mesopredator species in the United States is the northern raccoon, Procyon lotor. The raccoon has proven highly successful in the past century with dramatic increases in both abundance and distribution, probably due to its skill in exploiting anthropogenic resources as well as the decimation of North American large carnivore populations [6]. In addition, the raccoon has been introduced to Japan [7], to the former Soviet Union [8], to the Queen Charlotte Islands in Canada [9], and across mainland Europe [10]. Population control efforts in these areas are hampered by insufficient knowledge of raccoon population ecology outside their native range.
As an abundant mesopredator, the raccoon has significant impacts on other species. Predation by raccoons has been shown to suppress the reproductive success of songbirds [11], waterfowl [12], and sea turtles [13], and to regulate some populations of the white-footed mouse, Peromyscus leucopus, [14] and the endangered Key Largo woodrat, Neotoma floridana smalli [15]. The raccoon also serves as a reservoir and vector for many diseases and parasites, including rabies, canine distemper, and raccoon roundworm [16]. Some of these diseases can harm less-resilient populations of other species, such as the critically endangered island fox, Urocyon littoralis, [17], and others can infect livestock and interfere with farming operations [18]. Because they tend to thrive in the presence of human settlements, raccoons often become nuisance animals and can even pose a threat to humans as carriers of rabies and roundworms [19], [20].
Clearly, raccoons have substantial impacts on ecology, economics, and public health, and their population dynamics are central to these impacts. However, our knowledge of their population ecology is incomplete. While raccoon survival has been estimated in many systems [21]–[24], recruitment and population growth rate have rarely or never been assessed despite being key parameters in raccoon population dynamics.
Our goal was to investigate demographic parameters and population dynamics of raccoons in a relatively undisturbed area using a detailed, long-term dataset and state-of-the-art modeling techniques. We estimated and modeled apparent survival, recruitment, and realized finite population growth rate (hereafter, population growth rate or growth rate) and tested the following hypotheses regarding these parameters: (1) Males would have lower apparent survival and higher recruitment than females, because males are more likely to disperse away from their natal population and join other populations [6]. (2) Population growth rate would covary more strongly with survival than with recruitment. Raccoons usually survive long enough to experience several breeding opportunities per lifetime, and population growth rates of species with this life history characteristic tend to be more strongly influenced by survival than reproductive rates [25]–[27].
Materials and Methods
Ethics Statement
All field methods followed guidelines of the American Society of Mammalogists [28] and were approved by the Animal Care and Use Committee at the University of Florida (approval number A023).
Study Area and Species
We carried out fieldwork at the Ordway-Swisher Biological Station (OSBS), a field station located in north-central Florida (about 29.7°N and 82.0°W). OSBS is managed by the University of Florida and comprises more than 3,750 ha of protected habitat that is maintained in a fairly natural, undisturbed state. The station has a mosaic of dry and wet habitat types, including sandhills, xeric hammock, upland mixed forest, swamps, marshes, and lakes, as well as a riverine system connecting to the St. John’s River. Precipitation and temperature in the region vary seasonally–about 60 percent of annual rainfall occurs between May and September, and the temperature occasionally falls below freezing between December and March. Primary productivity, which is correlated with rainfall, is also seasonal [29]. The size of the study area remained constant throughout the period of data collection. Because the land at OSBS is protected, there was no harvesting of wildlife.
The northern raccoon is a common medium-sized carnivore across much of the United States. Some aspects of the life history and ecology of raccoons have been fairly well studied, particularly in the Midwest. In most parts of their range, the mating season lasts from January through March, peaking in February [6]. Pregnancies last around two months, resulting in a birth peak in April [6]. In the Southeast, mating generally begins later and lasts longer [6]. For example, raccoons in the mangrove swamps of southern Florida mate from March through August and give birth between May and October, with no well-defined breeding season [30]. Although no formal study has been done on breeding phenology of raccoons in north-central Florida, raccoons in this area appear to be capable of breeding year-round (M. Sunquist, pers. obs.). Litter sizes vary positively with latitude and female body size [31], commonly averaging between 3 and 4 young [32]–[34].
Females are sexually mature in the first breeding season after their birth, although yearlings usually have much lower pregnancy rates than adults [6]. If a female does not become pregnant in the regular breeding season or loses her litter soon after birth, she can experience a second estrus and produce a litter later in the year, but one litter per female per year seems to be the limit [6]. Most adult raccoons survive to breed for more than one season, but few live beyond five years [35].
Field Methods
Raccoons were trapped once per month from September 1992 to December 1998 (76 occasions) as part of a capture-mark-recapture field study on mesopredators at OSBS. A total of 25 Tomahawk live traps were set at approximately 0.4-km intervals along a major flow-through drainage on the station. Traps were active for four consecutive nights in March and May and for two consecutive nights in all other months; we treated these multi-day trapping periods as single capture occasions in our analyses. Captured individuals were immobilized with Ketaset at a dose of 10 mg per kg of estimated body weight. They were then marked, weighed, measured, sexed, and released at the capture location. Raccoons were initially radio-tagged with a small tag in each ear. Starting in the second year of the study, due to a few instances of tag loss, raccoons were instead marked with a microchip that was inserted just under the skin on the back of the neck.
Capture-Mark-Recapture Analyses
We used two parameterizations of Pradel’s [36] temporal symmetry model to estimate and model survival, recruitment, and population growth rate. One (φ and λ parameterization) estimates apparent survival probability (φ), recapture probability (p), and realized population growth rate (λ); the other (φ and f parameterization) estimates recruitment (f) rate instead of population growth rate. We carried out all analyses using program MARK [37] version 6.2 implemented through the RMark package for program R [38] version 2.15.2. For model selection, we used an information-theoretic approach with Akaike’s information criterion corrected for small sample size (AICc) to determine model parsimony and make statistical inferences [39], [40]. We treated all raccoons within the study area as part of one open population.
Pradel’s model is sensitive to trap response, or differences in capture probabilities of marked vs. unmarked individuals [41]. Several raccoons in this study appeared to be “trap happy” and repeatedly reentered traps to retrieve bait (M. Sunquist, pers. obs.). To reduce bias caused by trap response, we removed all individuals that were caught on 5 or more consecutive occasions from the data.
We ran two model sets to determine the best model structure for each parameter: one using the φ and λ parameterization and one using the φ and f parameterization. In each set, we tested for the effects of sex, month, season, and additive and interactive effects between sex and the other variables on each parameter (recapture probability, apparent survival, recruitment rate, and population growth rate). We parameterized our models in RMark using fully time-dependent parameter index matrices (PIMs); models were constrained using the design matrix. Because data were collected in monthly intervals and all models were parameterized using time-dependent PIMs, all estimates of model parameters were monthly, regardless of the model structure. We considered four biologically relevant seasons based on preliminary analyses and climatic patterns of the region: March–May (spring), June–August (summer), September–November (fall), and December–February (winter).
We tested goodness of fit using RELEASE TEST 2+3. We found no evidence for lack of fit or overdispersion (χ2346 = 252.58, P = 1.00, ĉ = 0.73).
Results
There were 1,095 captures of 348 raccoons over the course of the field study. Of these individuals, 7 were captured on 5 or more consecutive occasions and were therefore excluded from analyses. The final dataset included 983 captures of 341 raccoons, with 343 captures of 112 females and 640 captures of 229 males. The average number of captures per individual was close to 3 for both sexes, but overall there were twice as many males in the study as females.
Recapture Probability
The best model for recapture probability, with a cumulative weight of 0.809 in the recruitment model set and 0.897 in the lambda model set, included an additive effect of month and sex (Table 1). Monthly recapture probabilities based on this model were consistently higher for males than females (Figure 1); estimates from model {φ(sex)p(month+sex)λ(season)} were highest in March (0.323, 95% CI = 0.267–0.384 for males; 0.241, 95% CI = 0.193–0.296 for females) and lowest in November (0.130, 95% CI = 0.100–0.168 for males; 0.091, 95% CI = 0.068–0.120 for females). The peaks in recapture probability during March and May probably result from the longer capture period in those months (4 nights of trapping compared with 2 nights for all other months; see Methods).
Estimates and 95% confidence intervals are from model {φ(sex)p(month+sex)λ(season)}.
Apparent Survival Probability
All well-supported models (ΔAICc <14 under both parameterizations, Table 1) included an effect of sex on survival probability, providing strong evidence that monthly survival differed between sexes. The top model for survival, with a cumulative weight of 0.857 in the recruitment model set and 0.737 in the lambda model set, included no temporal variation in survival. Estimates of monthly survival from model {φ(sex)p(month+sex)λ(season)} were 0.949 for females (95% CI = 0.936–0.960) and 0.908 for males (95% CI = 0.893–0.920). Annual survival based on these monthly values was 0.534 for females (95% CI = 0.452–0.610) and 0.313 for males (95% CI = 0.258–0.370).
The second-best model for survival, with a cumulative weight of 0.110 in the recruitment model set and 0.247 in the lambda model set, included an additive effect of season and sex. Estimates of monthly survival from model {φ(season+sex)p(month+sex)λ(season)} are shown in Figure 2A. However, the 95% confidence intervals of these estimates overlapped for all seasons, and the 95% confidence intervals for the β parameters of all seasons included zero, indicating little evidence for seasonal variation in survival.
Estimates and 95% confidence intervals are from the top-ranked model that included season for each parameter: {φ(season+sex)p(month+sex)λ(season)} for survival, {φ(sex)p(month+sex)f(season+sex)} for recruitment, and {φ(sex)p(month+sex)λ(season)} for population growth rate.
Recruitment Rate
Monthly recruitment rate differed between sexes (ΔAICc<12, Table 1A). The best-supported model, which had a cumulative weight of 0.629, included an additive effect of sex and season. Estimates of monthly recruitment from model {φ(sex)p(month+sex)f(season+sex)} were consistently higher for males than for females (Figure 2B), peaking in summer (0.125 for males, 95% CI = 0.069–0.217; 0.074 for females, 95% CI = 0.040–0.133).
Although {φ(sex)p(month+sex)f(season+sex)} was the top model, the 95% confidence intervals for the β parameters of all seasons included zero, and the 95% confidence intervals for the recruitment estimates from this model overlapped between all seasons. These confidence intervals suggested little or no evidence for discernible seasonal variation in recruitment rate. The second-best model for recruitment (cumulative weight = 0.292) included an effect of sex with no temporal variation, further suggesting that recruitment rate did not vary substantially over time. Monthly recruitment estimates from model {φ(sex)p(month+sex)f(sex)} were 0.091 for males (95% CI = 0.078–0.106) and 0.054 for females (95% CI = 0.042–0.067).
Realized Population Growth Rate
The best-supported model for population growth rate included an effect of season and had a cumulative weight of 0.554 (Table 1B). Estimates of monthly growth rate from model {φ(sex)p(month+sex)λ(season)} are shown in Figure 2C; the highest estimate was 1.031 (95% CI = 0.985–1.079), which occurred in spring. Model {φ(sex)p(month+sex)λ(season+sex)} had a ΔAICc<2 and a cumulative weight of 0.286 (Table 1B), suggesting a sex difference in population growth rate in addition to seasonal variation. However, in both these top models, the 95% confidence intervals of all β parameters for season and sex included zero. These confidence intervals indicate little evidence that population growth rate varied seasonally or between sexes.
Consistent with this lack of compelling evidence for any variation in population growth rate, the third-best supported model for growth rate was the constant parameter model. This model, {φ(sex)p(month+sex)λ(.)}, estimated a monthly population growth rate of 1.000 (95% CI = 0.996–1.004). The annual population growth rate derived from this estimate was 0.997 (95% CI = 0.948–1.050). A realized population growth rate of 1 means that the population size is neither increasing nor decreasing, indicating that our study population may have reached a stable equilibrium.
Based on the confidence intervals of effect sizes and real estimates, as described in the preceding sections, there was little evidence that population growth rate or its components (survival and recruitment) varied substantially over time. We show seasonal estimates of these parameters in Figure 2 to give an idea of what the temporal dynamics might be, but differences in parameter estimates between seasons are slight.
Discussion
Mesopredators constitute one of the most ecologically influential groups of vertebrates in the modern world, but research on their population ecology is remarkably scarce and limited in scope and often uses coarse-scale data [24], [42]. Our goal in this study was to report rigorous estimates of survival, recruitment, and population growth rate for a ubiquitous mesopredator, the northern raccoon, based on a long-term dataset. We found that raccoon population parameters in our relatively undisturbed system varied little over time, indicating a fairly stable population size.
Consistent with our hypothesis, male raccoons had lower apparent survival and higher recruitment, probably due to the permanent immigration and emigration of males to and from the study area associated with natal and breeding dispersal. The same pattern has been found for Virginia opossums (Didelphis virginiana) in this system, an ecologically similar mesopredator species that also exhibits male-biased natal and breeding dispersal [43]. In other mesopredator populations, sex differences in survival are often not present. Clearly, the conditions in each system and life history characteristics of each species (e.g., cost of reproduction, differential parental investment) influence whether one sex will have higher survival than the other, but most studies do not investigate what those factors are [21], [23], [42].
Precipitation and temperature determine primary productivity and thus also influence higher levels of food webs. Because rainfall and temperatures in our study site vary over time, we expected evidence of temporal variation in some or all of the population parameters we studied. Many other studies have found links between population dynamics and climatic variables [44]–[46]. However, we found little evidence that either population growth rate or its components varied substantially over time. Raccoons are highly adaptable in terms of diet and habitat tolerance, and the climate in Florida is relatively mild with a low range of variation. These factors likely minimized any temporal variation in raccoon population dynamics that might have resulted from climatic variation.
In contrast, a sympatric population of Virginia opossums showed monthly variation in population growth rate and recruitment, strong covariation between these parameters, and a positive association of these parameters with precipitation variability (coefficient of variation of rainfall) [43]. While opossums and raccoons are ecologically similar as mesopredators, they follow different life history strategies–opossums live a faster life, with rapid reproduction and early senescence; raccoons live a slower life, with smaller litters spaced over longer lifespans [27]. In addition, opossums have clearly-defined breeding seasons [29], while Florida raccoons can apparently breed year-round (M. Sunquist, pers. obs.). These different strategies appear to have resulted in distinct population dynamic patterns. In general, population size is less temporally variable in species with slower life histories than in those with faster life histories. The relative influence of vital rates on population growth rate also depends on life history strategy, in that population growth rate tends to be more sensitive to survival in slow species and to recruitment in fast species [25], [47]. This example further illustrates the importance of detailed studies on the population ecology of individual mesopredator species. Even though these species often have similar diets, habitat preferences, and levels of human tolerance, dissimilarities in their reproductive schedules can cause their populations to function differently.
Although some aspects of raccoon ecology have been studied intensively [33], [48]–[51], there has been little focus on raccoon population dynamics and the factors and processes underlying population growth rate. This study is the first to provide rigorous estimates of population growth rate and its underlying vital rates for raccoons in a natural habitat, and the results suggest that this undisturbed population was at a stable equilibrium. For many other mesopredator species, basic population ecology is poorly understood, which can hamper efforts to determine drivers of mesopredator population dynamics and factors that allow mesopredators to thrive in a variety of habitats. As human impacts continue to grow in magnitude around the world [52]–[54], human-tolerant mesopredators will continue to increase in distribution and impact as well, with potentially devastating consequences for biodiversity [1], [55]. Comparative studies of mesopredator population ecology in relatively undisturbed versus heavily disturbed habitats, including some quantification of mesopredator impacts on communities in each habitat type, would allow us to better understand how mesopredator populations respond to human disturbance and how these responses might affect community structure in general.
Acknowledgments
We thank the numerous volunteers who assisted in data collection. We are grateful to J. D. Nichols for providing much-needed guidance in data analysis and to G. Sorci, B. K. Sandercock and two anonymous reviewers for many thoughtful comments. Finally, we thank the late J. F. Eisenberg for his support and active involvement in trapping and data collection. He was always a stimulating partner on the trap line.
Author Contributions
Analyzed the data: EMT VRG MKO. Wrote the paper: EMT SECD MES VRG MKO. Designed the field study and collected data: MES.
References
- 1. Prugh LR, Stoner CJ, Epps CW, Bean WT, Ripple WJ, et al. (2009) The rise of the mesopredator. Bioscience 59: 779–791.
- 2. Crooks KR, Soule ME (1999) Mesopredator release and avifaunal extinctions in a fragmented system. Nature 400: 563–566.
- 3. DeVault TL, Olson ZH, Beasley JC, Rhodes OE Jr (2011) Mesopredators dominate competition for carrion in an agricultural landscape. Basic and Applied Ecology 12: 268–274.
- 4. Roemer GW, Gompper ME, Van Valkenburgh B (2009) The ecological role of the mammalian mesocarnivore. Bioscience 59: 165–173.
- 5. DeStefano S, DeGraaf RM (2003) Exploring the ecology of suburban wildlife. Frontiers in Ecology and the Environment 1: 95–101.
- 6.
Zeveloff SI (2002) Raccoons: a natural history. Washington, D.C.: Smithsonian Institution Press.
- 7. Asano M, Matoba Y, Ikeda T, Suzuki M, Asakawa M, et al. (2003) Reproductive characteristics of the feral raccoon (Procyon lotor) in Hokkaido, Japan. Journal of Veterinary Medical Science 65: 369–373.
- 8. Aliev FF, Sanderson GC (1966) Distribution and status of the raccoon in the Soviet Union. Journal of Wildlife Management 30: 497–502.
- 9. Hartman LH, Eastman DS (1999) Distribution of introduced raccoons Procyon lotor on the Queen Charlotte Islands: implications for burrow-nesting seabirds. Biological Conservation 88: 1–13.
- 10. Beltran-Beck B, Garcia FJ, Gortazar C (2012) Raccoons in Europe: disease hazards due to the establishment of an invasive species. European Journal of Wildlife Research 58: 5–15.
- 11. Schmidt KA (2003) Nest predation and population declines in Illinois songbirds: a case for mesopredator effects. Conservation Biology 17: 1141–1150.
- 12. Frey SN, Conover MR (2006) Habitat use by meso-predators in a corridor environment. Journal of Wildlife Management 70: 1111–1118.
- 13. Garmestani AS, Percival HF (2005) Raccoon removal reduces sea turtle nest depredation in the ten thousand islands of Florida. Southeastern Naturalist 4: 469–472.
- 14. Eagan TS, Beasley JC, Olson ZH, Rhodes OE Jr (2011) Impacts of generalist mesopredators on the demography of small-mammal populations in fragmented landscapes. Canadian Journal of Zoology 89: 724–731.
- 15. Winchester C, Castleberry SB, Mengak MT (2009) Evaluation of factors restricting distribution of the endangered Key Largo woodrat. Journal of Wildlife Management 73: 374–379.
- 16. Page LK, Swihart RK, Kazacos KR (1998) Raccoon latrine structure and its potential role in transmission of Baylisascaris procyonis to vertebrates. American Midland Naturalist 140: 180–185.
- 17. Timm SF, Munson L, Summers BA, Terio KA, Dubovi EJ, et al. (2009) A suspected canine distemper epidemic as the cause of a catastrophic decline in Santa Catalina Island foxes (Urocyon littoralis catalinae). Journal of Wildlife Diseases 45: 333–343.
- 18. Atwood TC, Deliberto TJ, Smith HJ, Stevenson JS, Vercauteren KC (2009) Spatial ecology of raccoons related to cattle and bovine tuberculosis in northeastern Michigan. Journal of Wildlife Management 73: 647–654.
- 19. McLean RG (1971) Rabies in raccoons in the southeastern United States. Journal of Infectious Diseases 123: 680–681.
- 20. Hernandez SM, Galbreath B, Riddle DF, Moore AP, Palamar MB, et al. (2013) Baylisascaris procyonis in raccoons (Procyon lotor) from North Carolina and current status of the parasite in the USA. Parasitology Research 112: 693–698.
- 21. Chamberlain MJ, Hodges KM, Leopold BD, Wilson TS (1999) Survival and cause-specific mortality of adult raccoons in central Mississippi. Journal of Wildlife Management 63: 880–888.
- 22. Gehrt SD, Fritzell EK (1999) Survivorship of a nonharvested raccoon population in South Texas. Journal of Wildlife Management 63: 889–894.
- 23. Hasbrouck JJ, Clark WR, Andrews RD (1992) Factors associated with raccoon mortality in Iowa. Journal of Wildlife Management 56: 693–699.
- 24. Urbanek RE, Nielsen CK, Wilson SE (2009) Survival of unexploited raccoons on a rural refuge in southern Illinois. Transactions of the Illinois State Academy of Science 102: 217–223.
- 25. Oli MK, Dobson FS (2003) The relative importance of life-history variables to population growth rate in mammals: Cole’s prediction revisited. American Naturalist 161: 422–440.
- 26. Oli MK, Dobson FS (2005) Generation time, elasticity patterns, and mammalian life histories: A reply to Gaillard, et al. American Naturalist 166: 124–128.
- 27. Promislow DEL, Harvey PH (1990) Living fast and dying young: a comparative analysis of life-history variation among mammals. Journal of Zoology 220: 417–437.
- 28. Sikes RS, Gannon WL, Mammalogists tACaUCotASo (2011) Guidelines of the American Society of Mammalogists for the use of wild mammals in research. Journal of Mammalogy 92: 235–253.
- 29. Sunquist ME, Eisenberg JF (1993) Reproductive strategies of female Didelphis. Bulletin of the Florida Museum of Natural History 36: 109–140.
- 30. Bigler WJ, Hoff GL, Johnson AS (1981) Population characteristics of Procyon lotor marinus in estuarine mangrove swamps of southern Florida. Florida Scientist 44: 151–157.
- 31. Ritke ME (1990) Quantitative assessment of variation in litter size of the raccoon Procyon lotor. American Midland Naturalist 123: 390–398.
- 32. Clark WR, Hasbrouck JJ, Kienzler JM, Glueck TF (1989) Vital statistics and harvest of an Iowa raccoon population. Journal of Wildlife Management 53: 982–990.
- 33. Fritzell EK, Hubert GF, Meyen BE, Sanderson GC (1985) Age-specific reproduction in Illinois and Missouri raccoons. Journal of Wildlife Management 49: 901–905.
- 34. Payne NF, Root DA (1986) Productivity of raccoons in southwestern Wisconsin, USA. Transactions of the Wisconsin Academy of Sciences Arts and Letters 74: 75–80.
- 35. Lotze JH, Anderson S (1979) Procyon lotor. Mammalian Species 119: 1–8.
- 36. Pradel R (1996) Utilization of capture-mark-recapture for the study of recruitment and population growth rate. Biometrics 52: 703–709.
- 37.
White GC, Burnham KP (1999) Program MARK: survival estimation from populations of marked animals. Bird Study 46 (supplement): S120–S139.
- 38.
Laake JL, Rexstad EA (2010) RMark. In: Cooch EG, White GC, editors. Program MARK: a gentle introduction. http://www.phidot.org/software/mark/docs/book/. C1–C108.
- 39.
Burnham KP, Anderson DR (2002) Model selection and multimodel inference: a practical information-theoretic approach. New York: Springer-Verlag.
- 40.
Williams BK, Nichols JD, Conroy MJ (2002) Analysis and management of animal populations. San Diego, CA: Academic Press.
- 41. Hines JE, Nichols JD (2002) Investigations of potential bias in the estimation of lambda using Pradel’s (1996) model for capture-recapture data. Journal of Applied Statistics 29: 573–587.
- 42. Kamler JF, Gipson PS (2004) Survival and cause-specific mortality among furbearers in a protected area. American Midland Naturalist 151: 27–36.
- 43. Troyer EM, Cameron Devitt SE, Sunquist ME, Goswami VG, Oli MK (2014) Density dependence or climatic variation? Factors influencing survival, recruitment, and population growth rate of Virginia opossums. Journal of Mammalogy 95: 421–430.
- 44. Campbell RD, Nouvellet P, Newman C, Macdonald DW, Rosell F (2012) The influence of mean climate trends and climate variance on beaver survival and recruitment dynamics. Global Change Biology 18: 2730–2742.
- 45. Galiano D, Kubiak BB, Marinho JR, Ochotorena de Freitas TR (2013) Population dynamics of Akodon montensis and Oligoryzomys nigripes in an Araucaria forest of Southern Brazil. Mammalia 77: 173–179.
- 46. Fordham DA, Sinclair RG, Peacock DE, Mutze GJ, Kovaliski J, et al. (2012) European rabbit survival and recruitment are linked to epidemiological and environmental conditions in their exotic range. Austral Ecology 37: 945–957.
- 47. Oli MK (2004) The fast-slow continuum and mammalian life-history patterns: an empirical evaluation. Basic and Applied Ecology 5: 449–463.
- 48. Beasley JC, Olson ZH, Dharmarajan G, Eagan TS, Rhodes OE (2011) Spatio-temporal variation in the demographic attributes of a generalist mesopredator. Landscape Ecology 26: 937–950.
- 49. Gehrt SD, Hubert GF, Ellis JA (2002) Long-term population trends of raccoons in Illinois. Wildlife Society Bulletin 30: 457–463.
- 50. Nixon CM, Mankin PC, Esker TL, Sullivan JB, Rothering AA, et al. (2009) Aspects of raccoon life history in west-central Illinois. Transactions of the Illinois State Academy of Science 102: 117–129.
- 51. Beasley JC, Beatty WS, Atwood TC, Johnson SR, Rhodes OE Jr (2012) A comparison of methods for estimating raccoon abundance: implications for disease vaccination programs. Journal of Wildlife Management 76: 1290–1297.
- 52. Ellis EC, Goldewijk KK, Siebert S, Lightman D, Ramankutty N (2010) Anthropogenic transformation of the biomes, 1700 to 2000. Global Ecology and Biogeography 19: 589–606.
- 53. Foley JA, DeFries R, Asner GP, Barford C, Bonan G, et al. (2005) Global consequences of land use. Science 309: 570–574.
- 54.
Bernstein L, Bosch P, Canziani O, Chen Z, Christ R, et al. (2007) Climate change 2007: synthesis report. An assessment of the Intergovernmental Panel on Climate Change. Valencia, Spain: IPCC.
- 55.
Brashares JS, Prugh LR, Stoner CJ, Epps CW (2010) Ecological and conservation implications of mesopredator release. In: Terborgh J, Estes JA, editors. Trophic cascades: predators, prey, and the changing dynamics of nature. Washington, D.C.: Island Press. 221–240.