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Changes in Distribution and Abundance of Anuran Species of Staten Island, NY, Over the Last Century
Beth Nicholls, Lisa L. Manne, and Richard R. Veit

Northeastern Naturalist, Volume 24, Issue 1 (2017): 65–81

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Northeastern Naturalist Vol. 24, No. 1 B. Nicholls, L.L. Manne, and R.R. Veit 2017 65 2017 NORTHEASTERN NATURALIST 24(1):65–81 Changes in Distribution and Abundance of Anuran Species of Staten Island, NY, Over the Last Century Beth Nicholls1,2,*, Lisa L. Manne1,3, and Richard R. Veit1,3 Abstract - The global decline of amphibian species is a pressing problem that has garnered much scientific attention. Annual fluctuations of amphibian populations are a common occurrence due to weather variability, reproductive failure, or other factors. Therefore, a long-term perspective through the use of historical datasets is needed to identify persistent trends. To examine the changes in the populations of Anuran (frog and toad) species in Staten Island, NY, we used the detailed notes contained in the field journals of naturalist William T. Davis (1862–1945) to form a basis of comparison to modern surveys (2010– 2011). We found very substantial changes, mainly declines, in the amphibian biota of Staten Island. Of the 10 original species, 4 have apparently been extirpated and another 4 have declined in probability of occurrence (PO), most notably Anaxyrus fowleri (Fowler’s Toad), whose PO decreased 1 order of magnitude. Only Lithobates clamitans (Green Frog) and Lithobates catesbeianus (Bullfrog) have increased through time. We show that these changes are related to environmental perturbations that have occurred over the same time period. Introduction There has been a rapid, global decline in amphibian populations over the last 50 years, leaving an estimated one-third of all species threatened with extinction (Stuart et al. 2004). A greater proportion of amphibian species are threatened than any other vertebrate class because of their sensitivity to the environment (Beebee and Griffiths 2005). Their moist skin allows oxygen absorption but also increases their susceptibility to toxin absorption (Collins and Crump 2009). The gelatinous eggs are not protected by a shell and often experience desiccation (Dickerson 1969). Amphibians’ physiological constraints such as being small-bodied and slow-moving compared to most vertebrates limit them further (Babbitt 2005, Gibbs 1998, Trenham et al. 2003). These factors make amphibians prone to local extinction, especially if their habitat is heavily impacted by anthropogenic activities (Trenham et al. 2003). Land-use change causes local and regional extinction of populations by eliminating individual organisms, destroying habitat, preventing access of animals to breeding sites and/or modifying the habitat’s critical biotic and abiotic properties such as temperature, food availability, and refuge sites (Cushman 2006, Knutson et al. 1999). Urban areas are characterized by chemical, light, and noise pollution, as well as an altered stream hydrology that negatively impacts many amphibians 1City University of New York / College of Staten Island, 2800 Victory Blvd, Staten Island, NY 10314. 2Current address - New York City Department of Parks and Recreation 200 Nevada Ave, Staten Island, NY 10306. 3Biology Program, Graduate Center, City University of New York, New York, NY 10016. *Corresponding author - Bethnicholls828@gmail.com. Manuscript Editor: Joseph Rachlin Northeastern Naturalist 66 B. Nicholls, L.L. Manne, and R.R. Veit 2017 Vol. 24, No. 1 (Barrett and Guyer 2008). Furthermore, the upland forests and emergent wetlands that are positively associated with Anurans are not available in an urbanized environment (Knutson et al. 1999). Annual fluctuations in amphibian populations are a common occurrence due to weather variability, reproductive failure, or other factors. Therefore the use of longterm data sets is necessary in order to understand persistent patterns in amphibian population variation (Blaustein et al. 1994, Brodman 2008, Busby and Parmelee 1996, Whiteman and Wissinger 2005). Organizations such as the North American Amphibian Monitoring Program and the Amphibian Research Monitoring Initiative are carrying out ongoing breeding-call monitoring programs to quantify trends in Anuran populations throughout North America (Weir and Mossman 2005). Despite these research efforts, there is still an overall dearth of baseline data that can be used to quantify changes in amphibian populations over short or long timescales (Gibbs et al. 2005). In order to gain a historical perspective, some studies have examined preserved museum specimens (Boundy 2005, Lehtinen 2002) or old field guides and maps (Cooke and Arnold 1982) to acquire historic amphibian data. This practice is not confined to amphibians, as the use of historical journals for scientific comparison has been completed for a variety of taxa, e.g., plants (Primack and Miller-Rushing 2012), birds (Vitale and Schlesinger 2011), and large marine animals (Lotze and Worm 2009). Gibbs et al. (2005) published a study of amphibian population changes in New York State, contrasting regional vs. local population changes. They found little change in population sizes at the regional scale, though habitat destruction has been extensive. At the local scale, several species declined, due to changes in habitat amount or configuration. Our study region has seen a substantial decline in the amount of its historic wetlands; ~2/3 of Staten Island’s coastal wetlands that existed in 1870 were destroyed by the mid-1990s (Tiner 2000). Compared to other similarly sized plots in New York State (Gibbs et al. 2005), we expected to find more dramatic declines in frog abundance on Staten Island, due insularity of the location, the magnitude of habitat degradation that has occurred, and the longer time for habitat alteration impacts to be felt. It is a short distance in human terms to cross the narrow tidal strait between Staten Island and New Jersey. However, to an animal with limited dispersal capability, the distance is often insurmountable. In this analysis, we exploited data contained in the field journal of naturalist William T. Davis (1862–1945) as a historical baseline of Anuran populations. A self-taught natural historian, Davis is particularly well-known for his interest in insects: he discovered Manomera blatchleyi atlantica Davis (Eastern Walking Stick Insect) and was internationally known as an expert on periodical cicadas (genus: Magicicada) (Abbott 1949, Davis 1923). He conducted intensive field work on Staten Island, NY, from the late 1800s to the mid-1930s, documenting species occurrences (Anuran and otherwise). Davis recorded 10 Anuran species in his journals: Pseudacris crucifer Wield- Neuwied (Spring Peeper), Hyla versicolor LeConte (Gray Treefrog), Lithobates sylvaticus (LeConte) (Wood Frog), Acris crepitans Baird (Northern Cricket Frog), Northeastern Naturalist Vol. 24, No. 1 B. Nicholls, L.L. Manne, and R.R. Veit 2017 67 Lithobates palustris (LeConte) (Pickerel Frog), Lithobates kauffeldi (Feinberg et al., 2014) (Atlantic Coast Leopard Frog), Anaxyrus fowleri (Hinckley) (Fowler’s Toad), Lithobates clamitans (Latreille) (Green Frog), Lithobates catesbeianus (Shaw) (Bullfrog), and Pseudacris kalmi Harper (New Jersey Chorus Frog). Spring Peeper. The Spring Peeper is a habitat generalist common in forested areas and suburban settings but less persistent in areas surrounded by commercial land use due to the loss of breeding pools or upland habitat (Gibbs et al. 2005, 2007). Given the loss of aquatic area in Staten island, we expected this species to have suffered some loss in distribution over the years of our study. Gray Treefrog. Gray Treefrogs prefer to live in moist deciduous woodlands and areas with well-established, clustered wetlands surrounded by woody vegetation (Gibbs et al. 2007, Pillsbury and Miller 2008). This species should also have declined due to the loss in aquatic habitat in Staten Island (Tiner 2000). Wood Frog. Wood Frogs are a terrestrial species that prefers heavily forested areas with the presence of a herbaceous layer (Klemens 1993). Wood Frogs are not tolerant of habitat fragmentation, which reduces their dispersal rate because they avoid crossing fields, lawns, and roads (Cushman 2006). Wood Frogs breed most successfully in vernal pools instead of lakes or ponds (Calbom 2004). We expected this species to have declined due to fragmentation of forests and loss of vernal pools on Staten Island. Northern Cricket Frog. Northern Cricket Frogs are terrestrial and semi aquatic, occurring in a variety of fresh water habitats, although they are very rarely found at large lakes (Gray and Brown 2005). This species is negatively affected by low pH, and if a breeding or overwintering site becomes inaccessible or marginal through pesticide use or acidification, the associated population of Northern Cricket Frogs is likely to become extinct in that area (Lehtinen and Skinner 2006). The Northern Cricket Frog is classified as endangered in New York State (Gibbs et al. 2007). We expected this species to have declined due to habitat sensitivity and the widespread changes in the environment. Pickerel Frog. Pickerel Frogs are found around streams and wetlands as one common name, “swamp frog”, and its scientific epithet, palustris, suggest (Gibbs et al. 2007). When not breeding, Pickerel Frogs can be found in meadows, fields, and damp woods, foraging in wet, weedy areas, and using stream beds as habitat corridors (Gibbs 1998). We expected this species to have declined due to the loss of terrestrial and aquatic habitat (Tiner 2000). Atlantic Coast Leopard Frog. Atlantic Coast Leopard Frogs are known to persist in large wetland complexes rather than isolated wetland patches (Feinberg et al. 2014). Due to Leopard Frog’s specific habitat needs including preference for open-canopied marshes and wet meadows, which are becoming rare on Staten Island, we predicted that the species has decreased over time. Fowler’s Toad. Fowler’s Toads are Staten Island’s only toad species. The habitat of Fowler’s Toads includes beaches, lake shores, fields, gardens and roadsides with sandy soil (Wright and Wright 1995). Fowler’s Toads lay an average of 3500 eggs, and less than 0.1% of the eggs will survive to the age of first reproduction (Green Northeastern Naturalist 68 B. Nicholls, L.L. Manne, and R.R. Veit 2017 Vol. 24, No. 1 2005). Survival of breeding adults is essential for the continuation of this species because mortality is high for the tadpoles and post-metamorphic juveniles (Green 1997). We expected this species to have declined due to its preference of habitat along beaches, fields, and pastures that have experienced significant fragmentation over time. Green Frog. Green Frogs can live and breed in many different habitats including swamps, large ponds and reservoirs, as well as smaller water bodies and pools (Wright and Wright 1995). We expected this species to have maintained a steady population size through time due to its relatively general habitat needs. Bullfrog. Bullfrogs have a powerful influence on the surrounding Anuran composition, affecting both species richness and diversity and becoming invasive in new environments (Clarkson and DeVos 1986, Gibbs et al. 2007, Moyle 1973). Pillsbury and Miller (2008) found that Bullfrogs are more resilient to urban fragmentation than most of the Anuran community. In addition to urbanized ponds, Bullfrogs can also live in habitats that may be unsuitable to other frogs such as created wetlands and golf course ponds (Adams 2000, Boone et al. 2008). We hypothesized that this species should have increased over time because of its adaptability to urbanization. New Jersey Chorus Frog. Davis found only a small isolated population of the New Jersey Chorus Frog in 1 marsh between the years 1901 and 1910 (Davis 1910a). We did not include the population in further analysis due to its small population size in Davis’ time. Davis’ (1899, 1901, 1902, 1908, 1910a, 1931, 1934, 1935) notebooks provide a detailed database of the historical distribution of flora and fauna, and we have used these data to form a basis of comparison to contemporary data collected during the period 2010–2011. We used a Bayesian analysis of frequency of occurrence to determine which (if any) amphibian species have shown changes in abundance and occurrence over the intervening time. We hypothesized that our study would show most Anuran species to have declined over time due to the habitat changes, Green Frog will have maintained a steady population size, and Bullfrog to have increased over the years. To our knowledge, this is the first such analysis of this type (utilizing data from a century previous) for amphibians. Field-Site Description Staten Island, NY, is one of the 5 boroughs of New York City and the southernmost point of New York State. Due to its insular nature, Staten Island remained isolated from the rest of the city until the 1950s, and retained a bucolic quality long after the surrounding areas saw an increase in population and widespread habitat destruction. Staten Island’s human population growth has increased dramatically, at a rate of 6.12% per year between 1880 and 1930 (the time span of Davis’ journals) and 2.45% per year between 1930 and 2010, with a 2010 population of 468,730 (US Census 2010). Staten Island has lost a considerable amount of its historic wetlands (Tiner 2000). Furthermore, many ponds were drained or altered for aesthetic or functional purposes (Dickenson 2002, Weingartner 1965). Northeastern Naturalist Vol. 24, No. 1 B. Nicholls, L.L. Manne, and R.R. Veit 2017 69 Methods Historical data We compiled a historical baseline from the journals of naturalist William T. Davis composed between the years 1880–1938. From the 5000 pages of journal entries, we recorded the date and location of every frog noted by Davis, detected through call or by sight, assuming that all species present were recorded. Davis noted that he eventually visually confirmed the great majority of occurrences that were initially detected by call. Any stated absence of a frog species by Davis was considered to be a visit to a site, and we incorporated these into the analysis as well. We then located all of Davis’ frog sightings on a historical Staten Island map and subdivided the map using natural or other long-standing features (e.g., creeks or Figure 1. Fourteen subdivisions of Staten Island used for comparison of 2 time periods: (1) Arlington, (2) Clove Valley, (3) North, (4) Watchogue, (5) Willowbrook, (6) Egbertville, (7) Moravian, (8) Todt Hill, (9) East, (10) Woodrow, (11) Richmond, (12) Beach, (13) South, and (14) Southeast. Northeastern Naturalist 70 B. Nicholls, L.L. Manne, and R.R. Veit 2017 Vol. 24, No. 1 roads) as borders around these clusters of data, with each subdivision having an average of 12 historical data points (14 subdivisions total; Fig. 1). Even though much of Staten Island’s landscape has changed over time, the borders of the island and the inner subdivisions we created have remained constant, and thus serving well as a set of standardized areas in which to complete a long-term study. When using historical sources for scientific research, there will always be some ambiguity, whether in locations, methods, or species identifications, which limits the quantity of data (Primack and Miller-Rushing 2012). In this particular study, the seasonality of the calls in Davis’ data could not be determined, therefore we combined Davis’ observations during the spring and summer months when frogs are the most active (March–September) for this analysis. We likewise combined data from all contemporary visits conducted by B. Nicholls (see below in Contemporary data subsection) during March through September before being incorporated in the analysis, to maintain consistency with the historical data. Contemporary data: Breeding-call surveys During the spring and summer of 2010 and 2011, B. Nicholls searched for amphibians on Staten Island using breeding-call surveys according to the protocol of the North American Amphibian Monitoring Program (NAAMP; Weir and Mossman 2005). The NAAMP protocol is a transect census that entails driving along a roadside route and stopping at 10–15 pre-determined sites (potential breeding sites) that are at least 0.8 km apart to listen for breeding calls at 5-minute intervals. We established 10 roadside routes in this study. In addition, we also surveyed major wetlands and water bodies in Staten Island parklands at 5-minute intervals. Figure 2 is a map of all the breeding-call survey sites (n = 150). Each site was sampled at least twice during the 6-month breeding season, but most sites were sampled more frequently, with an average of 8.5 visits per site, for a total of 200 field hours. Repetitive monitoring throughout the season was required because the breeding phenology varies among species, and more frequent surveying increases the ability to detect presence (Storfer 2003). There are some species, classified as early breeders, that mate and reproduce in March (e.g., Spring Peepers) while others are considered to be late breeders, whose reproduction occurs in June or July (e.g., Bullfrogs) (Dickerson 1969). By the end of the season, species accumulation curves had leveled off for all sites, indicating that we had found all species that were present. The significance of Davis’ data is due to its longevity (nearly 60 years) and comprehensiveness within a small insular area. We attempted to duplicate the scope and extent of his dataset in a 2-year period using the established protocol of the NAAMP. Our method covers the same area but using a more rapid and focused technique. Statistical analysis We used Bayesian methods to analyze these data. Bayesian analysis uses a “prior” probability distribution as a null expectation. We generated this prior distribution (a probability of occurrence, calculated as the probability of encountering the species across all of Davis’ visits to different Staten Island sites). We then updated this prior distribution with experimental or current data, to generate a Northeastern Naturalist Vol. 24, No. 1 B. Nicholls, L.L. Manne, and R.R. Veit 2017 71 “posterior” probability distribution. The data recorded by William T. Davis served as a unique prior probability of occurrence, though it might be an overestimate of likelihood of occurrence, if Davis visited sites (and didn’t find any frogs) without adding a notation in his field journal. We calculated the mean probability of occurrence (PO) for each species noted by Davis for all 14 subdivisions: PO = number visits with a positive detection for a species total number of visits in subdivision) The probability of occurrence is on a scale from 0 to 1. Davis’ data act as a control, and these prior values should change if the surrounding conditions change. Therefore, shifts in species abundances through time will be reflected by changes in probability of occurrence through time. We used the computer software program WinBUGS version 1.4.3 to analyze the data (Spiegelhalter et al. 2003). Through simulation, WinBUGs samples from a posterior distribution via Markov Chain Monte Carlo methods and estimates the PO of uncertain events (Ntzoufras 2009). Results Of 9 species analyzed in the Bayesian analysis (New Jersey Chorus Frog being recorded by Davis but not analyzed here), 2 have increased in PO and 7 have Figure 2. Present day (2010–2011) anuran sampling sites located along roads and in the parklands on Staten Island. Northeastern Naturalist 72 B. Nicholls, L.L. Manne, and R.R. Veit 2017 Vol. 24, No. 1 decreased in PO (Figs. 3, 4). Figure 3 gives the frequency distribution of PO for all species and both time periods. Figure 4 shows the resulting most likely rate of increase or decrease in PO for all 9 species as revealed by WinBUGS. Extirpated or almost-extirpated. A few species were extirpated on Staten Island over the period of this study. Wood Frogs were once very abundant according to Davis (Davis 1899), but neither Wood Frogs, Pickerel Frogs, nor Northern Cricket Frogs were found in the present time in this study (Figs. 3, 4). The latter were once abundant according to Davis’ journal references (Figs. 3, 4). He Figure 3. Frequency distributions of probabilities of occurrence (PO) from Davis’ time (prior, left) and contemporary PO (posterior, right). The 2 species with increasing probabilities of occurrence are at the bottom of the figure. Northeastern Naturalist Vol. 24, No. 1 B. Nicholls, L.L. Manne, and R.R. Veit 2017 73 mentions hearing an “astounding number of Cricket Frogs” in 1902 (Davis 1902) and was still reporting “many” Northern Cricket Frogs in 1935 (Davis 1935). In addition, Atlantic Coast Leopard Frogs have decreased since Davis’ time (Figs. 3 ,4) and were believed to be extirpated for years until a small population was found in a remote location on Staten Island (Johnson and Johnson 1998); we also found small numbers of this species. Near only 5% PO in present-day. Fowler’s Toads demonstrated the greatest decline in PO among extant species: a decrease from 0.3 in Davis’ time to 0.0285 today (Figs. 3, 4). Even though Fowler’s Toads were found in several locations on Staten Island in 2010–2011, the population at most of these sites was relatively small based on the frequency and intensity of the breeding calls. In most cases, calling was sporadic. The magnitude of Gray Treefrog decline on Staten Island is the 3rd-largest, though they were declining in Davis’ lifetime as well. They linger on at 0.05 PO. Declining but still relatively widespread. Spring Peepers have declined (Figs. 3, 4) yet are still widespread and abundant in some areas on Staten Island. Because of their small size, populations of Spring Peepers are able to live in small patches of habitat that remain even in the face of habitat fragmentation. Spring Peepers were completely missing in contemporary surveys from the urbanized section of Staten Island’s north shore. Increasing. Both Bullfrogs and Green Frogs have increased in PO over time on Staten Island (Figs. 3, 4). We were surprised by the latter, but not the former. According to Davis’ records, Bullfrogs were not detected on Staten Island before 1896 (unlikely to have been an oversight, given their loud breeding call), and thus Bullfrogs have been introduced to the island and have since increased (Davis 1899). Discussion There was an overall decrease in the PO among the 9 Anuran species included in this study (Fig. 4). We noted declines in Northern Cricket Frogs, Atlantic Coast Leopard Frogs, Wood Frogs, Pickerel Frogs, Fowler’s Toads, Gray Treefrogs, and Spring Peepers. Of all extant species, Fowler’s Toads demonstrated the greatest Figure 4. The change in probability of occurrence of 9 anuran species from Davis’ historical records (late 1800s–early 1900s) to present day. Northeastern Naturalist 74 B. Nicholls, L.L. Manne, and R.R. Veit 2017 Vol. 24, No. 1 decline in PO: a decrease from 0.3 in Davis’ time to 0.0285 today. We did not find Wood Frogs, Northern Cricket Frogs, or Pickerel Frogs in the contemporary survey, and we believe them to be extirpated on Staten Island. We expected an increase for Bullfrogs because they are the largest North American amphibian, consume a variety of prey (including other frogs), and are quite generalized in their habits (Clarkson and DeVos 1986, Gibbs et al. 2007, Kupferberg 1997, Moyle 1973, Smith 1977). Although we did not predict the increase of Green Frogs, this result is perhaps unsurprising in retrospect since Green Frogs are one of New York State’s most common species and thrive in areas modified by humans (Gibbs et al. 2007). Both Bullfrogs and Green Frogs inhabit large and permanent ponds and wetlands. These permanent ponds and wetlands are preserved, restored, or created for aesthetic or functional purposes in greater proportions than other water bodies, e.g., permanent wetlands receive more protection than ephemeral ponds due to legislation such as the Clean Water Act (Adams 2000, Miller and Klemens 2005, Pearson 2008). Bullfrogs are rarely observed out of their aquatic habitat, so the loss of upland habitat characteristic of urban/suburban ponds has little effect on them (Bury and Whelan 1984, Pyburn 1958). For example, Pillsbury and Miller (2008) found that Bullfrogs are more resilient to urban fragmentation-created wetlands and golf course ponds (Adams 2000, Boone et al. 2008). In addition, the tadpoles of Green Frogs and Bullfrogs overwinter in these protected aquatic habitats, allowing them to have a long larval period and reach a greater size before metamorphosis, increasing their competitive ability with other Anuran tadpoles (Skelly et al. 1999). Furthermore, the tadpoles of these species are not palatable to fish, a major predator of other Anurans (Semlitsch 2002, Skelly et al. 1999). Staten Island’s other amphibians have suffered a loss of both terrestrial and aquatic habitat over the last century. The major causes of deforestation of the terrestrial habitat on Staten Island have included farming and both commercial and residential development. The terrestrial habitat on Staten Island has been fragmented due to Staten Island’s long agricultural history (Robinson et al. 1994). Starting in the early 1900s, roads were cut through the forested areas, and urbanization steadlily spread through the island, first occurring near the ferry terminals (Robinson et al. 1994). Fires have been an agent for habitat destruction for over 100 years; some were set as a means of mosquito control and others were started by a careless mistake (Davis 1910b). One study quantified that over 40% of Staten Island’s original native plant species have been extirpated due to broad-scale habitat alterations (Robinson et al. 1994). Habitat loss likely played a role in the decline and local extirpation of Pickerel Frogs. Mathewson (1955) recorded that Pickerel Frogs were once common on Staten Island in open moist meadows and along the borders of the marshes in the Fresh Kills area. Therefore, Pickerel Frogs may have been negatively affected by the habitat loss or contamination surrounding the Fresh Kills landfill in addition to the general loss of meadows on Staten Island for development. This contrasts with Pickerel Frog populations in the greater New York State, which are quite widespread (Gibbs et al. 2007). Northeastern Naturalist Vol. 24, No. 1 B. Nicholls, L.L. Manne, and R.R. Veit 2017 75 Habitat fragmentation has certainly been an endangering factor for Anurans of Staten Island. Generally, areas with a high concentration of roads have high Anuran mortality when frogs migrate between breeding and non-breeding areas (Knutson et al. 1999). Historically, Fowler’s Toads were very widespread and abundant on Staten Island. Davis even recorded in his journal: “The toads were so numerous that I could not walk in place near the ponds without injuring some of them” (Davis 1901). Davis’ (1908) field notes indicated that many adult toads suffered road mortality with the advent of the automobile. Additionally, large numbers of migrating Wood Frog adults have been killed when crossing roads between terrestrial habitats and breeding sites (Fahrig et al. 1995, Pillsbury and Miller 2008). Abundance of Fowler’s Toads and Wood Frogs can vary regionally, and in some places in New York State both are still abundant (Gibbs et al. 2005, 2007). Many ponds were drained or altered for aesthetic or functional purposes. Of the 112 ponds that existed in early atlases of Staten Island (1887–1917), only 31 remained by 1965 (Weingartner 1965). The natural process of succession has modified those ponds, but many unnatural ponds have also been created for aesthetic or functional purposes (Birx-Raybuck et al. 2010). When ponds are created or modified for aesthetic reasons, existing marshy habitat utilized by frog species are often removed (Campbell and Noyes 1973). For example, lakes that were spring-fed were deepened and dammed (Weingartner 1965). Water was pumped from natural ponds and swamps (Abbott 1949). Furthermore, the 8 mills on Staten Island altered the hydrology of the island in the past (Salmon 2003). When streams are altered and dammed, wetlands associated with these water courses may be affected or lost all together (Campbell and Noyes 1973). All these modifications often affect the natural hydroperiod or the period of time that a pond is inundated with water. A change in hydrology will affect some amphibians favorably while restricting other species from flourishing in that particular environment. The draining of natural ponds, marshes, and swamps was a common practice of mosquito control in the 1930s. In addition, oil was poured into marshes in an unsuccessful attempt to control the mosquito populations (Johnson 1997). The New York City Department of Health and Mental Hygiene presently conducts aerial spraying for mosquito control during the West Nile virus season (April–October), treating 140,000 catch basins city wide (NYC 2016). These chemical pesticides are absorbed through the skin of amphibians (Bruhl et al. 2011). It has been shown that pesticides have direct and indirect effects on Anuran species by killing them outright, affecting behavior, reducing growth, or acting as endocrine disruptors (Hayes 2004, Relyea 2005). Declines of Anurans on Staten Island may reflect similar declines at the regional scale. Leopard frog declines have been observed in Staten Island, Connecticut, New Jersey and other parts of New York State (Gibbs et al. 2007, Klemens 1993). The conservation efforts in the tri-state have been complicated in the past due to confusion surrounding the taxonomy of leopard frog species including Lithobates pipiens Schreber (Northern Leopard Frog) and Lithobates sphenocephalus Cope (Southern Leopard Frog) (Kauffeld 1936, 1937; Newman et al. 2012). Scientists recently Northeastern Naturalist 76 B. Nicholls, L.L. Manne, and R.R. Veit 2017 Vol. 24, No. 1 determined that the leopard frogs on Staten Island were a third, cryptic species, Lithobates kauffeldi (Atlantic Coast Leopard Frog; Feinberg et al. 2014, Newman et al. 2012). The Atlantic Coast Leopard Frog was the species found on Staten Island historically, and its range has constricted over time (Feinberg et al. 2014). Northern Cricket Frogs have been declining in New York State since the 1940s. This species is now considered to be endangered statewide and continue to decline in many parts of its range (Gibbs et al. 2007, Lehtinen 2002). In addition, the presence of Bullfrogs on Staten Island may have played a role in this species’ decline, since Bullfrogs are known predators of Northern Cricket Frogs (Gray and Brown 2005). Although Wood Frogs can suffer wild population fluctuations and are currently declining, these fluctuations might be counteracted by their dispersal ability (Gray and Brown 2005). Wood Frogs disperse further than other species of frog and are often found far from a water source (Baldwin et al. 2006). However, their vulnerability to cars on roads and to loss of vernal pools and forests may be their undoing on Staten Island. The probabilities of occurrence shown in Figures 3 and 4 mask a bit of historical variation in Gray Treefrog population sizes. Despite their tolerance to suburban habitat changes, Gray Treefrog populations decreased during Davis’ lifetime (Davis 1934, 1935). The decline continued through the 1950s, with the increase of the human population (Mathewson 1955). Gray Treefrogs were believed to be extirpated on Staten Island by 1966 but were re-introduced to Staten Island by the NYC Department of Parks and Recreation and have since spread (Nancy Zawada, New York City Parks Department, Staten Island, NY, unpubl. data.). This overall trend of decline contrasts with that of New York State, where Gray Treefrogs are increasing (Gibbs et al. 2005). In general, the conservation of amphibians on Staten Island is a dire issue due to the limitations of island biogeography; re-colonization of Staten Island, an oceanic island, is near impossible for Anurans sensitive to the saltwater barrier that surrounds the island. Since these species move significantly shorter distances than other tetrapods, they are capable of gene exchange only between nearby ponds and microhabitats, and depending on the extent of isolation, re-colonization following extirpation is rare without human intervention (Blaustein et al. 1994). With gene flow restricted to occur within Staten Island’s borders, it is critical to maintain landscape connectivity because seasonal amphibian migration is essential for sustaining viable populations. The habitat destruction and alteration on Staten Island has favored the more aquatic species including Bullfrogs and Green Frogs. Compared to the habitat specialists, these species have thus far fared better in human-altered environments. Overall, there were more species declines in this study compared to the Gibbs et al. (2005) study of New York State; however, our study is over a longer time frame and limited to a small, insular area. Therefore, this study is a natural experiment of how disastrous habitat alteration can be over time, especially when incorporating the effects of insularity, urbanization, fragmentation and pesticide use. This study Northeastern Naturalist Vol. 24, No. 1 B. Nicholls, L.L. Manne, and R.R. Veit 2017 77 foreshadows these impacts for other fragmented landscapes within New York State and beyond. Acknowledgments We are indebted to William T. Davis, for without his dedication and foresight, this study would not have been possible. We thank the Staten Island Museum for making William T. Davis’ journals available to us and for interpretation of older place names. We appreciate the assistance of all volunteers that helped to gather the contemporary frog survey data, especially P. Perone. In addition, we would like to thank A. Nicholls, G. Cronick, and J. Sutton for support, and the manuscript editor and 2 anonymous reviewers for helpful comments. Literature Cited Abbott, M. 1949. The Life of William T. Davis. Cornell University Press, Ithaca, NY. 319 pp. Adams, M.J. 2000. Pond permanence and the effects of exotic vertebrates on Anurans. Ecological Applications 10:559–568. Babbitt, K. 2005. 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