UNPUBLISHED PROOF INTRODUCTION

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1 R E S E A R C H A R T I C L E The Effects of Flooding Upon the Snake Fauna of an Isolated Refuge Owen J. Sexton 1 Wayne J. Drda Kenneth G. Sexton Washington University Department of Biology and Tyson Research Center P. O. Box 258 Eureka, MO Judith E. Bramble Environmental Science Program DePaul University Chicago, Illinois Corresponding author: sexton@biology.wustl.edu; Natural Areas Journal 27: ABSTRACT: The initial purpose of this study was to ascertain the species abundance of snakes inhabiting a 371 ha reconstructed marsh, the Marais Temps Clair Conservation Area in St. Charles County, Missouri. This flood-prone refuge is surrounded by agricultural lands and is upstream from the confluence of the Mississippi and Missouri rivers. Only eight species inhabit the study area. The abundance of all eight species declined dramatically after major flooding of both rivers in Subsequent major flooding in 1995 had little additional effect. The proportion of pre-flood resident species at our site to the number of non-resident species known to occur in the surrounding county was significantly lower than similar ratios at other conservation areas in nearby Missouri and Illinois. Resident species at our site were more likely to be semi-aquatic and arboreal than species found in the surrounding county, and post-flood survivors were significantly larger than pre-flood individuals. We attribute two mechanisms for the unexpectedly low species diversity: (1) the effects of major flooding, and (2) the reduction of immigration access from the area surrounding the study area following Euro-American settlement. We recommend that isolated flood-prone refuges should be provided with internal or peripheral islands that would mitigate the effect of flooding upon local species diversity by serving as a lifeboat to increase survivorship of resident populations and as a landfall for flood-borne individuals swept downstream from upstream sources. Index terms: corridors, flooding, isolation, refuge design, snake community INTRODUCTION Michener and Hauber (1998) described the effect of floods upon humans in the United States between 1990 and They pointed out that our scientific understanding of different types of natural disturbances is directly proportional to their frequency and inversely proportional to their amplitude. For example, little is known about the effect of infrequent large scale flooding because any such event may not occur at a particular site during the professional life of an interested scientist. They continue by stating that short-lived ecological responses to flooding are often overlooked, and scientists are rarely able to take full advantage of the research opportunities offered by these rare events. Obviously, such flood events effect species other than humans. The serendipitous study reported here will describe the effect of the massive floods of 1993 and 1995 upon eight species of colubrid snakes which inhabited an isolated wildlife refuge located in the lowlands between the Missouri and Mississippi rivers, a short distance upstream of their confluence. The study began in 1990, terminated in 2000, and underwent three stages. The initial goal was to determine if the western fox snake (Elaphe vulpina vulpina) inhabited the Marais Temps Clair Conservation Area (hereafter MTC), a reconstructed wetlands with associated woodlots and fields. This species was of particular interest to the sponsoring state agency, the Missouri Department of Conservation, because this site is located at the southernmost limit of the species geographic distribution (Powell 1990). Secondly, we quickly expanded our study to include all species of snakes we collected at MTC. Serendipitously, these field studies were terminated in July 1993, just a week before the massive floods of the Mississippi and Missouri rivers. The third stage was initiated after the retreat of the 1993 flood, when we seized the opportunity to repeat our sampling procedures to determine the effect of the 1993 flood upon the snake community. The 1995 flood interrupted these efforts again. After the cessation of that flood, we again assayed changes in the abundance of the eight species of snakes during 1996 and Johnson (2000) recorded 23 species of snakes known to occur, or to have occurred historically, in the surrounding county of St. Charles. The contiguity of the MTC area with the surrounding landscape was disrupted by Euro-American development from the 1700s until the present. Compounded by periodic flooding, we expected the snake community to be a subset of this potential pool of species, and hypothesized that species found at MTC would be more likely to possess characteristics that would enable individuals to either survive flooding or to recolonize MTC from surrounding areas following a flooding event. The heavy flooding of 1993 and 1995 offered us an opportunity to determine if such character- Volume 27 (2), 2007 Natural Areas Journal 133

2 istics were associated with the successful recolonization of the snake fauna into this isolated preserve. Characteristics that we initially hypothesized to be important for success at MTC included semi-aquatic and arboreal habits and large body size. Semi-aquatic species have some level of dependence upon aquatic resources. For example, Nerodia sipedon and N. rhombifer, Thamnophis sirtalis and T. proximus, and Regina grahamii are dependent upon aquatic resources for all or much of their food (Ernst and Barbour 1989). Individuals of these species and of Elaphe vulpina, which regularly exploits the immediate environs of aquatic systems, should all be more successful than more terrestrial species in surviving and/or recolonizing periodically flooded habitats. Whereas individuals of most species of snakes can climb to some limited extent, species that regularly exploit vegetation above ground level as a source of food in the form of arboreal prey, as basking sites or as refuges from predators may be more likely to seek arboreal refugia during flooding events. Finally, within any population, larger individuals would be better able to resist transport out of their residence area or to attain downstream refugia because of possessing greater strength than smaller individuals. METHODS Location MTC is located within the Township of Portage des Sioux (46 North, Range 5 East and 48 North, Range 6 East). Geographically it is situated at 90 o 25 W, 38 o 54 N. MTC is located on a triangular peninsula historically referred to as the Point between the Mississippi River and the Missouri River in St. Charles County, Missouri (Figure 1; Williams 1875). The western base of the Point is situated on low hills on the north bank of the Missouri River at the site of the City of St. Charles, and it extends eastward for approximately 40 km overland to the confluence of the two rivers (Figure 1). MTC is situated in the lowlands of the Point, roughly half way between the western hills and the confluence to the east. It is 37-river km upstream along the Missouri River, 4 km south of the Mississippi River, and 6.4 km north of the Missouri River. Maximum elevation Figure 1. Marais Temps Clair is located on the peninsula called the Point, upstream of the confluence of the Mississippi River (to the north) and the Missouri River (to the south). This map of St. Charles County in 1875 (Williams 1875) illustrates the early configuration of MTC (R5 sect. 24, 26). The map depicts the initial encroachment of Euro-American settlement upon MTC beginning the with settlement of St. Charles (southwest corner) in 1769 and of Portage Des Sioux (south bank of the Mississippi) in The common grounds of the settlers at those times already extended out towards MTC. By the 1880 s other towns, surrounding farms, roads, and railroads further isolated the study area from contact with upstream sources of immigrants. 134 Natural Areas Journal Volume 27 (2), 2007

3 of the MTC is approximately 128 m. The maximum elevation of the nearest of the St. Charles hills west of MTC is 179 m. The Missouri Department of Conservation obtained the 371-ha site in 1979 to provide suitable habitats for migratory and residential birds and opportunities for hunting, fishing, and passive recreation such as bird watching and hiking. The area of MTC has been parceled among different usages (Figure 2) to implement management goals. One major goal is to manipulate the water level within a series of 10 pools, each surrounded by a leveelike dirt impoundment, for the benefit of migratory waterfowl. Water depth within the pools is regulated by wells supplying water and drains to lower water levels. High water is present in spring and fall, low water in summer. The low water levels enable the growth of food plants for waterfowl. Even at normal high water levels, the water surface remained 3 m below the levee tops. After spring drawdown, most of the levee sides were exposed, and later in the hot season, the evaporation of water further reduced water depths to the extent that some or parts of pond bottoms became exposed to the air. Grasses and forbs grew on the upper sides and tops of the levees. Some of the upland fields were devoted to corn and soybeans, but the rest remained uncultivated. There are three small remnant forests. An active railroad right-of-way adjoins the southern boundary (Figure 2). A marsh of approximately the same size as MTC continues eastward from MTC and is owned by a private hunting club. The landscape surrounding MTC and the hunting club marsh is completely devoted to large-scale agriculture. The principal crops are corn, wheat, and soybeans. Indeed, farming dominates all of the Point so that MTC is an island isolated from any ready source of immigrant snakes, save those carried by floodwaters. Quantitative sampling We sampled all habitats (Table 1) within MTC by utilizing hide boards and hand capture. Hide boards (Grant et al. 1992) are plywood boards, 0.6 m x 0.6 m, that are placed flat on the ground. Snakes take Figure 2. The Marais Temps Clair Conservation Area is currently organized around pools that are surrounded by levees. Compare the numbered pools to the earlier configuration of the multi-fingered lake of Figure 1. The numbered black dots indicate the location of the hide boards. Original map executed by the Missouri Department of Conservation. Copyright 2005 by the Conservation Commission of the State of Missouri. Used with permission. refuge beneath the boards, which may be left unattended because the snakes are free to come and go without restraint. We set out 60 boards from 1990 to 1996, inclusive, and 31 boards in The latter array was placed in the most productive sites of We attempted to visit each board on most sampling days. Hand capture was dependent upon sighting snakes that were not beneath hide boards as we traveled across MTC on foot or by car. After each capture, we recorded the species, time and date of capture, location (specific hide board or location of visual sighting), snoutvent length (SVL), and total body length. We also individually marked each captured snake by clipping sub-caudal scales. All animals were released immediately after examination and marking (for new individuals) at the point of capture. In the data analysis presented here, we only used the first capture of any individual snake and Volume 27 (2), 2007 Natural Areas Journal 135

4 Table 1. Areas of habitats recognized by the Missouri Department of Conservation at Marais Temps Claire Conservation Area St. Charles County Missouri USA and number, location and yearly distribution of hide boards during the study. N = number of hide boards. none from subsequent captures. Data for each species were normalized as number of captures per 100 h of effort. Description of flooding The extent and duration of the 1993 and 1995 floods were based upon the daily records recorded at gauges maintained by the U.S. Army Corps of Engineers at Grafton, Illinois, for the Mississippi River and at St. Charles, Missouri, for the Missouri River. Grafton is 7.4 km upstream of MTC, and St. Charles is 15.3 km SSW of MTC. We refer to the three time periods as pre flood ( ), inter flood ( ), and post flood (1996 and 2000). Statistical analysis Area Percent of Boards Boards Habitat (ha) Total Area N Percent N Percent Non-forested Wetlands and Levees Croplands and Fields Bottomland Forest Pavement and Buildings Total Data were analyzed using SPSS (version 11.0) and Excel (version 9.0). Wilcoxon Signed Ranks Matched Pairs Test was used to evaluate the change in snake abundance from one time period to the next. Evaluation of the characteristics of snake species present at MTC and present in the surrounding county but absent at MTC was performed by t-test, multiple regression, and chi-square test. Comparison of MTC biodiversity to the biodiversity at other sites was performed by one sample t-test. In all statistical tests, an alpha of 0.05 was used; all tests were 2 tailed. RESULTS Flooding events The first evidence of high water in 1993 that we observed at MTC occurred on 27 April, although flooding had occurred earlier at both the Mississippi and Missouri rivers upstream gage stations (Figure 3). By 8 May, most of the pools at MTC were full, but higher flood levels occurred by mid-june. Waters temporally receded by 5 July but crested thereafter. A resident who lived just across Missouri Highway 94 at the northeast corner of MTC informed us that at flood maximum, water had covered the highway, a height of m above the tops of most MTC levees. On 12 September, some levees were still under water and the exposed levees were covered with deposited sediment. Water again rose so high by 1 October that we again could not reach MTC. By 3 October, water was at the level of 17 August, but receded below the tops of the levees by 12 October. On 14 March 1994, the MTC levees were above water but the lowlands within them were still flooded. In 1993, the Mississippi River reached 6.13 m above flood stage at the Grafton station; there were 203 days of flooding in three episodes. That same year at the St. Charles gauge, the Mississippi River reached a maximum of 4.40 m above flood stage with 142 days of flooding in eight episodes (Figure 3). Flooding began again by 20 May 1995 (Figure 3). On 29 May, the Missouri National Guard 1438 Engineering Company took us on board their emergency ferry for a survey of the depth of flooded areas at MTC. Readings on the ferry depth gauge indicated a maximum depth of water in Pool 9 (Figure 2) at 5.0 m; levee tops were 2.3 m below the water surface. The 1995 flood was the lesser of the two floods and, judging by earlier estimates of depth, we concluded that in 1993 at maximum flooding, the MTC levees had been 3.2 m below the water surface. On 11 June 1995, the water level had receded by 0.9 m, but the levees were not visible. By 2 July, water had receded m below the tops of the levees. In 1995, there were three flooding episodes recorded at the Mississippi gage station for a total of 60 days and three floods at the Missouri station for a total of 71 days (Figure 3). Maximum flood levels were lower in 1995 than 1993 (3.16 m on the Mississippi and 5.61 on the Missouri). In neither 1993 nor 1995 did the floods breach the levees, but the floods did overtop them. Effect of flooding on snake species abundance We made 204 visits to MTC to sample snakes throughout this study (Table 2). Sampling visits ranged from h, averaging 3.5 h/visit and eight boards examined per hour spent sampling. In 1993, sampling ended just before flooding. In 1994, the first three visits (6 h) were not included in the estimations of snake abundance, because the region was still 136 Natural Areas Journal Volume 27 (2), 2007

5 Figure 3. Variations in water levels of the Missouri River at St. Charles, Mo. and for the Mississippi at Grafton, IL. during 1993 and Dashed line represents flood stage. very much under post flood conditions and the boards needed to be replaced. In 1995, sampling again ended prematurely due to widespread flooding. Eight snake species were observed at MTC over the course of this study (Table 3). Whereas many individual snakes were recaptured within a year, no individuals were recaptured between years. The relationship between cumulative captures (excluding recaptures) and cumulative search time for the four most abundant snake species was linear for each pre flood year (e.g., Figure 4 for 1992). The sixteen correlation coefficients (four species, each with four years of collection) ranged from 0.87 to 0.99 with an average r = 0.95 (SD = 0.035). That there was no indication that the curves were leveling off for any species in any pre flood year indicates that there were many more snakes present in the population than we sampled and supports our decision to use captures per unit time as a comparative measure of snake abundance. Total snake abundance declined dramatically following the initial flood from 95 captures per 100 h to 30 captures per 100 h (Table 2). Using a paired samples test on the before and after values for each snake, the reduction in number of snakes was significant (Table 3; Wilcoxon Signed-Ranks test, T = 0, P = 0.01, n = 8). The difference between inter and post flood periods was not significant (Tables 2 and 3; T = 3, P 0.20, n = 6). By the end of the study, the Northern Watersnake (Nerodia sipedon) and Western Fox Snake returned to 79% and 81% of their initial abundances. The Black Rat Snake (E. obsoleta), Eastern Garter Snake (Thamnophis sirtalis), and Eastern Yellow-bellied Racer (Coluber constrictor), all relatively common initially, declined to 36%, 27%, and 25% of their initial abundances, respectively. Three species were essentially not observed after the 1993 flood (Table Volume 27 (2), 2007 Natural Areas Journal 137

6 Table 2. Sampling activity during the study of the effect of flooding upon the relative abundance of the snake fauna of the Marais Temps Claire Conservation Area St. Charles County Missouri USA. Total # Boards Examined Total # HoursSearc hed Total # Snakes Collected Year Flood Condition Starting-Ending Dates of Surveys Number of Visits 1990 Pre-flood 18 Apr - 26 Oct Pre-flood 2 Feb - 26 Oct Pre-flood 4 Feb - 25 Oct Pre-flood 7 Feb - 5Jul Total Pre-flood Inter-flood 14 Mar - 15Oct Inter-flood 18 Feb - 20 May Total Inter-flood Post-flood 11 May - 6 Jul Post-flood 27 Apr - 29 Sept Total Post-flood Total Table 3. Number of individuals captured beneath hide boards or caught by hand per 100 search hours for each of the eight species of colubrid snakes encountered at Marais Temps Claire Conservation Area. Values for the pre-flood sampling period are the mean and SE for the four years sampled. The two years represented in the inter and post flood periods are combined. Average annual count per 100 h (SE) Pre Flood Inter Flood Post Flood Species & & 2000 Coluber constrictor flaviventris Eastern Yellow-bellied Racer 8.5 (2.35) Elaphe obsoleta obsoleta Black Rat Snake 5.9 (1.34) E. vulpina vulpina Western Fox Snake 5.2 (0.30) ). Although the rarest two species were not seen again after the 1993 flood, there was no relationship between initial abundance (raw or log transformed) and percent decline in abundance following either the first or the second flood. Species diversity declined from pre flood to inter flood and post flood sampling (Shannon-Wiener H: 2.22, 2.08, 1.92, respectively) and species evenness increased slightly (Equitability E: 0.74, 0.80, 0.83, respectively). MTC biodiversity Total Snakes per 100 h Twenty-three snake species have been observed in St. Charles County (Johnson 2000). Three additional snake species are expected to be found in this county based on distribution maps of occurrence in adjoining counties. During the 11-year span of this study, we encountered only eight species, conservatively 35% of the source pool (not including the three snake species suspected but not directly observed in St. Charles Co.). We examined similar ratios from 11 other managed conservation sites within Missouri and Illinois (Table 4). The value S is taken as the number of species observed at the site and the value S is the number of species known to be present in the surrounding county and thus considered Nerodia rhombifer rhombifer Diamondback Watersnake 1.9 (0.90) 0 0 N. sipedon sipedon Northern Watersnake 13.1 (2.82) Regina grahamii Graham's Crayfish Snake 4.8 (1.92) 0 0 Thamnophis proximus proximus Western Ribbon Snake 8.0 (0.94) T. sirtalis sirtalis Eastern Garter Snake 54.7 (8.70) Natural Areas Journal Volume 27 (2), 2007

7 which explained 46% of the variation in snake presence at MTC. The arboreal trait explains an additional 10% of the variation. The size variable was not significant. Figure 4. Relationship between individuals observed and time spent sampling for the four most abundant snake species at Marais Temps Clair Conservation Area Correlation coefficients, r, are for T. sirtalis, for N. sipedon, for C. constrictor and for E. obsoleta. to represent a potential pool of immigrants to the conservation site. The ratio of S /S at the 11 other sites ranges from 0.40 to 0.89 (Table 4; mean = 0.713, SE = 0.046). When compared to these 11 sites in Missouri and Illinois, the MTC ratio (S 1 /S = 0.35) is significantly lower (one sample t-test, t = 2.41, df = 10, P = 0.037). Neither the number of species nor the fraction of source species represented at a refuge was explained by refuge size, large-scale habitat diversity, or tendency to flooding. However, refuges with upland habitats tended to have both a greater number of species and a higher fraction of source species represented. Characteristics associated with flooding We predicted that, in contrast to the overall snake fauna of St. Charles Co., proportionally more species at MTC would exhibit the following traits: semi-aquatic habits, semi-arboreal traits, and larger body size of adults. The values of these traits for snake species present at MTC and those present in the surrounding county but not at MTC were derived from Ernst and Barbour (1989) and Johnson (2000) and summarized in Table 5. To quantify aquatic and arboreal habits, a strong tendency toward aquatic or arboreal behavior (a yes in Table 5) was assigned a value of 3, some tendency (described in the literature as slight or possibly ) was assigned a value of 2, and no tendency was assigned a value 1. The eight MTC species exhibited a greater tendency toward being aquatic (average aquatic value 2.75 vs 1.53; t = 4.19, P < 0.001, df = 21) and of possessing arboreal habits (average arboreal value 2.75 vs 1.40; t = 4.24, P <0.001, df = 21) than the 15 non-resident species. Although the 1.21 m mean SVL of the MTC snake species was greater than the 0.84 m of the non-mtc species, the difference was not significant (t = 2.055, P = 0.053, df = 21). We looked at all three variables through stepwise regression to determine which combination of variables best explained the set of resident species at MTC. The trait that best predicted a species presence at MTC is aquatic habit, We predicted that within the MTC populations of snakes, larger individuals would be more likely to survive flooding or recolonize a flooded habitat than would smaller conspecific individuals. We examined the average size of snakes captured before and after the two flooding events. We were hampered by the fact that very few snakes were captured after the initial flooding event, and none were recaptured from this earlier time period. We considered males and females of each species separately and used only species for which more than one individual was captured after the 1993 flood. In general, snakes captured after the 1993 flood were of a size that would have placed them above the median size of the pre-flood population (Table 6). Of the 31 snakes captured after the 1993 flood, 22 (71%) were above pre-flood median size for their gender and species, significantly more than expected by chance (chi square = 5.45, df = 1, P = 0.020). DISCUSSION Flooding reduced populations of five snake species by nearly 70% and either eliminated the populations of the other three species or reduced them to levels not detectable by our sampling. Two of the rarest species in our pre-flood sampling, Nerodia rhombifer and Regina grahamii, were not observed after the first flood despite nearly 200 hours of searching, reinforcing the general concern for the persistence of rare species in isolated habitats, especially those subject to periodic disturbance. The snake community, even before the floods, contained only a small fraction of the species known to occur in St. Charles County (Johnson 2000). This fraction was significantly lower than those of other conserved areas (Table 4). At least nine species of snakes absent from MTC but present in St. Charles County (Johnson 2000) occupy habitat types that do exist at MTC as described by Ernst and Barbour (1989) (Table 5). Only one of these missing Volume 27 (2), 2007 Natural Areas Journal 139

8 Table 4. Fraction of species of snakes (S ) known to occur in various wildlife refuges in Missouri and nearby Illinois in the U.S.A. compared to the number of species ( S ) in surrounding or adjoining counties. County data for Missouri (MO) are from Johnson (2000) and for Illinois (IL) from Phillips, Brandon & Moll (1999). Site Size (ha) Habitat Flood Prone S S S /S Source Cuivre River, Lincoln Co., MO 2587 mostly uplands no B. Schutte (personal comm. 10 Jan. 2006) Mingo, Stoddard Co., MO Pine Hills, Union Co., IL Ashland, Boone Co., MO Tyson Research Center, St. Louis Co., MO Sandy Ridge, Jefferson Co., MO Ted Shanks Conservation Area, Pike Co., MO Squaw Creek National Wild-life Refuge, Holt Co., MO Spunky Bottom, Brown Co., IL Kaskaskia, Clinton Co., IL Union Ridge, Sullivan Co., MO Marais Temps Clair, St. Charles Co., MO species, Nerodia erythrogaster, would be expected to be present based on its combination of size and aquatic and arboreal tendencies. While it is described as living along the Mississippi River floodplain, MTC is close to the northern boundary for this species (Gibbons and Dorcas 2004). With limited and disjunct populations to the north, recovery from flooding events for this species may be unlikely. In contrast, 8772 Bottomland wetlands, some upland forest ~1000 mixed lowland, upland minor Anonymous (undated) in parts Rossman (1959) 923 Upland no Clauson & Baskett (1982) 796 upland forest and fields 7.5 forest and xeric glade minor Sexton (personal observation) no Sexton (1982) 2685 Lowland wetlands in parts Jones & Shulse (1995) 2974 Mainly wetlands, some upland yes Bell (2005) 486 fields and wetland no Tucker & Phillips (unpubl. data) ~8000 flood plain, forest seminatural flooding 3304 forest, grass, old fields 371 Wetlands, croplands the western fox snake was found at MTC despite being neither arboreal nor strongly aquatic. Its persistence at MTC may in part be accounted for by the preserve being at the southern end of its distribution, with drift from flooding events from the north serving to bring individuals into the preserve. We can also hypothesize that its relatively large size may allow it to direct its movement from rising floodwaters Wilson (2000) no Kangas & Harford (1997) yes This study However, why this species should persist at MTC, and recover reasonably well from the 1993 and 1995 floods, while other species with similar characteristics do not, is not answered by this study. The 1993 flood onto a farm drove individuals of several species not observed at MTC 1100 m upstream of MTC. The Ehmler house and yard were on a knoll 140 Natural Areas Journal Volume 27 (2), 2007

9 Table 5. Comparison of traits of species present at Marais Temps Clair Conservation Area with those known to occur in St. Charles County (Johnson, 2000) but not observed at MTC. Characteristics from Johnson (2000) and Ernst and Barbour (1989). Maximum Length Maximum Length Species Arboreal Aquatic (m) MO (m) US Species observed at Marais Temps Clair Coluber constrictor Yes Slight Elaphe obsoleta Yes Yes E. vulpina No Slight Nerodia rhombifer Yes Yes N. sipedon Yes Yes Regina grahamii Yes Yes Thamnophis proximus Yes Yes T. sirtalis Yes Yes Species known to occur in St. Charles County, but not observed at MTC. Stars (*) indicate species with suitable habitat at MTC, Agkistrodon contortrix No No Carphophis vermis No No Diadophis punctatus No No Heterodon platirhinos * No No Lampropeltis calligaster * No No L. getulus No Possibly L. triangulum * No No Nerodia erythrogaster * Yes Yes Opheodrys aestivus * Yes No Pituophis catenifer * Slight No Sistrurus catenatus No Yes Storeria dekayi * No Slight S. occipitomaculata * Slight Slight Thamnophis radix * No Slight Virginia valeriae No No 0.25 Species inferred to be in St. Charles County, not observed at MTC (not included in analysis) Elaphe guttata No No Tropidoclonion lineatum No No Crotalus horridus Slight No about 1.5 m above maximal flood level and were surrounded by water. Mr. Ehmler informed us that his family had occupied that farmstead for 100 years and that it had never been subject to such high flooding. In 1993, he removed approximately 200 garter snakes (Thamnophis spp). In 1994, we visited the farm four times and removed 30 Thamnophis sirtalis, 23 T. radix, one Storeria dekayi, and one Lampropeltis calligaster. The latter three species have not been observed during this study at MTC despite the presence of suitable habitat. The combined diversity of snakes at MTC and the Ehmler farm (11 species) approaches that of another riverine refuge, the Squaw Creek National Wildlife Refuge in northwestern Missouri (15 species including the 11 identified above). Much of this refuge was also flooded by the Missouri River in 1993; but, unlike MTC, Squaw Creek is bordered by upland loess bluff hills, which may act as a refuge during flooding events, allowing for a higher diversity. We present two explanations for the lack of diversity of snake species at MTC. The first Volume 27 (2), 2007 Natural Areas Journal 141

10 Table 6. Comparison of SVL (cm) for snakes captured before and after the first flooding episode by species and gender for those species present after the first flood. Median values provided for two or more captures. Species Gender Pre-flood Median SVL (# individuals) Post-flood Median SVL (# individuals) percent of inter- and post-flood captures above pre-flood median SVL Thamnophis sirtalis Male 49 (65) 52 (5) 80.00% Female 62 (140) 67.8 (14) 71.40% Elaphe vulpina Male 76 (10) (0) Female 82.5 (8) 82 (2) 50.00% Coluber constrictor Male 76 (18) 90 (3) % Female 81 (8) (1) Elaphe obsoleta Male 126 (15) 116 (3) 33.00% Female 114 (10) 123 (3) % is the negative impact of frequent flooding exacerbated by changes in the river dynamics caused by human interference with the natural riverine cycle (Galat et al. 1998). The second is another flood, that of Euro- American settlers who changed the presettlement landscape beginning with the settlement of St. Charles in 1769 (Figure 1). Schrott et al. (2005) recently proposed that local extinction risks depend not only on the current state of the landscape but also on the history of the past disturbances. Here, we briefly review the history of landscape changes following settlement that established physical barriers such as roads, agricultural fields, settlements, etc., that restricted or eliminated movement of animals such as snakes within the Point. In 1804, Captain William Clark, before the ascension of the Missouri River, visited the Point and described the extent of the prairie and the activities of the residents of Portage des Sioux in raising corn and wheat thereon (Mincke 1999). Stoddard (1812) described the extent of the prairie and stated that the settlers lived in the nearby hills, not on the prairie. A land survey of of the area frequently mentioned topographic features such as bodies of water and types of prairies (United States Land Survey ) but made no mention of Euro- American artifacts. In 1826, Duden (1980) wrote that the prairies were still largely uninhabited and that the settlers lived in the adjoining hills. A second land survey of 1855 (United States Land Survey 1855) that covered the same area as the previous one clearly indicated the extent of Euro- American settlement by mentioning the presence of houses, orchards, agricultural fields, and roads. In 1865, much of the area was still in prairie, but by 1885 corn, wheat, and meadows had taken over and orchards were abundant (one planted with 10,000 trees (Anonymous 1885)). Based on such historic documentation, we infer that immigration of the more terrestrial species of snakes from upstream sources to MTC was limited as early as The rapid settlement of this region and the resultant land management practices would have affected the snake community by: (1) reducing or eliminating habitats which might have served as corridors (sensu, Rosenberg et al. 1997), particularly for the more terrestrial species of snakes, between potential upstream, upland sources of immigrants and MTC; (2) modifying the habitat of MTC (Rood et al. 2005); (3) reducing or eliminating the availability of sites which might serve as temporary refuges in times of flooding for resident populations at MTC; and (4) increasing the frequency and extent of flooding events (Galat et al. 1998; Rood et al. 2005). Although the 1993 and 1995 floods were among the most severe in recorded time, flooding of both rivers is relatively frequent. For example, river levels on the Mississippi River at St. Louis attained or surpassed minimal flood levels 58 times between 1861 and 2006 (NOAA 2006). Major floods, those that exceeded flood stage by 3 m, occurred five times during this same 145-year period. All five of these major floods occurred in the past 60 years, three of them in the past 35 years. The 1993 flood was the largest on record, nearly 6 m above flood stage. As the frequency of major floods increases, the likelihood that a major flood will occur within the recovery period of an earlier flood increases and may thus further impede recovery of wildlife populations. Protected but isolated conservation areas like MTC, which are subject to major environmental disturbance, may require additional management practices to help preserve their fragile biodiversity (Galat et al. 1998; Michener and Hauber 1998; Rood et al. 2005). We propose that one or more islets that rise higher than periodic flood levels be constructed within or at the periphery of the refuge. They would be modeled on the Ehmler farm, which served as an island refugium for survivors of the 1993 flood and as a potential dispersal point for invasion of new terrain. The area above flood level at the Ehmler farm was not large (1 ha) and it did not provide native habitat, but it did contain 142 Natural Areas Journal Volume 27 (2), 2007

11 crevices along the foundations of buildings, and farm artifacts provided considerable structural diversity that likely provided refuge from both floodwater and predators during flooding events. Stable, but structurally complex habitat above highest flood stage appears to be important design elements. Other criteria (size, shape, vegetation, etc.) would follow that of natural islands in rivers and other characteristics of undisturbed local sites. Such constructed refugia would serve two purposes: (1) to act as a lifeboat that would serve as temporary shelter for resident species until the floods receded and (2) to act as a landfall for individuals of both resident and non-resident species swept down from upstream locations. The lifeboat effect would serve to reduce the loss in population size of resident species (and of genetic diversity) with the result that population size could increase more rapidly after the cessation of flooding. The landfall effect could enhance the biodiversity of the refuge by utilizing the flood waters as a corridor between upstream sources and downstream sinks (Pulliam 1988; Dubois and Stoll 1995; Haddad et al. 2003), introducing individuals of novel species and/or of novel genotypes of resident species from upstream. ACKNOWLEDGMENTS Over the course of 12 seasons, we became indebted to a large number of sources of support and information. The Missouri Department of Conservation generously gave us access to Marais Temps Clair, permission to use a map to illustrate the layout of our study area, and financial support. The field personnel at Marais Temps Clair were always helping us on our mission. Student volunteers from the Department of Biology, Washington University, and former and current students at Fox High School, Jefferson County, Missouri, helped with the fieldwork. The latter included: Eric Compas, James Evans, Teddy Gray, Eddie Mosier, Scott Strattow, Paul Touchette, and Dan Trofholz. The Ehmler family graciously provided access to their property. Personnel of the St. Charles County Historical Society, particularly Ms. Carolyn Roth, provided voluminous references to the history of Portage des Sioux Township. Ms. Colleen Schaper and Mr. Donald Mincke, two private historians of St. Charles County, opened their personal archives to us. Ms. Ida Gerdiman, Historian for the Boone- Duden Historical Society, permitted us to reproduce the map of 1875 from an atlas owned by the Society. This manuscript benefited from comments by Dr. Jon Chase and two anonymous reviewers. Ms. Joyce Duncan typed the manuscript. To all of these individuals and organizations, we are most indebted. Owen J. Sexton is Emeritus Professor, Washington University Department of Biology, and former Director of Washington University s Tyson Research Center. His research interests include reptilian ecology, behavior and physiology, and tropical biology. Wayne J. Drda is Emeritus Faculty, Fox C-6 School District in Jefferson County, Missouri. He is the Field Research Manager of the Rattlesnake Project at Washington University s Tyson Research Station. Kenneth G. Sexton is a herpetologist and field assistant at Washington University s Tyson Research Station. Judith Bramble is an Associate Professor in the Environmental Science Program at DePaul University in Chicago, Illinois. Her research interests are in urban and restoration ecology. LITERATURE CITED Anonymous History of St. Charles County, Missouri ( ). Reprinted with introduction by P.R. Hollrah Patria Publishing, Tulsa, Okla. Anonymous. Undated. Reptiles and Amphibians of Mingo National Wildlife Refuge. U.S. Fish and Wildlife Service. Available online < Accessed 10 January Bell, R Squaw Creek National Wildlife Refuge Comprehensive Conservation Plan. U.S. Fish and Wildlife Service. 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