estimated number of snake species that can be managed by species survival plans in north america

Zoo Biology 12:243-255 (1 993)

RESEARCH ARTICLES

Estimated Number of Snake Species That Can Be Managed by Species Survival Plans in North America Hugh Quinn and Holly Quinn

Topeka Zoological Park, Topeka, Kansas

A survey designed to estimate the number of snake enclosures available for Species Survival Plan (SSP) programs was distributed to all North American zoos containing 100 or more reptile and amphibian specimens. Of the 52 zoos surveyed, 44 (84.6%) responded, indicating that 790 (26.3%) of the 3,012 snake enclosures were available for SSP programs. Available enclosures were classified by size and existing themes to help define limitations of the potential SSP space. This spatial information was then used in conjunction with existing population genetics models to estimate that up to 16 snake species can be accommodated by SSP programs in these zoos collectively. Values used in the models were estimates of those for an average snake species with a generation time of 15 years, lambda of 1.15, with 26 effective founders, and an n,/n ratio of 0.3. It was further assumed that 90% of the genetic variation would be maintained in each species for a period of 100 years. Tactics to increase the number of species that SSP programs can accommodate include: increase reserve space, devote more space for SSP snakes, lengthen generation time, promote gene exchange with wild populations, goal SSP programs for less than 200 years, invest in short-term programs, involve the private sector, build new enclosures, increase the number of snakes per enclosure, and encourage participation of non-North American institutions. To maximize biological diversity in relation to captive carrying capacity, it is recommended that SSP programs represent both infraorders of living snakes and as many families within those infraorders as possible. Although not all 16 families of snakes are likely to be represented due to exhibit value, obtainability, and husbandry success, it may be possible to represent as many as nine families in 16 SSP programs. 0 1993 Wiley-Liss, Inc

Key words: snake, SSP, captive carrying capacity, collection planning

Received for publication August 30, 1992; revision accepted January 18, 1993.

Address reprint requests to Hugh Quinn, Topeka Zoological Park, 635 Gage Boulevard, Topeka, KS 66606.

0 1993 Wiley-Liss, Inc.

244 Quinn and Quinn

INTRODUCTION

Many species of snakes are known to be threatened with extinction or to be experiencing declining populations [Dodd, 19871. Due to the secretive nature of most snakes, population estimates are often difficult to secure and it may be that populations of additional species are declining undetected. One means of conserving snake species is through captive propagation. In 1981, the American Association of Zoo- logical Parks and Aquariums (AAZPA) developed the Species Survival Plan (SSP) to coordinate captive breeding programs among North American member institutions. Generally, SSP programs strive to preserve 90% of the genetic variation (measured as average heterozygosity) for a given species for 200 years [Foose et al., 1986; Soule et al., 19861. More recently, it has been suggested that program duration be set at 100 years [Foose and Seal, 19911. However, the 100-year duration should not be a set standard. Every species has different conservation program needs, and the length of time required for successful programs is dependent on too many variables to set a standardized program duration for all species.

Meeting the genetic goals of SSP programs often requires a substantial number of individual animals, and thus a substantial amount of enclosure space. Such space is limited in zoos, and thus the number of species that zoos can accommodate through their SSP programs is limited [Hutchins and Wiese, 1991; Soule et al., 19861. At this time, SSPs exist for only three snake species: the Dumeril’s ground boa, the Aruba Island rattlesnake, and the Virgin Island boa. This study estimates the number of snake species that SSP programs can accommodate, based on the number of enclosures currently available for such programs.

MATERIALS AND METHODS

To estimate the number of snake enclosures available in zoos for Species Sur- vival Plan (SSP) programs, a survey was sent to all zoos listed as maintaining >lo0 reptile and amphibian specimens [Boyd, 19901. Simply asking “how much space” zoos currently devote to snakes will not provide accurate information on how SSPs can utilize this space. For example, the Houston Zoo has -50 snake enclosures, but they are organized to display snakes from each of four different biomes or habitats. A certain number of enclosures are dedicated to snakes from each habitat. Further, the enclosures within these habitats are of various sizes, and will accommodate only appropriately sized snakes. At Houston, therefore, the number of snakes that can be accommodated for SSP purposes is a function of snake habitat and size. Since many zoos organize their snake enclosures according to some thematic approach and have enclosures of various sizes, these variables must be considered in determining the number of available enclosures for SSP programs. The number of occupied snake enclosures that zoos are willing to devote to conservation programs and designated SSP species is another factor to consider in determining SSP snake carrying capacity.

To assess potential SSP participation, therefore, the survey requested classification of these available enclosures into designated themes (if any) and sizes (Table 1). It further requested information regarding the number of enclosures, reserve (off-exhibit) and exhibit, currently occupied by snakes (Table 2), and the number of these enclosures participating zoos were willing to make available for existing and future SSP species (Table 3).

Snake Captive Carrying Capacity in Zoos 245

TABLE 1. Enclosure size classes for snakes of given lengths

Adult snake length Enclosure length Enclosure width Enclosure floor area

0.61 0.61 0.31 0.19 1.22 1.22 0.61 0.74 1.83 1.83 0.92 1.68 3.05 3.05 1.53 4.67 4.58 4.58 2.14 9.80

(m) (m) (m) (m2)

Enclosure size classes (Table 1) were derived by considering size classes of snakes that would fit into such enclosures. Determinations were made by examining various sizes of snakes in various sizes of enclosures. It was estimated that an enclosure should have one floor dimension equal to the length of its resident snake so the animal could fully extend its body, and the other floor dimension half that value. It was also considered that such an enclosure would be of sufficient size to house a pair of these snakes. Enclosure height was not considered, as most enclosures are of sufficient height to accommodate any snake species. Snake size classes were chosen somewhat arbitrarily and represented adult lengths.

Number of snakes needed to meet SSP genetic goals were calculated using the computer software CAPACITY [Ballou, 19891. General estimates of these values were entered into the program for these calculations since the variables utilized in this software will have different values from species to species, and all values are not actually known for any snake species. However, values of lambda 1.15 and n$n 0.3 are actual figures for existing SSP populations of Dumeril’s ground boas and Aruba Island rattlesnakes (R.A. Odum and J. McLain, personal communication) and were applied to all snake species for these calculations. Other values are: generation time 15 years; program duration 100 years; genetic variation retained 90%; and number of founders 26. This information is presented in Table 4B, and a discussion of why these values were selected is presented below.

RESULTS

With a limited amount of captive space for SSP species, it is important to decrease the number of enclosures required to maintain any one species in order to increase the number of species that could be accommodated by SSP programs. This can be accomplished in several ways. First, it will be necessary to extend the generation time of each species as long as possible. Table 4A,B illustrates this by comparing the number of enclosures required to maintain one species for generation times of 10 and 15 years. By increasing the generation time by 5 years, the number of enclosures required to house these snakes is reduced by - one-half because fewer snakes are necessary to maintain genetic variation. (For the calculations in this study, a generation time of 15 years was arbitrarily chosen, as it seemed a reasonable estimate for an average of all snakes. It probably represents too long a generation time for smaller snakes, yet potentially too short a generation time for many of the larger snakes.) Second, limiting the program duration from 200 to 100 years reduces the number of enclosures required by more than one-half (assuming all other variables are held constant) because fewer snakes are required over time. Originally, SSP programs

246 Quinn and Quinn

TABLE 2. Survey summary of snake carrying capacity in zoos*

Number of enclosures Enclosure size Reserve Exhibit Total % Devoted

Category (m2) All (SSP) All (SSP) All (SSP) to SSP

No theme

Desert

Grassland

Temperate forest

Tropical forest

Cloud forest

Montane

Africa

Asia

North America

South America

Australia (New Guinea)

Asia and Australia

0.19 0.74 1.68 4.67 9.80

0.19 0.74 1.68

0.19 0.74 1.68

0.19 0.74 1.68 4.67 9.80

0.19 0.74 1.68 4.67 9.80

0.19 0.74 1.68 4.67

0.74

0.19 0.74 4.67

0.19 0.74 1.68

0.19 0.74 1.68 4.67 9.80

0.19 0.74 1.68 4.67

0.19 0.74

0.74 1.68 4.67

20.1 23.8 25.7 22.5 66.7

57.0 51.2 85.7

96.7 83.3

100.0

48.9 65.4 80.0

100.0 0.0

51.2 34.1 50.0 33.3 20.0

100.0 75.0 50.0 0.0

50.0

44.4 25.0 50.0

50.0 100.0

0.0

11.7 19.4 25.0 0.0 0.0

23.1 25.0 50.0

100.0

33.3 22.2

33.3 0.0 0.0

(continued)


TABLE 2. Survey summary of snake carrying capacity in ZOOS* (continued)

Number of enclosures Enclosure size Reserve Exhibit Total % Devoted

Category (m2) All (SSP) All (SSP) All (SSP) to SSP Indo-Malay sia

Boas and Pythons

Colubrids

Crotalids and Viperids

Elapids

Rear-fanged

Harmless

Arboreal

Terrestrial

Aquatic

Cool room

1.68 9.80

0.19 0.74 1.68 4.67 9.80

0.19 0.74 1.68

0.19 0.74 1.68 4.67

0.19 1.68 4.67

0.19

0.19 0.74 1.68

0.19 0.74 9.80

0.19 0.74 I .68 9.80

0.19 0.74

0.19 0.74 1.68

50.0 100.0

27.3 14.3 50.0 40.0 25.0

20.0 0.0 0.0

12.7 0.0

10.0 0.0

0.0 25.0 0.0

100.0

24.2 0.0 0.0

50.0 44.4 25 .O

30.8 53.9

100.0 100.0

100.0 100.0

56.8 33.3 0.0

*Figures indicate number of snake enclosures in zoos. Figures in parentheses indicate enclosures available for SSP programs. Missing enclosure sizes within categories indicate no enclosures of those sizes were reported.

were designed to conserve 90% of a species’ genetic variation for 200 years [Foose et al., 1986; Soule et al., 19861. However, recent considerations of program duration have revised that figure to 100 years [Foose and Seal, 19911; a shorter program duration provides opportunities for inclusion of additional taxa in captive programs and “buys time” for those that might otherwise become extinct. As discussed earlier, the 100-year program duration should not be a set standard. However, for purposes of calculations here, a 100-year program duration was used. Third, increasing the

248 Quinn and Quinn

TABLE 3. Number of snake enclosures (reserve and exhibit) available for SSP programs*

Enclosure size (m2)

Category 0.19 0.74 1.68 4.67 9.80 Total

No theme 328 81 35 11 4 459 Desert 45 21 6 0 0 72 Trop. forest 22 14 8 1 1 46 Temp. forest 22 17 4 1 0 44 Grassland 29 5 1 0 0 35 Cool room 25 1 0 0 0 26 North America 9 6 2 0 0 17 Terrestial 4 7 1 0 1 13 South America 3 4 3 1 0 11 Boids 3 1 3 2 1 10 Viperidae 9 0 1 0 0 10 Harmless 10 0 0 0 0 10 Cloud forest 3 3 1 0 0 7 Arboreal 2 4 0 0 1 7 Africa 4 1 0 1 0 6 Asia 4 1 0 0 0 5 Australia 1 2 0 0 0 3 Asia and Australia 0 2 0 0 0 2

Montane 0 1 0 0 0 1

Colubrids 1 0 0 0 0 1

Aquatic 1 1 0 0 0 2

Indo-Malaysia 0 0 1 0 0 1

Elapids 0 0 1 0 0 1 Rear-fanged 1 0 0 0 0 1 Total 526 172 67 17 8 790

*Total number of enclosures per category/theme are listed in descending order.

number of founder snakes decreases the number of snakes and required enclosures to maintain one SSP species (Table 4A,B).

If all life table criteria as outlined in Table 4B are met, then 26 founders would optimize the limited enclosure space to accommodate the maximum number of species possible in meeting SSP goals. Addition of more founders would not be bene- ficial to the program unless a substantial number were added. Thus, if we accept that the life table data presented in Table 4B are representative of that for an average snake species, SSPs should strive to meet these guidelines with 26 founders and a program duration of 100 years. With this scenario, 49 enclosures with two snakes per enclosure would be required to maintain each SSP species.

Of the 52 zoos surveyed, 44 (84.6%) responded, indicating that 790 (26.3%) of the 3,012 existing snake enclosures, both reserve and exhibit, were available for SSP programs (Tables 2, 3). Although not used in our calculations, additional enclosures were probably available in those nonresponding and nonsurveyed institutions. There- fore, our estimate of available SSP space should be considered conservative. Snake enclosures in responding zoos were arranged in 24 different themes, including Cool Room (a designated area where animals are generally maintained at 20-25°C) and No Theme (the absence of an overall theme). The largest theme category among respon- dents was No Theme, with 459 enclosures available for SSP use. Following the No Theme category in number of existing or potential SSP enclosures were the habitat


TABLE 4. Carrying capacity required to maintain 90% of the original heterozygosity for various time periods given various founder numbers where lambda is 1.15, n,/n is 0.3, and generation time is 10 years (A) and 15 years (B)*

No. of effective 100-year program: 200-year program: founders No. of enclosures No. of enclosures

A. Generation time = 10 years 10 320 (160) 15 213 (107) 20 187 (94) 25 177 (89)

26 171 (89) 27 173 (87) 28 173 (87) 29 170 (85)

30 170 (85) 35 167 (84) 40 163 (82)

B: Generation time = 15 years

10 157 (79) 15 117 (59) 20 107 (54) 25 100 (50)

26 97 (49) 27 97 (49) 28 97 (49) 29 97 (49)

30 97 (49) 35 97 (49) 40 97 (49)

737 (369) 477 (239) 407 (204) 373 (187) 370 (185) 367 (183) 363 (182) 360 (180) 360 (1 80) 350 (175) 343 (171)

383 (192) 280 (140) 250 (125) 237 (119) 233 (117) 230 (115) 230 (115) 227 (114) 227 (114) 220 (110) 217 (109)

*Figures indicate the number of enclosures required with one snake per enclosure, and in parentheses, with two snakes per enclosure.

themes of Desert (72 enclosures), Tropical Forest (46 enclosures), Temperate Forest (44 enclosures), and Grassland (35 enclosures). With the exception of Cool Room (26 enclosures), all other themes contained < 20 enclosures for SSP purposes.

If the theme of the enclosure (Tables 2, 3) is the restricting variable in accom- modating SSP species, and 49 enclosures are required per species, then only two themes-No Theme and Desert-have a sufficient number of enclosures. No Theme could accommodate a little over nine species, and Desert could accommodate between one and two species. Note that enclosure size was not considered in these calculations. Tropical Forest and Temperate Forest could each accommodate slightly less than one species each. The other themes do not individually provide sufficient space to accommodate a single species. Allocating nine species to No Theme, two species to Desert, and optimistically including one species each for Tropical Forest and Temperate Forest, the data indicate that 13 species could be accommodated with SSP programs.

Because a large number of enclosures is needed for each SSP species, it appears that N o Theme is the least restrictive and, therefore, the most advantageous approach to maintaining snakes for SSP purposes. If a species is confined to a particular theme that does not have enough enclosures to support an SSP program, or if a particular

250 Quinn and Quinn

theme does not include any chosen SSP species, then the enclosures with that theme may not be useable for SSP programs. However, No Theme presumably means “any theme,” which suggests that these enclosures could increase the number of enclosures for other themes. Therefore, categories with <49 allocated spaces may not be problematic. In contrast, a single species may span several themes, thus increasing the number of SSP enclosures available for it. For example, if the SSP species is a terrestrial python from the tropical forests of Australia, then enclosures with themes including Tropical Forest, Australia, Asia and Australia, Boids, Harmless (nonven- omous), Terrestrial, and No Theme (Table 3 ) may be available for that species.

Considering enclosure size as well, however, suggests that the above estimation of 13 SSP species may be optimistic; only the No Theme category has enough enclosures of any given size class to accommodate one or more species (Table 2). No Theme could accommodate about seven species in small enclosures (0.19 m2), and nearly two in slightly larger enclosures (0.74 m2). The Desert theme could accommodate one species in small enclosures (0.19 m2). Unless we can cross theme or enclosure size boundaries with certain snake species, it appears that we can only accommodate -10 species, and that they must be relatively small snakes. Consid- ering both enclosure theme and size is, therefore, the most restrictive approach to determining available space for snake SSP species.

Enclosure size alone may prove somewhat restrictive in determining which snake species are chosen for SSP programs rather than how many snake species are chosen, unless there is a preponderance of giant snake SSP species. Whereas small snakes could conceivably be maintained in enclosures designed for giant snakes, the reverse is not feasible. Therefore, if enclosure size is the determining factor in SSP program viability (Table 3 ) , then we must consider the size of the snake species destined for those enclosures. Of the 790 enclosures available for SSP programs, >66% of them are relatively small: 526 enclosures have floor dimensions of -0.19 m2, 172 enclosures have floor dimensions of 0.74 m2, and 67 have floor dimensions of 1.68 m2 (Table 3 ) . The 765 small enclosures (up to 1.68 m2 in floor dimensions) can collectively accommodate 15 species of small snakes using the 15-year generation time. The number of species accommodated will fluctuate somewhat, based on the size of individual snake species and their appropriateness to these small enclosures.

For giant snakes such as Python reticulum, P . molurus, P . sebae, or Eunectes rnurinus, however, there are only 25 enclosures (17 enclosures with floor dimensions of 4.67 m2 and eight enclosures measuring 9.80 m2). Although it was determined earlier that 49 enclosures were required to maintain one snake SSP species, giant snakes generally have longer generation times than small snakes, and thus require fewer enclosures for long-term maintenance. By increasing the generation time for these species, we attempted to increase the number of giant snake species that can be accommodated by SSP programs in these 25 enclosures. If we strive for a generation time of 26 years or more, we can limit a species to only 15.7 enclosures, but with three snakes instead of two per enclosure. However, this generation time is unreal- istic. Decreasing generation time to the 21-25-year range requires 21 enclosures per species, again with three snakes in each enclosure. Further decreasing generation time to a more realistic 17 years, we would require 26.7 enclosures containing three snakes each. Therefore, with 25 available enclosures, it appears we have space to conduct only one SSP for a giant snake species.

Unlike enclosure size, theme does not restrict the choice of a giant snake species


to a great extent, as 15 of the large enclosures are No Theme (Table 3), two are Tropical Forest (where many of the giant snakes reside), and three are Boids (which could include all giant snakes). Most of the 25 enclosures should be available for any species of giant snake chosen; the only enclosures with themes that may affect species selection are Terrestrial, Arboreal, South America, Africa, and Temperate Forest, each with one giant snake enclosure.

If neither theme nor enclosure size is considered in the calculations of the number of snake species that can be accommodated by SSP programs, and the assumptions in Table 4B for 100 years with 26 founders are met, then 16 species could be accommodated. This figure is derived by grouping all themes and enclosure sizes, including those that do not individually provide sufficient space to maintain a single SSP species. In other words, 790 enclosures, with 49 enclosures allocated per species, would accommodate 16 species of snakes in SSP programs.

It is important to note that both reserve and exhibit enclosures are included in the total number of enclosures calculated for SSP purposes. However, unless a zoo participating in an SSP program for a designated snake species wishes to display the same species in several enclosures, it will be required to use reserve enclosures for maintaining additional specimens. Reserve space, therefore, is an important component in establishing and conducting an SSP program.

Again, the above discussion is based on species that meet all the life table assumptions outlined in Table 4B for 100 years with at least 26 founders. Keep in mind that values used in the calculations were described to represent an average of all snake species. If any of these variables are altered, the results will also be altered. For example, decreasing the number of founders, increasing the duration of the program, or decreasing the generation time will reduce the number of species that can be accommodated with SSP programs. The lambda and n,/n values are actual figures for existing SSP populations of Dumeril’s ground boas and Aruba Island rattlesnakes, and may or may not be applicable to other species. As individual species are chosen, more accurate estimates of these values can be made. It is assumed that some SSP species chosen will have higher values than those chosen, and some will have lower values.

DISCUSSION

Following are a few ways to increase the number of snake species that SSP programs can accommodate.

Increase reserve space. As discussed earlier, reserve space is an important component in allocating a sufficient number of enclosures for any snake SSP species. Many zoos have reserve space that is not utilized to its fullest extent. Utilizing all available space will help expand the number of enclosures available for SSP programs. When new reptile facilities are built, creating large reserve areas should be encouraged. This is a relatively inexpensive way that zoos and aquariums can expand their conservation commitments.

Devote more space for SSP snakes. As mentioned above, zoos responding to the survey are willing to commit only 26.3% of existing snake enclosures for SSP use. By increasing this commitment, the number of species that can be accommodated by SSP programs can also be increased. At the same time, more enclosures will probably become available as SSP programs increase in number and diversity. This

252 Quinn and Quinn

may occur as species are identified as high priority by the AAZPA’s Snake Taxon Advisory Group.

Lengthen generation time. Both delaying breeding as long as possible during the life of a snake, and genome banking are ways to lengthen the generation time of snake species. Lengthening the generation time will decrease the number of specimens needed to meet defined genetic goals, decrease the amount of enclosures required by a single species, and will thereby increase the number of species that SSP programs can accommodate overall within the limited number of enclosures available. Genome banking can extend generation time and can also play an important role in facilitating gene exchange between captive and wild populations. A substantial amount of work is needed in the field of genome banking for snakes. No embryos or gametes have been successfully stored, and successful artificial insemination has been accomplished only once [Quinn et al., 19891.

Promote gene exchange with wild populations. Introducing genes from the wild population into the captive population effectively increases the number of founders. This, in turn, decreases the number of animals needed to meet defined genetic goals, and thus increases the number of species that SSP programs can accommodate within the limited number of enclosures available.

Goal SSP programs for < 200 years. As discussed above, many more species can be accommodated in SSP programs that are 100 years in duration rather than 200 years. A shorter program provides opportunities for inclusion of additional taxa in captive programs and “buys time” for those that might otherwise become extinct.

Invest in short-term programs. Some programs may have the potential to quickly re-establish stable wild populations. When this occurs, new species can be chosen to occupy the spaces of the “saved” species. In this way, more species can benefit from the SSP programs.

Involve the private sector. Many highly competent herpetoculturists who have an intense interest in conservation are found in the private sector. By involving these people in our SSP programs, both the number of SSP enclosures and the number of snake species accommodated by these programs can be increased. This is especially true for giant snake species. Private sector participants must be willing to adopt SSP ethical and husbandry standards, and to share information vital to the success of the SSP.

Build new enclosures. Encourage construction of more reptile facilities in zoos and aquariums. Also, examine facilities that currently do not contain snakes, and encourage curators to include these animals.

Increase the number of snakes per enclosure. By increasing the number of snakes per enclosure, fewer enclosures will be needed per SSP snake species. This will increase the number of species that can be accommodated by SSP programs. However, care should be taken to avoid unwanted breedings and unknown parentage.

Encourage participation of non-North American institutions. There are probably several institutions in Latin America, with no such programs in their countries, that would be interested in participating in SSP programs. This would increase the number of enclosures available for SSP programs, and thereby increase the number of species that could be accommodated. Collaborative programs with SSP- like conservation efforts in other countries will also allow expansion of SSP programs.

It is clear that up to 16 snake species can be accommodated by SSP programs.


TABLE 5. Classification of living snakes*

Infraorder Scolecophidia Family Anomalepididae Family Typhlopidae Family Leptotyphlopidae

Infraorder Alethinophidia Superfamily Acrochordoidea

Family Acrochordidae Superfamily Anilioidea

Family Loxocemidae Family Xenopeltidae Family Aniliidae Family Uropeltidae

Superfamily Tropidopheoidea Family Tropidopheidae

Superfamily Bolyerioidea Family Bolyeriidae

Superfamily Booidea Family Pythonidae Family Boidae

Superfamily Colubroidea Series Proteroglypha Family Atractaspididae Family Elapidae

Series Opisthoglypha Family Colubridae Family Viperidae

*McDowell [1987].

Creative thoughts, concentrated efforts, and coordination need to be directed toward increasing this number. However, it is also clear that the species chosen for SSP programs must be considered carefully. If those species are to represent the diversity of snakes worldwide, a pro-active approach must be taken in defining which species will be the focus of SSP programs. The “old” method of defining species was to wait until a species was proposed, then react as to whether or not its SSP inclusion was justified. This approach will not guarantee a representative sample of the diversity of snake life to be preserved over time. A more reasonable approach is to examine species within all snake higher taxonomic levels (families), which is similar to the approach taken by Diebold and Hutchins [1991] for birds. SSP criteria could be applied to each family of snakes until a species or several species were identified as suitable SSP candidates. Once this is complete, a list of one or more species from each family would be available for evaluation.

If we consider taxonomic diversity representative of biological diversity, and if we want our SSP programs to preserve biodiversity, then we would want SSP programs representative of all families. McDowell [1987] lists 16 families of living snakes (Table 5) . Since we estimated above that we may be able to accommodate up to 16 species of snakes, then a representative species from each family may be possible. However, exhibit value, obtainability of specimens, and husbandry success may prohibit inclusion of certain families in SSP programs (i.e., Families Anomal- epididae, Typhlopidae, Leptotyphlopidae, Aniliidae, Uropeltidae, Bolyeriidae).

254 Quinn and Quinn

These factors will also lead to some families having more than one representative. As a result, all families will probably not be represented by SSP programs. Therefore, to help preserve biodiversity, efforts should be made to at least include a representative from both infraorders. If a representative from each of the six superfamilies within the infraorder Alethinophidia was selected in addition to one representative from the infraorder Scolecophidia, this would constitute seven SSPs. Additional SSPs should be developed to represent as many families as possible. With this reasoning, we may have SSPs from the following families totaling about 16 species/SSP programs: Typhlopidae, Acrochordidae, Loxocemidae, Tropidopheidae, Pythonidae, Boidae, Elapidae, Colubridae, Viperidae.

CONCLUSIONS

Utilizing existing population genetics models, and making some justifiable assumptions regarding the life history information required in these models, the number of snake species that can be managed by Species Survival Plans (SSPs) was estimated. The following conclusions were drawn:

1. With no restrictions on enclosure theme or size, it is estimated that 16 snake species can be accommodated by SSP programs.

2. Restrictions on enclosure theme (Table 3) will reduce the number of snake species that can be accommodated by SSP programs to 13.

3. Restrictions on enclosure size (Table 3) will affect the size of snake species accommodated by SSP programs. It is estimated that one species of giant snake and 15 species of small snakes can be maintained in SSP programs.

4. Ways to increase the number of snake species accommodated by SSP programs were suggested: increase reserve space, devote more space for SSP snakes, lengthen generation time, promote gene exchange with wild populations, goal SSP programs for < 200 years, invest in short-term programs, involve the private sector, build new enclosures, increase the number of snakes per enclosure, and encourage participation of non-North American institutions.

5. Finally, it was emphasized that taxa should be chosen carefully if diversity of snake species is to be represented, and that SSPs should be developed to represent as many snake families as possible. To maximize biological diversity in relation to captive carrying capacity in North American zoos, it is recommended that SSP programs represent both infraorders of living snakes (Scolecophidia and Alethino- phidia) and as many families within those infraorders as possible. It has been determined that as many as 16 SSP species can be accommodated in available enclosures, but factors such as exhibit value, obtainability, and husbandry success suggest that not all 16 families of snakes will be represented. However, it may be pdssible to represent as many as nine families of snakes in 16 SSP programs in North Am-erican zoos.

ACKNOWLEDGMENTS

The authors thank representatives from the following zoos and other institutions who responded to the survey: Abilene Zoological Gardens; Arizona Sonora Desert Museum; Audubon Park and Zoological Garden; Birmingham Zoo; Brookfield Zoo;


Buffalo Zoological Gardens; Central Texas Zoo; Chaffee Zoological Gardens of Fresno; Cincinnati Zoo and Botanical Garden; Columbus Zoological Gardens; Dallas Zoo; Detroit Zoological Park; Dickerson Park Zoo; El Paso Zoological Park; Fort Worth Zoological Park; Hogle Zoological Garden; Houston Zoological Gardens; In- dianapolis Zoo; Institute for Herpetological Research; Knoxville Zoological Park; Little Rock Zoological Gardens; Los Angeles Zoo; Louisville Zoological Garden; Memphis Zoological Garden and Aquarium; Metro Toronto Zoo; Miami Metrozoo; Minnesota Zoological Garden; New York Zoological Park (Bronx Zoo); North Caro- lina Zoological Park; Oklahoma City Zoological Park; Phoenix Zoo; Rio Grande Zoological Park; Riverbanks Zoological Park; Sacramento Zoo; St. Louis Zoological Park; San Antonio Zoological Gardens and Aquarium; Sedgwick County Zoo and Botanical Garden; Staten Island Zoo; Toledo Zoological Gardens; Topeka Zoological Park; Tulsa Zoological Park; Woodland Park Zoological Gardens; Zoo Atlanta; and one unidentified respondent. Thanks also to Michael Hutchins and Robert Wiese for critically reviewing the manuscript.

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Boyd, L.J., ed. ZOOLOGICAL PARKS AND

1991. Wheeling, WV, American Association of Zoological Parks and Aquariums, 1990.

Diebold, E.; Hutchins, M. A challenge of the 1990s: Zoo bird collection planning. Pp. 244- 252 in AAZPA REGIONAL CONFERENCES, 1991.

Dodd, K.C. Status, conservation, and management. Pp. 478-513 in SNAKES: ECOLOGY AND EVOLUTIONARY BIOLOGY. R. Seigel; J.T. Collins; S . Novak, eds., New York, Mac- millan, 1987.

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estimated number of snake species that can be managed by species survival plans in north america

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