Orangutan (Pongo pygmaeus + Pongo abelii) AZA Animal Programs Population Viability Analysis Report

Transcription

1 Orangutan (Pongo pygmaeus + Pongo abelii) AZA Animal Programs Population Viability Analysis Report Population Biologist Brent Johnson, bjohnson@lpzoo.org AZA Animal Program Leader Lori Perkins, lperkins@zooatlanta.org Regional Studbook Keeper & AZA Vice-Animal Program Leader Megan Elder, megan.elder@ci.stpaul.mn.us AZA Ape TAG Chair Tara Stoinski, tstoinski@zooatlanta.org AZA Ape TAG Vice-Chair Tracy Fenn, fennt@jacksonvillezoo.org August 19, 2014

2 TABLE OF CONTENTS EXECUTIVE SUMMARY...2 POPULATION VIABILITY ANALYSIS (PVA) APPROACH...3 REPORT OVERVIEW...4 HYBRID POPULATION VIABILITY UNDER CURRENT MANAGEMENT...5 BORNEAN POPULATION HISTORY AND CURRENT STATUS...6 BORNEAN MODEL SCENARIOS...9 BORNEAN POPULATION VIABILITY UNDER CURRENT MANAGEMENT...10 BORNEAN ALTERNATE MODEL SCENARIOS...11 SUMATRAN POPULATION HISTORY AND CURRENT STATUS...13 SUMATRAN MODEL SCENARIOS...16 SUMATRAN POPULATION VIABILITY UNDER CURRENT MANAGEMENT...17 SUMATRAN ALTERNATE MODEL SCENARIOS...18 MANAGEMENT ACTIONS...19 CONCLUSIONS...19 ACKNOWLEDGEMENTS...20 LITERATURE CITED...21 DEFINITIONS...22 APPENDICES Population Viability Analyses for AZA Orangutan Animal Program 1

3 EXECUTIVE SUMMARY Population Viability Analyses (PVA) are being conducted by Lincoln Park Zoo and Population Management Center researchers through funding from the Institute of Museum and Library Services (IMLS). The project team uses ZooRisk 3.80 (Earnhardt et al. 2008), a PVA modeling software, to examine what would happen to AZA populations if current conditions remain the same (the baseline scenario), and then assess the impact of changes in reproductive rates, space availability, imports/exports, and other potential management actions (alternate scenarios). Model scenarios for this population were developed with members of the Association of Zoos and Aquarium (AZA) Ape Taxon Advisory Group (TAG) during summer of POPULATION HISTORY/CURRENT STATUS Bornean orangutans (Pongo pygmaeus) have been consistently held in AZA institutions since Through a combination of importations of animals from outside of AZA and zoo births, the population grew to a size near 75 individuals by The population currently includes 84 individuals. In the past 10 years, the population has had an average of 2.7 births/year. Current gene diversity is high (97.2%) and inbreeding is low (average inbreeding coefficient of ). Sumatran orangutans (Pongo abelii) have been consistently housed in North American institutions since 1928, although the population size remained low (<30 individuals) until After that year, the population grew through a combination of importations of animals from outside of the formally managed population and zoo births to a peak size of 105 individuals in The population averaged 2.8 births/year in the past 10 years and currently includes 85 individuals. At present, the Sumatran orangutan population has high gene diversity (97.6%) and low inbreeding (average inbreeding coefficient of ). For each orangutan population, managers have been moving toward a standard of parent rearing and more prolonged time that offspring spend with their mother. They intend to maintain a minimum of 8-year interbirth intervals among females (except when infant mortalities occur) to allow them to fully raise their young. PVA RESULTS Model results indicate that hybrid orangutans will age out of AZA institutions in approximately 32 years, which could increase spaces for the other orangutan populations. If the AZA Bornean orangutan population continues its current breeding rate (2.7 births/year in the past 10 years), it is expected to have a 4% chance of extinction or approximately 16 individuals remaining in 100 years. However, increasing breeding is predicted to allow the AZA Bornean orangutan population to remain stable over the next 100 years. For the population to maintain its current size, it would need to produce an average of ~4 births per year over the next 10 years. If the population produces ~5 births/year, it could fill 115 potential spaces (including half of those currently occupied by hybrids) in approximately 32 years. Under its current breeding rate (2.8 births/year in the past 10 years), the formally managed Sumatran orangutan population is predicted to decline to an average of 50 individuals over the next 100 years. Increasing breeding is predicted to also allow the Sumatran orangutan population to remain stable over the next 100 years. To maintain its current size, the population should produce an average of ~4 births per year over the next 10 years. By producing ~4 births/year over the next decade and ~5 births every following year, the population could fill 115 potential spaces in approximately 33 years. Increasing breeding rates (to either maintain the current population size or fill potential spaces) is also expected to maintain the genetic health of each orangutan population over the next century. MANAGEMENT ACTIONS The AZA Orangutan Animal Programs should consider the following changes to current management strategies: Re-allocate spaces currently occupied by hybrids as they become available: Because spaces are expected to become available as hybrid orangutans age out of AZA institutions, managers should ensure that these spaces are allocated to Bornean and Sumatran orangutans to maintain each of these populations at a larger, stable size with the best possible genetic health. Increase breeding rates: For each orangutan population, breeding should be increased from ~3 births per year to a minimum of ~4 births each year to maintain the current population size. To fill spaces currently occupied by hybrid orangutans as they become available, the Bornean population should produce ~5 births per year. The Sumatran population, however, should produce ~4 births each year for the next decade and ~5 births every following year in order to do so. To achieve these higher breeding rates, it may not be possible to immediately implement the recommended 8-year interbirth intervals. If higher breeding rates could be maintained, each population may become demographically stable and maintain its genetic health Population Viability Analyses for AZA Orangutan Animal Program 2

4 FULL REPORT POPULATION VIABILITY ANALYSIS (PVA) APPROACH A Population Viability Analysis (PVA) is a model that projects the likely future status of a population. PVAs are used to evaluate long-term demographic and genetic sustainability and extinction risk, identify key factors impacting a population s dynamics, and compare alternative management strategies. This PVA utilizes ZooRisk, a computer software package that models the future dynamics of a cooperatively-bred population using that population s age and sex structure, mortality and reproductive rates, and genetic structure (Earnhardt et al., 2008). ZooRisk is individual-based, meaning it tracks every animal (current and future) in the population over time. It also includes stochasticity, the randomness in mortality, fecundity, and birth sex ratios among individuals, which is especially important for small populations. Because of this stochasticity, we run each model many times, allowing us to determine the range of potential outcomes a population could experience under a given set of conditions. The most powerful use of PVAs is to compare a baseline scenario, reflecting the population s likely future trajectory if no management changes are made, to alternate scenarios reflecting potential management changes. For zoo and aquarium populations, these alternate scenarios typically involve varying breeding rates (probability of breeding, or p(b)), potential space for the population, importation or exportation rates, mortality rates, or genetic management strategies. These comparisons can help evaluate the relative costs and benefits of possible management actions. Because the future can be uncertain and difficult to predict, model results are most appropriately used to compare between scenarios (e.g. relative to each other) rather than as absolute predictions of what will happen. Full documentation on ZooRisk can be found in the software s manual (Faust et al., 2008); complete details on the modeling approach for this PVA, including data sources, parameter values, and model setup, can be found in Appendix A Population Viability Analyses for AZA Orangutan Animal Program 3

5 Number of Individuals REPORT OVERVIEW Orangutans in the entire, formally managed population (i.e., at AZA institutions and Toronto Zoo) have historically included individuals of both the Bornean (Pongo pygmaeus) and Sumatran species (Pongo abelii), as well as hybrids of the two and individuals of unknown origin (Fig. 1). Today, relatively even numbers of Bornean and Sumatran orangutans are held among these institutions (84 Bornean orangutans and 85 Sumatran orangutans), with 45 remaining individuals being hybrids. In this report we very briefly present a scenario pertaining to the hybrid population, and then separately describe the population history, status, and model results for the Bornean and Sumatran orangutan populations Sumatran Bornean Hybrid Unknown Year Figure 1. Number of orangutans in the entire, formally managed population since Population Viability Analyses for AZA Orangutan Animal Program 4

6 Number of Individuals HYBRID POPULATION VIABILITY UNDER CURRENT MANAGEMENT Currently, 45 hybrid orangutans (21 males, 24 females) are housed at 23 AZA institutions. The majority of these individuals are currently above 25 years old (Fig. 2). Because hybrids exist in zoos only as a result of breeding that occurred prior to the recognition of two distinct orangutan species, the Ape TAG plans to manage the hybrid population without any further reproduction. In this management scenario, the hybrid population can be expected to age out of zoos in approximately 32 years (Fig. 3, Table 1). Table 1. Baseline model results. SCENARIO Initial Population Size DEMOGRAPHICS Size in Year 25 1 Size in Year Reaching Spaces Probability of (%) Probability of Extinction (%) Median Years until Reaching Extinction A p(b) = 0% 45 2 ± Mean value + 1 Standard Deviation, taken across 1000 iterations. If an iteration goes extinct that value is not included in the calculation, so results may only reflect a few iterations in scenarios with a high probability of extinction. Figure 2. The age distribution of the total hybrid population (21.24) within AZA institutions. A) p(b) = 0% Historic Year Figure 3. Historical and projected mean population size with no future breeding. Projected results are averaged across 1000 model iterations Population Viability Analyses for AZA Orangutan Animal Program 5

7 Number of Individuals Number of Individuals Number of Individuals BORNEAN POPULATION HISTORY AND CURRENT STATUS Demographics Based on the international orangutan studbook (Elder, 2014), Bornean orangutans have been consistently held in AZA institutions since Initial growth of the population was driven exclusively by importations of wild-caught individuals (Figs. 4 and 5a). (Note that throughout this section, imports are animals entering AZA institutions which may be coming from non-aza institutions such as the private sector, EAZA, other zoo regions, or from the wild, and conversely exports are animals exiting AZA institutions and going into non-aza populations, such as other zoo regions or being released into the wild). Regular breeding of Bornean orangutans in AZA zoos began in 1960, when the population size was 39 individuals. Since 1969, the population has remained above approximately 70 individuals (Fig. 4). The population peaked in size at 89 individuals in Total s s Year Figure 4. Number of Bornean orangutans in AZA institutions since Births Imports Year a) b) 10 9 Deaths Exports Year Figure 5. Number of a) births and imports and b) deaths and exports in the population since Imported animals entering AZA institutions may be coming from non-aza institutions (private sector, EAZA, other zoo regions, or from the wild); exported animals may be going to other institutions outside of AZA in North America, other regions, or being released into the wild. Over the last 10 years ( , based on the studbook currentness date), the Bornean orangutan population has increased slightly in size from 78 to 84 individuals and has experienced an average annual growth rate of 0.6%, although specific annual growth rates have ranged from -6.8% to +7.2% (Table 2). The population has averaged 0.0% annual growth in the past five years. In the past decade, the population has averaged 2.7 births per year (which corresponds to each female having an 11.5% probability of breeding in a given year; see Appendix A) and 0.4 imports each year. As of April 26 th, 2014 (the studbook currentness date), the Bornean orangutan population consisted of 84 animals (33 males, 51 females). Five females are excluded from the breeding population, based on being beyond the reproductive age window (14-42; see Appendix A) or being sterile. This leaves a potentially breeding population of 79 (33.46) individuals. See Appendix B for a complete list Table 2. Summary of demographic statistics for the AZA population. Population Sizes Total (male.female.unknown) Current population 84 ( ) Potentially breeding population 79 ( ) Annual rates over the last decade Mean (min-max) Population Growth (Lambda, λ) ( ) Births 2.7 (1-7) Deaths 2.6 (0-7) Imports 0.4 (0-4) Exports Population Viability Analyses for AZA Orangutan Animal Program 6

8 of the individuals included in the model and their reproductive status. The population has an age structure that is largely columnar with many empty age classes (Fig. 6a). There are also few individuals in lower age classes due to somewhat low reproduction in the past seven years. The potentially breeding population currently displays a female-biased sex ratio of 1.4 females per male (Fig. 6b). Orangutans generally breed best when held in groups with 1 to 3 females per male, therefore the current sex ratio is appropriate for the management of this population. a) b) Figure 6. The population s age distribution within AZA institutions, divided into a) the total population 84 ( ) and b) the potentially breeding population 79 ( ). Genetics The Bornean orangutan population s pedigree is 100% known (Table 3), and no analytical assumptions were necessary. The managed population is descended from 50 founders with no additional potential founders remaining in the population. Current gene diversity is estimated to be 97.23%. As gene diversity falls, reproduction may become increasingly compromised by lower birth weights, greater neonatal mortality, and other negative factors. Table 3. Summary of starting genetic statistics for the population. Percentage of pedigree known 100% Genetic Diversity (GD) 97.23% Population mean kinship (MK) Mean inbreeding (F) Mean generation time (T) (years) 20.9 Number of generations in 100 model years 4.8 The population has a low mean inbreeding level of (a mean inbreeding coefficient of is equivalent to mating between first cousins with no prior inbreeding). One of the largest genetic threats to small populations is the potential for inbreeding depression, in which breeding between close relatives results in reductions in fecundity or litter size, increases in infant mortality, and other detrimental effects (DeRose and Roff, 1999; Koeninger Ryan, et al., 2002; Ballou and Foose, 1996; Reed and Frankham, 2003). Given the low level of inbreeding in the Bornean orangutan population, the small number of individuals with inbreeding values above 0 prevented us from statistically testing for possible effects on infant mortality. It is unlikely that inbreeding is impacting the population at this time; however, inbreeding may become a threat in the future and should therefore be avoided. Because modeling inbreeding depression adds an additional layer of complexity to interpretation of results, we have not included a standard inbreeding depression effect in the PVA models. There are several strategies that can delay the effects or lower the probability of inbreeding depression including pairing based on mean kinship and importing and breeding unrelated individuals (Ballou and Lacy, 1995). These strategies were modeled for 2014 Population Viability Analyses for AZA Orangutan Animal Program 7

9 Interbirth Interval (Years) all scenarios except those without genetic management. Because inbreeding depression is not included, readers should consider that model results may be optimistic if inbreeding depression begins to impact the population. Management ZooRisk can include a space limitation on population growth, reducing breeding as the population approaches the potential space limit. This mimics the way a population manager would recommend fewer pairs when at capacity. To accurately model the potential space for a population, we use either a) the projected spaces in 5 years based on a TAG s Regional Collection Plan (RCP) or, if that value is unavailable or inappropriate, b) the current population size + 10% or 10 individuals, whichever is greater. These values are also placed in context of current institutional interest by the Species Coordinator. The Ape TAG s most recent space survey set the target size for Bornean orangutans over 4 years old at 85 individuals (AZA Ape Taxon Advisory Group, 2007), however some additional spaces could become available if the population grows. Given this fact, and because animals under 4 four years old still occupy space in ZooRisk, we allowed for 100 potential spaces in our model. The AZA Bornean orangutan population is currently designated as a Green Program. The population is housed at 25 institutions, with 21 having at least one potential breeding pair. Since the late 1980s, parent rearing has become the primary means of raising young Bornean orangutans in zoos (Fig. 7). Additionally, there has been an increasing trend in the interbirth intervals among females raising offspring. Managers intend to have interbirth intervals no shorter than 8 years except when infant mortalities occur to ensure proper social development of the offspring. If reproductively viable females in the population were to maintain an average interbirth interval of 8 years, the female probability of breeding (p[b]) in any given year would be equal to 12.5% (see appendix A for more information on p[b]) Parent Hand Foster Supplemental Unknown Trend (Parent) Year Figure 7. Interbirth intervals related to each rearing style over time Population Viability Analyses for AZA Orangutan Animal Program 8

10 BORNEAN MODEL SCENARIOS Model scenarios were created to reflect what would happen if current management approaches continued (baseline) and to address potential alternate management strategies (Table 4). Model setup is described more fully in Appendix A. Scenarios are described in more detail in the following sections. Table 4. ZooRisk Model Scenarios Scenario Name Scenario Description p(b) Spaces Baseline Scenario: B. Baseline; p(b) = 11.5% Reproduction to match past 10 years (2.7 births/year) 11.5% 100 Alternate Scenarios: C. p(b) = 19% Reproduction required to sustain current population size 19% 100 D. p(b) = 25%; spaces = 115 p(b) = Probability of Breeding Reproduction required to fill hybrid spaces as they become available (i.e., approaching 115 spaces over the next 32 years) 25% Population Viability Analyses for AZA Orangutan Animal Program 9

11 Number of Individuals BORNEAN POPULATION VIABILITY UNDER CURRENT MANAGEMENT BASELINE MODEL PVA RESULTS We examined the viability of the AZA Bornean orangutan population under current management: 11.5% female probability of breeding (equivalent to 2.7 births/year over the past 10 years) and no imports or exports. The population currently has a target size of 85 for individuals older than 4 years old, however some additional spaces could become available if the population grows. Because of this flexibility in the availability of spaces, and the fact that animals younger than 4 years old hold space within our models, we allowed for 100 potential spaces in the baseline scenario. See Appendix A for full details on all model parameters. If the current breeding rate continues, the Bornean orangutan population has a 4% chance of reaching extinction (Table 5). If it does not go extinct, the population is expected to have approximately 16 individuals remaining in 100 years (Table 5, Fig. 8). In this scenario, the population would retain 84.4% gene diversity and fairly low inbreeding (average inbreeding coefficient (F) = 0.055) after 100 years, although inbreeding would begin approaching the equivalent of mating between first cousins (F = 0.063). The population is predicted to have a Vulnerable risk status in zoos and aquariums due to its declining gene diversity (see Appendix C) B. Bornean baseline; p(b) = 11.5% Historic Potential Space Year Figure 8. Historical and projected mean population size under the baseline model scenario. Projected results are averaged across 1000 model iterations. Table 5. Baseline model results. SCENARIO Initial Population Size Size in Year 25 1 DEMOGRAPHICS Size in Year Probability of Reaching Spaces (%) Probability of Extinction (%) Initial GD (%) GD Retained in Year GENETICS Initial F B p(b) = 11.5% ± 9 16 ± ± F Retained in Year ± OVERALL POPULATION STATUS 2 Vulnerable GD = gene diversity, F = inbreeding coefficient 1 Mean value + 1 Standard Deviation, taken across 1000 iterations. If an iteration goes extinct that value is not included in the calculation, so results may only reflect a few iterations in scenarios with a high probability of extinction. 2 ZooRisk uses five standardized tests to give a summary risk score for each scenario, from Low Risk (most secure), Vulnerable, Endangered, to Critical (least secure). For more details on this score, see Appendix C Population Viability Analyses for AZA Orangutan Animal Program 10

12 BORNEAN ALTERNATE MODEL SCENARIOS We explored the impacts of altering the probability of breeding for the Bornean orangutan population in order to maintain the population at its current size or increase the population to fill all potential spaces. For the population to sustain its current size of 84 individuals for the next 100 years (Fig. 9, Table 6), it needs to produce an average of ~4 births/year (p(b) = 19%, scenario C; Fig. 10). Under this breeding rate, the population is expected to maintain high gene diversity (94.3%) and fairly low inbreeding (mean inbreeding coefficient (F) = 0.043) over the next 100 years, although inbreeding would begin approaching the equivalent of mating between first cousins (F = 0.063). Note that a p(b) = 19% is approximately equivalent to reproductively viable females in the population maintaining an average interbirth intervals of 5.3 years. This interval could account for infant mortality, meaning that females who lost infants would likely have shorter interbirth intervals while those that had surviving infants could have longer ones. We estimate that 115 potential spaces could be available for the Bornean orangutan population after hybrids age out of AZA zoos in approximately 32 years (scenario A; Table 1), which is equal to the population s target size of 85 individuals plus ~8 spaces for offspring and half of spaces previously occupied by hybrids (~22 spaces). If the population produces an average of ~5 births/year, it could fill the 115 potential spaces in approximately 32 years (p(b) = 25%, scenario D; Figs. 9 and 10). A p(b) = 25% is equivalent to every reproductively viable female in the population maintaining an average interbirth interval of 4 years (which would be an average of intervals with the first offspring living and the first offspring not surviving). In this management scenario, the population would maintain high gene diversity (95.1%) and fairly low inbreeding levels (F = 0.039) over the next century (Table 6). In both increased breeding scenarios, the population is projected to retain a Low Risk status in zoos (Appendix C). Table 6. Model results for all Bornean orangutan scenarios. SCENARIO Initial Population Size Size in Year 25 1 DEMOGRAPHICS Size in Year Probability of Reaching Spaces (%) Probability of Extinction (%) Initial GD (%) GD Retained in Year GENETICS Initial F B p(b) = 11.5% ± 9 37 ± ± C p(b) = 19% ± ± ± D p(b) = 25%; spaces = ± ± ± F Retained in Year ± ± ± OVERALL POPULATION STATUS 2 Vulnerable Low Risk Low Risk GD = gene diversity, F = inbreeding coefficient 1 Mean value + 1 Standard Deviation, taken across 1000 iterations. If an iteration goes extinct that value is not included in the calculation, so results may only reflect a few iterations in scenarios with a high probability of extinction. 2 ZooRisk uses five standardized tests to give a summary risk score for each scenario, from Low Risk (most secure), Vulnerable, Endangered, to Critical (least secure). For more details on this score, see Appendix C Population Viability Analyses for AZA Orangutan Animal Program 11

13 Number of Individuals Number of Hatches C. Bornean; p(b) = 19% D. Bornean; p(b) = 25%; space = 115 Potential Space Historic Year Figure 9. Historical and projected mean population size under alternate model scenarios. Projected results are averaged across 1000 model iterations C. Bornean; p(b) = 19% D. Bornean; p(b) = 25%; space = 115 Past 10 Years Year Figure 10. Number of total births in the AZA population in the past decade and projected mean number of births under alternate model scenarios. Projected results are averaged across 1000 model iterations Population Viability Analyses for AZA Orangutan Animal Program 12

14 Number of Individuals Number of Individuals Number of Individuals Demographics SUMATRAN POPULATION HISTORY AND CURRENT STATUS Based on the international orangutan studbook (Elder, 2014), Sumatran orangutans have been consistently held in AZA zoos and one non-aza partner institution (Toronto Zoo) since However, the population size remained low (<30 individuals) until 1960 (Fig. 11). Regular breeding of Sumatran orangutans within the formally managed population began the following year (Fig. 12a). Initial population growth was driven by importations of wildcaught individuals, as well as zoo births, and the population reached over 80 individuals in 1969 (Fig. 11). (Note that throughout this section, imports are animals entering the formally managed population which may be coming from outside institutions such as the private sector, EAZA, other zoo regions, or from the wild, and conversely exports are animals exiting the formally managed population and going into other populations, such as other zoo regions or being released into the wild). In 1997, the Sumatran orangutan population size peaked at 105 individuals Births Imports Year a) b) Deaths Exports Year Figure 12. Number of a) births and imports and b) deaths and exports in the population since Imported animals entering the formally managed population may be coming from outside institutions (private sector, EAZA, other zoo regions, or from the wild); exported animals may be going to other institutions outside of the formally managed in North America, other regions, or being released into the wild Total s s Year Figure 11. Number of Sumatran orangutans in the formally managed population since Over the last 10 years ( , based on the studbook currentness date), the formally managed population has decreased slightly in size from 91 to 85 individuals and has experienced an average annual growth rate of -0.4%, although specific annual growth rates have ranged from -6.8% to +4.9% (Table 7). The population has averaged +1.2% annual growth in the past five years. In the past decade, the population has had an average of 2.8 births per year (which corresponds to each female having a 14.8% probability of breeding in a given year; see Appendix A), as well as an average of 0.2 imports and 0.2 exports each year. As of April 26 th, 2014 (the studbook currentness date), the Sumatran orangutan population consisted of 85 individuals (36 males, 48 females, 1 unknown). Seventeen animals (2 males, 15 females) are excluded Table 7. Summary of demographic statistics for the population. Population Sizes Total (male.female.unknown) Current population 85 ( ) Potentially breeding population 68 ( ) Annual rates over the last decade Mean (min-max) Population Growth (Lambda, λ) ( ) Births 2.8 (1-4) Deaths 3.2 (0-7) Imports 0.2 (0-1) Exports 0.2 (0-1) 2014 Population Viability Analyses for AZA Orangutan Animal Program 13

15 from the breeding population, based on being beyond the reproductive age window (10-45 for males, for females; see Appendix A), having health or behavioral issues, or being sterile. This leaves a potentially breeding population of 68 ( ) individuals. See Appendix B for a complete list of the individuals in the model and their reproductive status. The formally managed population has an age structure that is largely columnar with many empty age classes (Fig. 13a). The potentially breeding population currently displays an even sex ratio (Fig. 13b). Orangutans generally breed best when held in groups with 1 to 3 females per male, therefore the current sex ratio is appropriate for the management of this population. However, managers are concerned about the loss of females from the potentially breeding population, which could cause a male-biased sex ratio. a) b) Figure 13. The population s age distribution within AZA and partner institutions, divided into a) the total population 85 ( ) and b) the potentially breeding population 68 ( ). Genetics The Sumatran orangutan population s pedigree is 100% known (Table 8), and no analytical assumptions were necessary. The managed population is descended from 50 founders with no additional potential founders remaining in the population. Current gene diversity is estimated to be 97.58%. As gene diversity falls, reproduction may become increasingly compromised by lower birth weights, greater neonatal mortality, and other negative factors. Table 8. Summary of starting genetic statistics for the population. Percentage of pedigree known 100% Genetic Diversity (GD) 97.58% Population mean kinship (MK) Mean inbreeding (F) Mean generation time (T) (years) 24.7 Number of generations in 100 model years 4.0 The population has a low mean inbreeding level of (a mean inbreeding coefficient of is equivalent to mating between first cousins with no prior inbreeding). One of the largest genetic threats to small populations is the potential for inbreeding depression, in which breeding between close relatives results in reductions in fecundity or litter size, increases in infant mortality, and other detrimental effects (DeRose and Roff, 1999; Koeninger Ryan, et al., 2002; Ballou and Foose, 1996; Reed and Frankham, 2003). Given the low level of inbreeding in the Sumatran orangutan population, the small number of individuals with inbreeding values above 0 prevented us from statistically testing for possible effects on infant mortality. It is unlikely that inbreeding is impacting the population at this time; however, inbreeding may become a threat in the future and should therefore be avoided. Because modeling inbreeding depression adds an additional layer of complexity to 2014 Population Viability Analyses for AZA Orangutan Animal Program 14

16 Interbirth Interval (Years) interpretation of results, we have not included a standard inbreeding depression effect in the PVA models. There are several strategies that can delay the effects or lower the probability of inbreeding depression including pairing based on mean kinship and importing and breeding unrelated individuals (Ballou and Lacy, 1995). These strategies were modeled for all scenarios except those without genetic management. Because inbreeding depression is not included, readers should consider that model results may be optimistic if inbreeding depression begins to impact the population. Management ZooRisk can include a space limitation on population growth, reducing breeding as the population approaches the potential space limit. This mimics the way a population manager would recommend fewer pairs when at capacity. To accurately model the potential space for a population, we use either a) the projected spaces in 5 years based on a TAG s Regional Collection Plan (RCP) or, if that value is unavailable or inappropriate, b) the current population size + 10% or 10 individuals, whichever is greater. These values are also placed in context of current institutional interest by the Species Coordinator. The Ape TAG s most recent space survey set the target size for Sumatran orangutans over 4 years old at 85 individuals (AZA Ape Taxon Advisory Group, 2007), however some additional spaces could become available if the population grows. Given this fact, and because animals under 4 four years old still occupy space in ZooRisk, we allowed for 100 potential spaces in our model. The AZA Sumatran orangutan population is currently designated as a Green Program. The formally managed population is housed at 28 institutions, including one non-aza institution (Toronto Zoo). Nineteen institutions have at least one potential breeding pair. Since the late 1980s, parent rearing has become the primary means of raising young Sumatran orangutans in zoos (Fig. 14). Additionally, there has been an increasing trend in the interbirth intervals among females raising offspring. Managers intend to have interbirth intervals no shorter than 8 years except when infant mortalities occur to ensure proper social development of the offspring. If reproductively viable females in the population were to maintain an average interbirth interval of 8 years, the female probability of breeding (p[b])in any given year would be equal to 12.5% (see appendix A for more information on p[b]) Parent Hand Foster Supplemental Unknown Trend (Parent) Year Figure 14. Interbirth intervals related to each rearing style over time Population Viability Analyses for AZA Orangutan Animal Program 15

17 SUMATRAN MODEL SCENARIOS Model scenarios were created to reflect what would happen if current management approaches continued (baseline) and to address potential alternate management strategies (Table 9). Model setup is described more fully in Appendix A. Scenarios are described in more detail in the following sections. Table 9. ZooRisk Model Scenarios Scenario Name Scenario Description p(b) Spaces Baseline Scenario: E. Baseline; p(b) = 14.8% Reproduction to match past 10 years (2.8 births/year) 14.8% 100 Alternate Scenarios: F. p(b) = 18% Reproduction required to sustain current population size 18% 100 G. p(b) = 25%; spaces = 115 Reproduction required to fill hybrid spaces as they become available (i.e., approaching 115 spaces over the next 32 years) 25% 115 p(b) = Probability of Breeding 2014 Population Viability Analyses for AZA Orangutan Animal Program 16

18 Number of Individuals SUMATRAN POPULATION VIABILITY UNDER CURRENT MANAGEMENT BASELINE MODEL PVA RESULTS We examined the viability of the formally managed Sumatran orangutan population under current management: 14.8% female probability of breeding (equivalent to 2.8 births/year over the past 10 years) and no imports or exports. The population currently has a target size of 85 for individuals older than 4 years old, however some additional spaces could become available if the population grows. Because of this flexibility in the availability of spaces, and the fact that animals younger than 4 years old hold space within our models, we allowed for 100 potential spaces in the baseline scenario. See Appendix A for full details on all model parameters. Under its current breeding rate, the Sumatran orangutan population is expected to decline to approximately 50 individuals over the next 100 years (Fig. 15). However, the population would retain high gene diversity (92.2%) and fairly low inbreeding (average inbreeding coefficient (F) = 0.049) after 100 years, although inbreeding would begin approaching the equivalent of mating between first cousins (F = 0.063; Table 10). The population is predicted to maintain a Low Risk status in zoos and aquariums over the next century (see Appendix C) E. Sumatran baseline; p(b) = 14.8% Historic Potential Space Year Figure 15. Historical and projected mean population size under the baseline model scenario. Projected results are averaged across 1000 model iterations. Table 10. Baseline model results. SCENARIO Initial Population Size Size in Year 25 1 DEMOGRAPHICS Size in Year Probability of Reaching Spaces (%) Probability of Extinction (%) Initial GD (%) GD Retained in Year GENETICS Initial F E p(b) = 14.8% ± 9 50 ± ± F Retained in Year ± OVERALL POPULATION STATUS 2 Low Risk GD = gene diversity, F = inbreeding coefficient 1 Mean value + 1 Standard Deviation, taken across 1000 iterations. If an iteration goes extinct that value is not included in the calculation, so results may only reflect a few iterations in scenarios with a high probability of extinction. 2 ZooRisk uses five standardized tests to give a summary risk score for each scenario, from Low Risk (most secure), Vulnerable, Endangered, to Critical (least secure). For more details on this score, see Appendix C Population Viability Analyses for AZA Orangutan Animal Program 17

19 SUMATRAN ALTERNATE MODEL SCENARIOS We explored the impacts of altering the probability of breeding for the Sumatran orangutan population in order to maintain the population at its current size or increase the population to fill all potential spaces. For the population to sustain its current size of 85 individuals for the next 100 years (Fig. 16, Table 11), it needs to produce an average of ~4 births/year (p(b) = 18%, scenario F; Fig. 17). Under this breeding rate, the population is expected to maintain high gene diversity (94.2%) and fairly low inbreeding (F = 0.047) at 100 years, although inbreeding would begin approaching the equivalent of mating between first cousins (F = 0.063). Note that a p(b) = 18% is approximately equivalent to reproductively viable females in the population maintaining an average interbirth interval of 5.6 years. This interval could account for infant mortality, meaning that females who lost infants would likely have shorter interbirth intervals while those that had surviving infants could have longer ones. We estimate that 115 potential spaces could be available for the Sumatran orangutan population after hybrids age out of AZA zoos in approximately 32 years (scenario A; Table 1), which is equal to the population s target size of 85 individuals plus ~8 spaces for offspring and half of spaces previously occupied by hybrids (~22 spaces). If the population produces an average of ~4 births/year over the next decade and ~5 births/year every following year, it could fill the 115 potential spaces in approximately 33 years (p(b) = 25%, scenario G; Figs. 16 and 17). A p(b) = 25% is equivalent to every reproductively viable female in the population maintaining an average interbirth interval of 4 years (which would be an average of intervals with the first offspring living and the first offspring not surviving). In this management scenario, the population would maintain high gene diversity (95.3%) and fairly low inbreeding (F = 0.040) over the next 100 years (Table 11). In either increase breeding scenario, the Sumatran orangutan population is projected to retain a Low Risk status in zoos (Appendix C). Table 11. Model results for all Sumatran orangutan scenarios. SCENARIO Initial Population Size Size in Year 25 1 DEMOGRAPHICS Size in Year Probability of Reaching Spaces (%) Probability of Extinction (%) Initial GD (%) GD Retained in Year GENETICS Initial F E p(b) = 14.8% ± 9 50 ± ± F p(b) = 18% ± ± ± G p(b) = 25%; spaces = ± ± ± F Retained in Year ± ± ± OVERALL POPULATION STATUS 2 Low Risk Low Risk Low Risk GD = gene diversity, F = inbreeding coefficient 1 Mean value + 1 Standard Deviation, taken across 1000 iterations. If an iteration goes extinct that value is not included in the calculation, so results may only reflect a few iterations in scenarios with a high probability of extinction. 2 ZooRisk uses five standardized tests to give a summary risk score for each scenario, from Low Risk (most secure), Vulnerable, Endangered, to Critical (least secure). For more details on this score, see Appendix C Population Viability Analyses for AZA Orangutan Animal Program 18

20 Number of Individuals Number of Hatches F. Sumatran; p(b) = 18% G. Sumatran; p(b) = 25%; space = Year Figure 16. Historical and projected mean population size under alternate model scenarios. Projected results are averaged across 1000 model iterations F. Sumatran; p(b) = 18% G. Sumatran; p(b) = 25%; space = Year Figure 17. Number of total births in the population in the past decade and projected mean number of births under alternate model scenarios. Projected results are averaged across 1000 model iterations. MANAGEMENT ACTIONS The AZA Orangutan Animal Programs should consider the following changes to current management strategies: Re-allocate spaces currently occupied by hybrids as they become available: Because spaces are expected to become available as hybrid orangutans age out of AZA institutions, managers should ensure that these spaces are allocated to Bornean and Sumatran orangutans to maintain each of these populations at a larger, stable size with the best possible genetic health. Increase breeding rates: For each orangutan population, breeding should be increased from ~3 births per year to a minimum of ~4 births each year to maintain the current population size. To fill spaces currently occupied by hybrid orangutans as they become available, the Bornean population should produce ~5 births per year. The Sumatran population, however, should produce ~4 births each year for the next decade and ~5 births every following year in order to do so. To achieve these higher breeding rates, it may not be possible to immediately implement the recommended 8-year interbirth intervals. If higher breeding rates could be maintained, each population may become demographically stable and maintain its genetic health. CONCLUSIONS This model is a scientifically-sound comprehensive tool to be used by population managers for assessing future directions for the animal program. This PVA report is provided to the AZA community and others to integrate into management of the important species within our care. The PVA model results are intended to provide the necessary data to make science-based decisions. Our model results illustrate that, under current management practices, each orangutan population can be expected to decline. Increasing breeding rates by approximately one or two births each year could ensure that each population maintains a stable size over the next 100 years. Additionally, allocating spaces currently occupied by hybrids to Bornean and Sumatran orangutans will help to better maintain the demographic and genetic stability of each of these populations. The AZA Orangutan Animal Programs should follow these recommended management strategies in order to keep both orangutan populations on the path towards long-term sustainability within AZA institutions Population Viability Analyses for AZA Orangutan Animal Program 19

21 ACKNOWLEDGEMENTS A meeting was conducted on June to discuss the Orangutan population and was attended by the following: Brent Johnson, Population Biologist, Lincoln Park Zoo, bjohnson@lpzoo.org Megan Elder, AZA Orangutan Animal Program Studbook Keeper, Como Park Zoo and Conservatory, megan.elder@ci.stpaul.mn.us Lauren Mechak, Assistant Population Biologist, Lincoln Park Zoo, lmechak@lpzoo.org Jennifer Michelberg, AZA Orangutan Population Advisor, jmichelberg@zooatlanta.org Lori Perkins, AZA Bornean and Sumatran Orangutan SSP Coordinator, Zoo Atlanta, lperkins@zooatlanta.org Adrienne Savrin, Research Assistant, Lincoln Park Zoo, asavrin@lpzoo.org Joseph L. Simonis, Post-doc at Alexander Center for Applied Population Biology, Lincoln Park Zoo, jsimonis@lpzoo.org This report was also reviewed by: Candice Dorsey, Director of Animal Programs, Association of Zoos and Aquariums, cdorsey@aza.org Megan Elder, AZA Orangutan Animal Program Studbook Keeper, Como Park Zoo and Conservatory, megan.elder@ci.stpaul.mn.us Lisa Faust, Vice President of Conservation and Science, Lincoln Park Zoo, lfaust@lpzoo.org Tracy Fenn, AZA Ape TAG Vice-Chair, Jacksonville Zoo and Gardens, fennt@jacksonvillezoo.org Lauren Mechak, Assistant Population Biologist, Lincoln Park Zoo, lmechak@lpzoo.org Lori Perkins, AZA Bornean and Sumatran Orangutan SSP Coordinator, Zoo Atlanta, lperkins@zooatlanta.org Adrienne Savrin, Research Assistant, Lincoln Park Zoo, asavrin@lpzoo.org Joseph L. Simonis, Post-doc at Alexander Center for Applied Population Biology, Lincoln Park Zoo, jsimonis@lpzoo.org Tara Stoinski, AZA Ape TAG Chair, Zoo Atlanta, tstoinski@zooatlanta.org If you have any questions about the report, please contact Lisa Faust at lfaust@lpzoo.org Analyses in this report utilized the International Orangutan (Pongo pygmaeus + Pongo abelii) Studbook current to 26 April 2014 (Elder, 2014) and was performed using Poplink 2.4 and ZooRisk 3.8. Funding provided by Institute of Museum and Library Services (IMLS) LG and MG to the Association of Zoos and Aquariums. Cover photo: courtesy of Megan Elder Citation: Johnson, B., Perkins, L., Elder, M., Stoinski, T., Fenn, T. Orangutan (Pongo pygmaeus + Pongo abelii) AZA Animal Program Population Viability Analysis Report. Lincoln Park Zoo, Chicago, IL. The contents of this report including opinions and interpretation of results are based on discussions between the project team and do not necessarily reflect the opinion or position of Lincoln Park Zoo, Association of Zoos and Aquariums, and other collaborating institutions. The population model and results are based on the project team s best understanding of the current biology and management of this population. They should not be regarded as absolute predictions of the population s future, as many factors may impact its future status Population Viability Analyses for AZA Orangutan Animal Program 20

22 LITERATURE CITED AZA Ape Taxon Advisory Group (TAG) Ape Advisory Group Regional Collection Plan (RCP) 3rd Edition. Ballou, J. D., and R. C. Lacy Identifying genetically important individuals for management of genetic variation in pedigreed populations. Pages in J. D. Ballou, M. Gilpin, and T. J. Foose, eds. Population Management for Survival and Recovery: Analytical Methods and Strategies in Small Population Conservation. Columbia University Press, New York. Ballou, J. D., and T. J. Foose Demographic and genetic management of captive populations. Pages in S. Lumpkin, ed. Wild Mammals in Captivity. University of Chicago Press, Chicago. DeRose, M. A., and D. A. Roff A comparison of inbreeding depression in life-history and morphological traits in animals. Evolution 53: Earnhardt, JM, Bergstrom, YM, Lin, A, Faust, LJ, Schloss, CA, and Thompson, SD ZooRisk: A Risk Assessment Tool. Version 3.8. Lincoln Park Zoo. Chicago, IL. Faust, LJ, Earnhardt, JM, Schloss, CA, and Bergstrom, YM ZooRisk: A Risk Assessment Tool. Version 3.8 User s Manual. Lincoln Park Zoo. Chicago, IL. Michelberg, J., Perkins, L., Elder, M. Orangutan (Pongo pygmaeus + Pongo abelii) AZA Species Survival Plan Green Program 2014 Population Analysis and Breeding & Transfer Plan. AZA Population Management Center, Chicago, IL. Zoo Atlanta, Atlanta, GA. Elder, M Orangutan (Pongo pygmaeus + Pongo abelii) AZA Studbook. Como Park Zoo and Conservatory, St. Paul, MN. Reed, D. H., and R. Frankham Correlation between fitness and genetic diversity. Conservation Biology 17: Population Viability Analyses for AZA Orangutan Animal Program 21

23 DEFINITIONS Age Structure: A two-way classification showing the numbers or percentages of individuals in various age and sex classes. Current Gene Diversity (GD): The proportional gene diversity (as a proportion of the source population) is the probability that two alleles from the same locus sampled at random from the population will not be identical by descent. Gene diversity is calculated from allele frequencies, and is the heterozygosity expected in progeny produced by random mating, and if the population were in Hardy-Weinberg equilibrium. Founder: An individual obtained from a source population (often the wild) that has no known relationship to any individuals in the derived population (except for its own descendants). Inbreeding Coefficient (F): Probability that the two alleles at a genetic locus are identical by descent from an ancestor common to both parents. The mean inbreeding coefficient of a population will be the proportional decrease in observed heterozygosity relative to the expected heterozygosity of the founder population. Mean Kinship (MK): The mean kinship coefficient between an animal and all animals (including itself) in the living, zoo born population. The mean kinship of a population is equal to the proportional loss of gene diversity of the descendant (zoo born) population relative to the founders and is also the mean inbreeding coefficient of progeny produced by random mating. Mean kinship is also the reciprocal of two times the founder genome equivalents: MK = 1 / (2 * FGE). MK = 1 - GD. Mean Generation Time (T): The average time elapsing from reproduction in one generation to the time the next generation reproduces. Also, the average age at which a female (or male) produces offspring. It is not the age of first reproduction. s and females often have different generation times. Percent Known: Percent of an animal's genome that is traceable to known Founders. Thus, if an animal has an UNK sire, the % Known = 50. If it has an UNK grandparent, % Known = 75% Population Viability Analysis (PVA): A PVA is a computer model that projects the likely future status of a population. PVAs are used for evaluating long-term sustainability, setting population goals, and comparing alternative management strategies. Several quantitative parameters are used in a PVA to calculate the extinction risk of a population, forecast the population s future trajectory, and identify key factors impacting the population s future. Potential Space: In the context of a Regional Collection Plan, the potential space selected for each Program within the RCP, which may be based on available spaces for that species, desired spaces the TAG wishes to allocate, the size needed to maintain a viable population, or some combination of those factors. In the context of the ZooRisk modeling work, the potential space is a model parameter that can be set at any level, including the size listed in the RCP or a higher or lower size based on other criteria. Probability of Breeding [p(b)]: p(b) is the age-specific probability that a female will have at least one offspring in a year. For example, p(b) = 25% is equivalent to females producing an offspring once every 4 years. Within the reproductively viable age classes, all p(b) were set at a hypothetical constant value corresponding with an interbirth interval, which varied depending on the model scenario. Using a constant value means that all reproductively viable females would have the same chance of reproduction regardless of age. Qx, Mortality: Probability that an individual of age x dies during time period. Regional Collection Plan (RCP): document developed by Taxon Advisory Group (TAG) to describe species managed under their TAG, level of management with explanations, and evaluation of Target Population Sizes for each managed species. Risk (Qx or Mx): The number of individuals that have lived during an age class. The number at risk is used to calculate Mx and Qx by dividing the number of births and deaths that occurred during an age class by the number of animals at risk of dying and reproducing during that age class. The proportion of individuals that die during an age class is calculated from the number of animals that die during an age class divided by the number of animals that were alive at the beginning of the age class (i.e.-"at risk"). Stochastic Model: A model that includes random chance and variation in model parameters (e.g. randomly select if an individual will breed). Stochastic models will produce many different outcomes each time the model is run due to this variation. Models are typically run for many iterations to fully explore the trajectory a population might take. ZooRisk is a stochastic model. Taxon Advisory Group (TAG): There are several different TAGs and each oversees a broad group of animals (e.g. Antelope TAG, Small Carnivore TAG). Each TAG consists of several programs. The TAG contains experts including studbook keepers, program leaders, the TAG chair, and other advisors. TAGs evaluate the present conditions surrounding a broad group of animals (e.g., marine mammals) and then prioritize the different species in the group for possible captive programs Population Viability Analyses for AZA Orangutan Animal Program 22