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Biological Conservation 161 (2013) 39–47
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Biological Conservation
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Habitat evaluation and population viability analysis of the last population of cao vit gibbon (Nomascus nasutus): Implications for conservation
Peng-Fei Fan a,1, Guo-Peng Ren b,1, Wei Wang c, Matthew B. Scott a, Chang-Yong Ma a, Han-Lan Fei a, ⇑ ⇑ Lin Wang b, Wen Xiao a, , Jian-Guo Zhu b, a Institute of Eastern-Himalaya Biodiversity Research, Dali University, Dali, Yunnan 671003, China b Ecology, Conservation, and Environment Center (ECEC), Kunming Institute of Zoology, Chinese Academy of Sciences, Kunming, Yunnan 650223, China c State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences (CRAES), Chaoyang, Beijing 100012, China article info abstract
Article history: The cao vit gibbon (Nomascus nasutus) is among the most endangered primates in the world. The only Received 9 December 2012 surviving population lives in a karst forest patch along the China–Vietnam border. In this study, we used Received in revised form 16 February 2013 high-resolution satellite images to evaluate the habitat quality of the gibbon in the area immediately sur- Accepted 25 February 2013 rounding the last population and predict the potential gibbon habitat. We then used Vortex to simulate population responses to changes in the habitat’s carrying capacity. Our results showed the gibbon pop- ulation is approaching the carrying capacity of their current habitat, and carrying capacity has a signifi- Keywords: cant impact on population changes. Two potential habitats were located in a forest connected to the Cao vit gibbon (Nomascus nasutus) current habitat by a narrow forest corridor, situated above an underground river. Based on the results, Habitat quality Potential habitats we recommend: (1) prohibiting agriculture and grazing activities within the current gibbon habitat; Habitat carrying capacity (2) expanding the Cao Vit Gibbon Conservation Area in order to protect potential cao vit habitats in Viet- Conservation suggestions nam; (3) protecting forest corridor that connect the current cao vit habitat to potential habitats; and (4) rehabilitating the forests currently depauperate of important food species in order to support the expan- sion of both the gibbon population and the range. This research both provides important insight into sus- taining the current gibbon population as well as suggestions for both Vietnamese and Chinese local governments planning habitat restoration at the study site. Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction it the second smallest population of any ape species worldwide after the Hainan gibbon (Zhou et al., 2005). Consequently, the The cao vit, or eastern black crested gibbon (Nomascus nasutus) cao vit gibbon has been listed as one of the World’s 25 Most Endan- is a Critically Endangered species (IUCN, 2012) with only one gered Primates (Long and Nadler, 2009). To protect the remaining known population. Historically, the species was widespread east population and its karst forest habitat, the Cao Vit Gibbon Conser- of the Red River (Hong He) in both southern China and northern vation Area in Vietnam and Bangliang Gibbon Nature Reserve in Vietnam (Geissmann et al., 2003). By the 1960s the cao vit gibbon China were established in 2007 and 2009, respectively. was considered extinct (Tan, 1985; Geissmann et al., 2003), but Previous interviews with local people indicated that the cao vit was rediscovered along Vietnam’s nothern border in 2002 (La gibbon habitat has degraded over time as a result of timber extrac- et al., 2002) and in China in 2006 (Chan et al., 2008). In 2007, a tion, fuel-wood collection, the making of charcoal, selective log- trans-boundary census of the population recorded 18 groups and ging, and agriculture encroachment (Fan et al., 2011a). While the approximately 110 individuals in the area (Le et al., 2008), making establishment of the conservation areas has reduced forest degra- dation, local inhabitants from both countries still plant corn in
⇑ Corresponding authors. Addresses: Institute of Eastern-Himalaya Biodiversity some of the valleys and some Chinese villagers continue to graze Research, Dali University, 2 Hongsheng Road, Dali, Yunnan 671003, China (W. Xiao), goats inside the Bangliang Nature Reserve. Ecology, Conservation, and Environment Center (ECEC), Kunming Institute of The mean canopy height over the site is 10.5 m, which is the Zoology, Chinese Academy of Sciences, 32 Jiaochang Donglu, Kunming, Yunnan lowest forest canopy height ever reported for gibbon habitat (Fan 650223, China. Tel. +86 871 65190776 (J.-G. Zhu). et al., 2011a). To survive in the degraded karst forest, cao vit gib- E-mail addresses: [email protected] (W. Xiao), [email protected] (J.-G. Zhu). bons consume nearly half of the tree and liana species recorded 1 These authors contributed equally to this research. (81 of the 159 species) at the site (Fan et al., 2011a). Like all other
0006-3207/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.biocon.2013.02.014 Author's personal copy
40 P.-F. Fan et al. / Biological Conservation 161 (2013) 39–47 gibbons, cao vit gibbons eat fruit when it is available, and shift to a 2. Methods leaf-dominant diet when fruit becomes less available (Fan et al., 2012). They also rest more and sleep huddled together when the 2.1. Study area temperature cools (Fan et al., 2012). To find sufficient food, cao vit gibbons occupy home ranges (130 ha, Fan et al., 2010) larger Gibbons are strict canopy dwellers and cannot disperse beyond than those of other species in south tropical rain forests (on aver- rivers, roads and other breaks in the forest canopy. We accordingly age 40 ha, Bartlett, 2007), but comparable with or smaller than the focused on the areas immediately surrounding the current cao vit Nomascus gibbons in the north (N. hainanus: 300–500 ha, Liu et al., gibbon habitat (22°49–590N, 106°220–350E). Several rivers and 1989; N. concolor: 151 ha, Fan and Jiang, 2008; N. leucogenys: ca. paved roads bisect the total research area, which can be divided 540 ha, Hu et al., 1990). Based on the estimated ca. 2000 ha of suit- into five different zones (Fig. 1). Gibbons currently only live in Zone able habitat available (Le et al., 2008), the cao vit gibbon popula- I; however, local people reported knowing of gibbons inhabiting tion is likely close to its carrying capacity. Zone IV before 2000 (Le et al., 2008). Zones I and IV are separated Remote Sensing (RS) and Geographic Information Systems (GIS) by a river, but the forests are relatively contiguous because some techniques have been widely used to evaluate habitat quality 900 m of the river is underground. (Hansen et al., 2001; Xiao et al., 2003; Zhang et al., 2010), predict potential habitat (Wang et al., 2008; Zhang et al., 2010), and plan 2.2. Forest cover mapping conservation strategies (Maiorano et al., 2006; Zhang et al., 2010). In this study, we aim to: (1) evaluate current habitat quality 2.2.1. Classification scheme and ground-truth data collection using RS and GIS techniques; (2) predict potential habitat in sur- Land cover in the study area was classified as Forest, Scrub, rounding areas and identify some ecological corridors for dis- Shrubland and Developed areas (Table 1). Between July 15 and Au- persal; and (3) use a Vortex model to simulate the sensitivity of gust 5 2010, 412 land cover polygons in China were classified and population dynamics to changes of habitat carrying capacity. delineated on satellite images with the aid of relief maps and a Glo-
Fig. 1. Study area along the China–Vietnam border. The five zones outlines in this study are divided by rivers and roads. Author's personal copy
P.-F. Fan et al. / Biological Conservation 161 (2013) 39–47 41 0 1 Table 1 12321 B C Land cover classification scheme. B C B 23432C B C Land cover Description The 5 by 5 Gaussian filter ¼ B 34543C=65 ð1Þ type B C @ 23432A 1. Forest Some trees >10 m height with a canopy cover P50% 2. Scrub Near continuous canopy of tall shrubs and dwarfed/young 12321 trees, tree canopy cover comprises <50% 3. Shrubland Mosaic of shrubs and grasses, trees few or absent We then used the hi to evaluate the quality of the gibbon hab- 4. Developed Areas of farmland, town, villages, open water and other non- itat by arbitrarily dividing the study area into the following four forested land types:
(a) high-quality habitat: hi P 80; (b) moderate-quality habitat: 60 6 hi < 80; bal Position System (GPS) receiver (Garmin eTrex). Using the same (c) low-quality habitat: 40 6 hi < 60; method, 28 land cover polygons were delineated in Vietnam from (d) non-habitat (not suitable for gibbon): hi < 40. June 15 to 26 in 2011. Half of these polygons were randomly cho- sen as validation data, and the remainders as training data for We tested whether the hi is an accurate measure of habitat classification. quality by using the field data from the extant gibbon population habitat sites, as described in the next section. 2.2.2. Remote sensing data The trans-boundary survey conducted by Fauna & Flora Interna- Two scenes of Advanced Land Observation Satellite (ALOS) tional (FFI) in September 2007 identified 18 groups using direct images, one from Panchromatic Remote-sensing Instrument for observation and listening to gibbon calls on hill tops – a widely Stereo Mapping (PRISM, 1 band, resolution = 2.5 m) and the other used method in gibbon surveys developed in 1987 by Brockelman from Advanced Visible and Near Infrared Radiometer (AVNIR-2, 4 and Ali, 1987 (Johnson et al., 2005; Buckley et al., 2006; Phoonj- bands, resolution = 10 m), both acquired on November 23, 2009, ampa and Brockelman, 2008; Fan et al., 2011b; Le et al., 2008). were used to map forest cover over the study area. After referenc- FFI directly observed 17 of the 18 gibbon populations and recorded ing with Google Earth, the ALOS PRISM image was properly geo- their group compositions (Le et al., 2008). All group locations ob- corrected. We subsequently geo-corrected the AVNIR-2 image tained from direct observations and calls were marked on a topog- band by band to the ALOS PRISM. Afterward, we used a pixel-based raphy map (1:50,000), which was used to estimate the centre of fusion method to derive a pan-sharpened image (4 bands, resolu- each group’s home range (Le et al., 2008). Referencing Appendix tion = 2.5 m) from the ALOS AVNIR-2 and PRISM images. UTM 4 in the study done by Le et al. (2008), two of the 17 locations were coordinates system (Projection: Universal Transverse Mercator, re-located according to our subsequent long-term field observa- Spheroid: WGS84, Datum: WGS84, Zone: 48N) was used in this tions. We drawn 8 concentric rings in 200 m intervals around the study. 17 gibbon locations to cover the range of the current gibbon The remote sensing data processes were conducted using Erdas (Fig. 2). Rings were labelled ring 1–8, from the innermost ring Imagine (Leica Geosystems Geospatial Imaging, LLC, Norcross, outwards. Georgia, US) and R Statistics software. If the hi is a good index for the habitat quality evaluation, the inner rings should be expected to have a higher hi than the outer rings. We conducted wilcoxon-tests between hi values for all com- 2.2.3. Land cover mapping bination of paired rings, and used the Bonferroni method in R 2.1.0 Based on the ALOS images and the training data from the field, to adjust the p-values. we produced a preliminary land cover map using the Random For- est classification algorithm (Breiman, 2001). The classification pro- cess was implemented using the RandomForest package (Liaw and 2.3. Potential habitat prediction Wiener, 2002) and Raster package (Hijmans and van Etten, 2011) in R Statistics software (2.1.0, http://www.r-project.org/). Then To predict potential habitat for the cao vit gibbon, we made we aggregated 144 pixels in the preliminary land cover map to three assumptions according to previous research and our one pixel in order to derive a land cover map at 30 m resolution, knowledge: as 2.5 m resolution was too fine for a land cover map. The accuracy Assumption 1: Potential habitat should be in close proximity to of the 30 m resolution land cover map was evaluated (producer’s high-quality habitat patches larger than 100 ha, because the home accuracy) using validation data obtained from field surveys. range size of all Nomascus gibbons (who occupy home ranges of equal or greater size to the cao vit gibbon) in northern areas is lar- 2.2.4. Habitat quality evaluation ger than 100 ha (Liu et al., 1989; Hu et al., 1990; Fan and Jiang, On the basis of the 2.5 m resolution preliminary land cover map, 2008; Fan et al., 2010). we calculated the forest pixel percentage as tree cover percentage Assumption 2: Gibbons mostly inhabit high-quality habitat, and (%tree) at 30 m resolution. Then, we performed a focal analysis can move between any two high-quality habitat patches if the dis- using a 5 by 5 Gaussian filter on the %tree to produce a habitat tance between them is less than 100 m and the two patches are quality index (hi) able to evaluate the quality of gibbon habitat. connected by at least moderate-quality habitat patches. The Gaussian filter, defined by Eq. (1), places the heaviest weight Assumption 3: Gibbons do not live in low-quality habitat or non- on the focal pixel (the pixel having the highest Gaussian value), habitat. with the weighting of neighboring pixels varying proportionately Based on these assumptions, we used the following steps to with distance from the focal pixel. predict potential gibbon habitat: The hi can be used to evaluate habitat quality for two reasons. Step 1: Select high-quality habitat patches larger than 100 ha as First, gibbons only inhabit forests and avoid all other land cover the core habitat. types; second, the possibility of site suitability for gibbons depends Step 2: Select high-quality habitat patches connected to the core not only on the forest cover percent, but also on the cover of the habitat by at most 100 m of moderate-quality habitat as additional adjacent area, both of which are taken into account in the hi. patches of core habitat. Author's personal copy
42 P.-F. Fan et al. / Biological Conservation 161 (2013) 39–47
Fig. 2. Concentric buffer rings around gibbon group locations to evaluate habitat quality (rings were labeled as ring 1 to ring 8 from inner to outer).
Step 3: Repeat step 2 until no more patches can be added to the 10 years of age, and males at around 12 years. In the absence of core habitat. other data, we used these parameters in our model. We also as- Step 4: Select moderate-quality habitat connected to high-qual- sumed that the maximum age of reproduction for gibbons is ity habitat as the marginal habitat. 30 years old (Seal, 1994). The lethal equivalent, a measure of the Step 5: Select both the core and marginal habitats as potential severity of inbreeding, was set at 3.14; in studying 40 captive ver- habitats for cao vit gibbons. tebrate populations, Ralls et al. (1988) found 3.14 lethal equiva- lents to be the median value. The average home range size of these three groups was 130 ha 2.4. Population dynamics and viability analysis (PVA) (Fan et al., 2010), which 99.8 ha (G1) and 114.2 ha (G4) was used exclusively by a single group (Fei et al., 2012). The average exclu- We used Vortex 9.99 (http://www.vortex9.org/vortex.html)to sive territory range is 107 ha for G1 and G4. Cao vit gibbons may simulate the population dynamics of the cao vit gibbon over the potentially live in smaller home ranges in well-protected forests, next 200 years (ca. 6–7 generations) assuming different habitat but such data is not available at present. We calculated the carry- carrying capacities. Vortex was developed by Lacy (1993) and has ing capacity by dividing the total habitat area by the average exclu- been widely used to analyze population viability, including gibbon sive territory range for one group, and then multiplied by the population viability (Seal, 1994; Fan and Jiang, 2007). average group size (6.0, Fan et al., 2010). We assumed no catastro- Beginning in December 2007, we monitored three Chinese cao phes, harvest/hunting, supplementation and genetic management vit gibbon groups for at least 7 days each month, recording the data in the model. All parameters are summarized in the online Appen- required to model population dynamics (Fan et al., 2010; unpub- dix 1. lished data). Over those 5 years, we recorded nine births. The in- ter-birth interval of the five females who gave birth twice was 34 months. One older female did not give birth during the 5 years. 3. Results On average, 30% of the adult females (SD = 18.2%) reproduced each year. Mortality of gibbons from age 0 to 1 was 20% (2 deaths out of 3.1. Forest cover map and accuracies 10 infants). Mortality of gibbons from age 3–4 was 20% (2 deaths of small juveniles out of 10). Mortality of gibbons at other ages was 0. A land cover map of the whole study area was produced on the We assumed that mortality was the same between sexes. basis of the ALOS images (Fig. 3). Mapping accuracies of both Forest Because of the gibbons’ longevity, it was difficult to determine and Developed areas were satisfied (>0.85), although the accura- the age at which females and males have their first offspring, as cies for the Scrub and Shrubland areas were low (Table 2). The low- well as the maximum age of reproduction. Brockelman et al. er accuracies for the transitional land cover types between forests (1998) provide the only known information on wild gibbons, and and developed areas were due to the confusion of the two land report that female Hylobates lar has their first offspring at around cover types. To correct for this, we combined Scrub and Shrubland Author's personal copy
P.-F. Fan et al. / Biological Conservation 161 (2013) 39–47 43
Fig. 3. Classification results of forest map over the study area.
Table 2 Table 3 Producer’s accuracies of the land cover classification map over study area based on The area and patch number of forest at three tier levels in each zone. 2009 satellite imageries. Zone Area of forest patches (patch number) Land cover type Validation data (n = 2353) 1.0–9.9 ha 10.0–99.9 ha >100.0 ha Total Forest Scrub Shrubland Developed I 196.4 (78) 11.7 (1) 2835.1 (1) 3043.2 (80) Forest 875 22 16 0 IV 416.8 (173) 304.8 (13) 2335.1 (4) 3101.7 (190) Scrub 111 70 301 15 III 166.3 (55) 178.2 (8) 0 344.6 (63) Shrubland 20 27 485 11 V 85.4 (29) 20.8 (2) 0 106.2 (31) Developed 0 0 61 339 II 4.7 (2) 0 0 4.7 (2) Producer’s accuracy 0.87 0.59 0.56 0.93 Total 914.5 (337) 515.6 (24) 5170.2 (5) 6600.3 (366)
into one category in the following analyses. As gibbons do not use being close to 600 m (calculated from home range size 130 ha) sug- either scrub or shrubland, pooling the categories was not expected gests that more than 90% of a groups home range is high-quality to influence the results. forest and that the hi index is a reasonable assessment of habitat In total, forests comprised 6600.3 ha of the whole 22,700 ha quality for the cao vit gibbon. study area, 93% of which (6144.9 ha) was in Zones I and IV (Table 3, There are still 3951.1 ha of high-quality habitat and 1409.6 ha Fig. 3). There were only five forest patches larger than 100 ha with of moderate-quality habitat within Zones I and IV (Fig. 4, Table 4). the total area of 5170.2 ha in Zones I and IV (Table 3). Only four patches of high-quality habitat are both larger than 100 ha and located in Zones I and IV (Table 4). 3.2. Habitat quality 3.3. Potential habitat Gibbon habitat quality was evaluated using the hi index. Our re- sults showed that habitat quality decreased significantly as dis- The total potential habitat area contains 3401.6 ha of high-qual- tance from the nearest gibbon location buffer ring increased ity habitat (Table 5) and 1125.1 ha of moderate-quality habitat. We (p < 0.001), except habitat quality within the first two rings divided them into three conservation priority areas using relatively (p = 0.641) and last two rings (p = 0.152) did not vary significantly. compacted high-quality habitats as boundaries (Fig. 5, online According to our definition of high-quality habitat (hi P 80), more Appendix 2). The first conservation priority area is the only area than 97% of the first ring is high-quality habitat, and more than currently inhabited by gibbons, comprising a total 2216.7 ha 95%, 90%, 74%, 50% of the successive four rings are high-quality (79.9%) of high-quality habitat. The second priority area is con- habitat, respectively. The home range radius of a single group nected by a narrow strip (width = 900 m) of forest to the first pri- Author's personal copy
44 P.-F. Fan et al. / Biological Conservation 161 (2013) 39–47
Fig. 4. Habitat quality over the five zones in the study area.
sufficient habitat for 20 groups (or 120 individuals). The first prior- Table 4 ity area (2775.3 ha, Table 6) could support 26 groups or 156 indi- Area and patch number of different habitat quality within Zone I & IV. viduals if the area was rehabilitated to support gibbons. Quality level Area (patch number) Total Furthermore, if gibbons could disperse to the second priority area, 1.0–9.9 ha 10.0–99.9 ha >100.0 ha and all the first and second priority areas were rehabilitated in or- der to support gibbons, then the area could support 37 groups or High 274.9 (82) 605.9 (17) 3080.3 (4) 3951.1 (102) Moderate 1074.7 (435) 334.9 (22) 0 1409.6 (457) 222 individuals. If gibbons could further disperse to the third pri- Low 1094.9 (471) 121.8 (10) 0 1216.7 (481) ority area, then the area could possibly support 48 groups or 288 individuals. Without catastrophes and hunting, habitat capacity has a significant impact on population growth. In each of these sit-
Table 5 uations, this population could reach carrying capacity within Area and patch number of high-quality habitat within each conservation priority 40 years (Fig. 6). areas.
Priority area Area (patch number) Total 4. Discussion 1.0–9.9 ha 10.0–99.9 ha >100.0 ha 1st 8.1 (3) 31.8 (2) 2176.8 (1) 2216.7 (6) Although the cao vit gibbons from the study site live in a low 2nd 3.5 (2) 87.5 (3) 590.6 (1) 681.6 (6) karst forest (Fan et al., 2011a), gibbons are canopy dwellers and 3rd 21.8 (7) 170.8 (4) 310.7 (2) 503.4 (13) tend to avoid lower forest stratum (Gittins, 1983; Cannon and Total 33.5 (12) 290.0 (9) 3078.1 (4) 3401.6 (25) Leighton, 1994; Hasan et al., 2007; Fan et al., 2009; Fan et al., 2013). During the 2096 h spent observing the behavior of three cao vit gibbon groups (Fan et al., 2013), we observed only one case ority area, and the forest is above an underground river. The second in which a juvenile male walked on a stone for few seconds. To and third conservation priority areas are separated by a village and date, no study has reported the ability of gibbons to disperse across the surrounding farmland. The percentage of high-quality habitat rivers or roads, suggesting that the current population of cao vit within the second and third priority areas was 57.8% and 41.8%, gibbon cannot naturally disperse out of the study area. respectively. Areas of high-quality habitat and the types of land In a broader sense, we noted that for canopy dwellers, like the cover are summarized in Tables 5 and 6. gibbon, forest canopy cover could be used as a proxy to evaluate habitat quality. Our results, based on the assumption that canopy 3.4. Population viability analysis dwellers depend on the canopy cover of not only their habitat but also that of adjacent areas, showed that the habitat quality in- Excluding patches smaller than 100 ha, the high-quality forest dex (hi) is useful for studying the habitat of cao vit gibbon, and in the first priority area was 2176.8 ha (Table 5), which can provide could potentially be applied to other canopy dwellers. Author's personal copy
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Fig. 5. Three suggested priority conservation areas for the cao vit gibbon.
Table 6 Area (ha) and patch number of different land cover types within each conservation feasible and effective way to conserve and grow the cao vit gibbon priority areas. population.
Priority area Area (patch number) Total We identified two potential habitats (the 2nd and 3rd priority areas) in Zone IV. Only a narrow forest corridor (900 m in length) Forest Scrub/Shrubland Developed above an underground river connects the current habitat in the 1st 2469.7 (15) 274.3 (540) 31.3 (119) 2775.3 1st conservation area and the 2nd priority area. If this corridor 2nd 900.6 (21) 220.3 (372) 58.3 (125) 1179.2 were destroyed, the gibbons could not disperse naturally (Fig. 5). 3rd 796.1 (29) 268.2 (509) 138.6 (253) 1202.9 Total 4166.4 (65) 726.9 (1421) 228.2 (497) 5157.4 Compared with the 1st priority area, the 2nd and 3rd priority areas may not be able to support gibbon populations at present because the percentage of high-quality forests are lower, forests are more As the last refuge of the cao vit gibbon, the Zone I habitat is inte- fragmented, and there are more farmlands (Tables 5 and 6, gral to conservation efforts. However, human disturbances on both Fig. 2). Unfortunately, we were unable to set plant plots in the sides of the border continue to frustrate government efforts at con- 2nd and 3rd priority areas this time to conduct a detailed compar- serving gibbon habitat (Fan et al., 2011a), and subsequently raising ison of the forest quality (forest structure and plant diversity) with the carrying capacity beyond 20 groups. The total area of Zone I is the current gibbon habitat (1st priority area), as they are primarily 3043.2 ha (Table 3), and the total potential gibbon habitat is located in Vietnam. Likewise, the presence of villages and farm- 2775.3 ha in the first priority area (Table 6), 2176.8 ha of which lands in or near the potential gibbon habitats disconnected the are high-quality patches larger than or equal to 100 ha (Table 5). 2nd and 3rd priority areas and threaten the possibility of establish- This area has a carrying capacity of approximately 20 groups. In ing them as future cao vit habitat. the 2007 trans-boundary census, 18 groups were recorded (Le Zones II, III and V are separated from Zones I and IV by roads et al., 2008), indicating the current population is nearing the 20- and rivers. These zones were generally more degraded than Zones group carrying capacity of the current habitat. This hypothesis is I and IV with no forest patches larger than 100 ha recorded (Ta- further supported through direct observation; no new group has ble 3). Consequently, we concluded that Zones II, III and V should formed since observation in China after 2009, despite observing 5 have a lower priority for future gibbon conservation. floating females and upwards of 6 floating males in the area over a PVA shows that the current population could reach carrying 4-year span. If the entire area of the first priority area were up- capacity within 40 years in any situations barring catastrophes graded to a high-quality habitat, then the carrying capacity would and hunting. Since the population was rediscovered in 2002, hunt- increase to 26 groups. PVA demonstrated that this population will ing has not been reported in either China or Vietnam. Forest fires likely reach carrying capacity in 15 years. Moreover, transforming are thought to be a serious threat in some gibbon habitat (Cheyne, all the first priority area into high-quality habitat is the most 2007), but none have been recorded in our study site for more than Author's personal copy
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Fig. 6. Population dynamics of the cao vit gibbon under four situations with the carrying capacity (K) set at 126 (current habitat capacity), 156 (all area could be used in priority forest 1), 222 (all area could be used in priority forest 1 and 2), and 288 (all area could be used in priority forest 1, 2 and 3) individuals.
30 years (data not published, personal communication from our Natural Science Foundation of China (#30900169, 31272327), and field guides). Because gibbons occupy home ranges used almost Fauna and Flora International (FFI). Idea Wild provided equipment exclusively by the resident group (Bartlett, 2007), the breeding of for this research. All research methods adhered to the appropriate females is thought to be independent of group densities. However, Chinese legal requirements. We would like to thank the staffs of Ban- mortality rates of adults and sub-adults were higher in populations gliang Nature Reserve in China, Cao Vit Gibbon Conservation Area in close to carrying capacity (Brockelman et al., 1998). In this re- Vietnam, and FFI Vietnam for their much needed support during our search, we did not consider the effects of population density on field work. We are also grateful to Dr. Li Li, Mr. Paul Insu-Cao and the gibbon mortality rates. While we acknowledge the limitations of two anonymous reviewers for their helpful comments. the parameters of the model, PVAs provide us with some crucial information, namely that habitat carrying capacity is the most Appendix A. Supplementary material important factor limiting gibbon population expansion. In summary, the last remaining population of cao vit gibbon is Supplementary data associated with this article can be found, in nearing its carrying capacity in the current remaining forest patch the online version, at http://dx.doi.org/10.1016/j.bio- (Zone 1). There are two potential areas for the gibbon’s future dis- con.2013.02.014. These data include Google maps of the most persal in the adjacent Zone IV. Currently, the Vietnamese govern- important areas described in this article. ment has not protected these two potential habitats. However, high-quality habitat within these two potential areas is more frag- mented than the current gibbon habitat in Zone I. 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