In this discussion, you will review and summarize information of a study in which researchers reported estimations of population parameters of their interest. Article below:Estimating the population density of Mongolian gazelles Procapragutturosa by driving long-distance transects
Estimating the population density of Mongolian gazelles Procapra gutturosa by driving long-distance transects In this discussion, you will review and summarize information of a study in which researchers reported estimations of population parameters of their interest. Article below: Estimating the population density of Mongolian gazelles Procapra gutturosa by driving long-distance transects Kirk A. Olson, Todd K. Fuller, George B. Schaller, Daria Odonkhuu and Martyn G. Murray In your initial discussion post (due Wednesday): (1) Report the objective of the study and study site (50-100 words), (2) Report measured variables and the data collection method (50-100 words) (3) Select one variable and report the point estimate and interval estimate for the variable. (4) Interpret the confidence interval you have reported above. Do you think the reported interval is narrow or wide for the variable? (50-100 words) (5) Provide a concise conclusion of the study discussed by the authors. Then describe your thoughts on why the estimations of the variable are important in the study. (50-100 words) Oryx Vol 39 No 2 April 2005 © 2005 FFI, Oryx, 39(2), 164–169 doi:10.1017/S0030605305000402 Printed in the United Kingdom164 Estimating the population density of Mongolian gazelles Procapra gutturosa by driving long-distance transects Kirk A. Olson, Todd K. Fuller, George B. Schaller, Daria Odonkhuu and Martyn G. Murray varied from 10.7 gazelles km−2 in spring to 11.5 gazelles km−2 in autumn, with total population estimates of 803,820 (483,790–1,330,100 95% confidence interval) and 870,625 (499,432–1,491,278 95% confidence interval), respectively. Confidence limits were wide, and to obtain a coefficient of variation of 20%, transect lengths would need to be extended three- to four-fold. Until more efficient means for conducting population surveys can be implemented, driving long-distance transects, com- bined with distance analysis, seem to provide the best quantitative estimate of Mongolian gazelle populations. Keywords Density, distance sampling, estimate, gazelles, line transects, Mongolia, population, Procapra gutturosa. Abstract Despite ag75% reduction in the geographic range of Mongolian gazelles Procapra gutturosa over the past 50 years, the species is still recognized as the most numerous large grassland herbivore in Asia. Its actual population size, however, is still disputed, and we there- fore estimated its numbers in an 80,000 km2 area in the eastern steppe of Mongolia by driving long-distance (1,200–1,400 km) transect surveys during spring and autumn 2000–2002. Quantitative estimates of gazelle numbers are essential for understanding the causes of changes in the population, and thus devising conserva- tion strategies to assure its long-term viability. Observed herds ranged in size from 1–4,000; among surveys, median herd sizes varied from 14–42. Density estimates Kirk A. Olson Department of Natural Resources Conservation, 160 Holdsworth Way, University of Massachusetts, Amherst, MA 01003 9285, USA, and Wildlife Conservation Society, 2300 Southern Boulevard, Bronx, NY 10460, USA. Todd K. Fuller (Corresponding author) Department of Natural Resources Conservation, 160 Holdsworth Way, University of Massachusetts, Amherst, MA 01003 9285, USA. E-mail
[email protected] George B. Schaller Wildlife Conservation Society, 2300 Southern Boulevard, Bronx, NY 10460, USA. Daria Odonkhuu Ecology Department, National University of Mongolia, Ikh Surguuliin Gudamj, Building 2, Ulaanbaatar, Mongolia. Martyn G. Murray Institute of Cell, Animal, and Population Biology, Ashworth Labs, West Mains Road, Edinburgh, EH9 3JT, UK. Received 21 May 2004. Revision requested 2 July 2004. Accepted 3 November 2004. Introduction In the past 50 years the range of the Mongolian gazelle Procapra gutturosa was reduced by up to 75% in Mongolia (from 780,000 km2 in the 1940s to as low as 190,000 km2 in 1997) and Inner Mongolia, China (from 300,000 km2 during 1950–1970 to<75,000 km2 in 1995) and virtually eliminated in russia (bannikov et al., 1961; lhagvasuren & milner-gulland, 1997; xiaoming et al., 1997; jiang et al., 1998). despite this, the species is still recognized as ‘one of asia’s largest remaining wildlife populations’ (finch, 1996). for centuries mongolian pastoralists have utilized mongolian gazelles as a supplement to their diet, and for much of the past century the population has been harvested for commercial purposes (milner-gulland & lhagvasuren, 1998; reading et al., 1998; sampildendev, 2000). recently, a moratorium was placed on large-scale harvesting for export, but widespread poaching and hunting for local markets still occurs (scharf & enkhbold, 2002). despite the cultural and economic importance of this species its actual population size has been the subject of controversy and contradictions; partial or total population estimates have ranged from as few as 180,000 to as many as 2,670,000 (milner-gulland & lhagvasuren, 1998). currently there is no consistent standardized moni- toring programme for the mongolian gazelle. a severe population decline in the future due to a disease out- break (schaller & lhagvasuren, 1998), massive illegal harvest and subsequent reproductive collapse (milner- gulland et al., 2003), or severe winter weather (lhagvasuren & milner-gulland, 1997), could: (1) result in a cascading decrease in ecosystem functionality and loss of biodiversity, (2) have a negative impact on tradi- tional subsistence hunting practices, and (3) confound the setting of hunting quotas for what may seem to be a sustainable harvest for promoting conservation. without regular, quantitative assessment of the population, the conservation of this species cannot be assured. conse- quently, we attempted to estimate the population size https://www.cambridge.org/core/terms. https://doi.org/10.1017/s0030605305000402 downloaded from https://www.cambridge.org/core. ip address: 69.137.173.208, on 09 jul 2020 at 16:58:53, subject to the cambridge core terms of use, available at https://www.cambridge.org/core/terms https://doi.org/10.1017/s0030605305000402 https://www.cambridge.org/core 165 © 2005 ffi, oryx, 39(2), 164–169 density estimates of mongolian gazelles of mongolian gazelles in part of the eastern steppe by conducting vehicle transect surveys over a period of several years. we also aimed to assess the rigour needed to identify significant population changes over time. study area at c. 250,000 km2 mongolia’s eastern steppe is one of the largest intact grazing ecosystems in the world (finch, 1996). topography of the steppe is level to undulating over elevations of 600–1,100 m. one major river (kherlen river) runs from west to east through the centre of the steppe (fig. 1). we concentrated survey efforts in an 80,000 km2 region in south-eastern dornod aimag and eastern sukhbaatar aimag. this region is a focal point for development interests such as roads and oil fields (pentilla, 1994; asian development bank, 2002). steppe vegetation is dominated by grasses such as stipa spp., cleistogenes spp. and leymus spp., forbs, particularly artemisia spp., allium spp. and astragulus spp., and sedges carex spp. for an overview of the vegetation of the eastern steppe, see gunin et al. (2000) and jigjidsuren & johnson (2003). potential predators of gazelles are wolves canis lupus, and raptors such as steppe eagles aquila rapax and golden eagles aquila chrysaetos. methods the study area was divided into seven strips, each 60 km wide and 50–300 km long (fig. 1). starting and stopping points were chinese-mongolian border fences or major road crossings following the kherlen river. transects were driven from north to south. using a global positioning system (gps), we kept as close to the transect line as possible. conditions were almost always favourable to driving straight lines. four observers participated in all surveys. we attempted to maintain a constant speed of 25–35 km hr−1. surveys were con- ducted in the last half of may and the early part of june in spring 2000 and 2002, in late september and early october in autumn 2001, and in late august and early september in autumn 2002; each survey lasted 12–18 days and covered 1,186–1,398 km (table 1). when we sighted gazelles, we attempted to count them with spotting scopes or binoculars before they detected the vehicle and ran out of sight. using a range- finder, distance measurements were made following the protocol outlined in buckland et al. (2001) for sampling objects in clusters. group size was estimated by counting individual animals or groups. distance sampling analysis using the software distance (thomas et al., 2003) was used to estimate gazelle densi- ties from line transects. data preparation and analysis followed the general guidelines of buckland et al. (2001). in order to minimize the effects of measurement error, herd locations were placed into intervals for final analysis. final model selection was chosen based on the lowest aic (akaike’s information criterion) value (buckland et al., 2001). to minimize the effects of any size bias in detection of clusters as they approached w, maximum sighting distance (drummer & mcdonald, 1987), we regressed ln (cluster size) against estimated g(x) (detection probability) (buckland et al., 2001). fig. 1 study area (shaded) and locations of transects (t1–t6, dashed lines) used to survey mongolian gazelles in eastern steppe habitat in mongolia. the inset map shows the position of the main figure within mongolia. https://www.cambridge.org/core/terms. https://doi.org/10.1017/s0030605305000402 downloaded from https://www.cambridge.org/core. ip address: 69.137.173.208, on 09 jul 2020 at 16:58:53, subject to the cambridge core terms of use, available at https://www.cambridge.org/core/terms https://doi.org/10.1017/s0030605305000402 https://www.cambridge.org/core 166 © 2005 ffi, oryx, 39(2), 164–169 k. a. olson et al. we used a z-test to determine if a change in density could be detected between surveys (buckland et al., 2001). to increase precision of the estimates data for spring and autumn were combined and analysed accord- ing to the above procedure. we also used distance to estimate density based on an 800-m strip (400 m each side), using the uniform key with no adjustments, for comparison between distance sampling analyses and strip transect analyses, the latter being simpler to analyse. results we counted 110–174 groups of 1–4,000 gazelles during the surveys; among years, mean group size was 96–213 and median group size 14–42 (table 1). for distance sampling analyses, selected strip widths varied between 601 and 1,499 m, and uniform-cosine or half normal- cosine models provided the best fit at the centre lines of the transects (i.e. where observability is assumed to be 1.0; table 2). the contribution of small clusters to the overall estimated population size was minimal (table 3). in the 80,000 km2 survey area, densities estimated from distance sampling analyses in spring were 9.9–11.5 gazelles km−2, averaging 10.7 gazelles km−2, giving a point estimate of c. 800,000 (table 4). densities in autumn were 5.4–15.8 gazelles km−2, averaging 11.5 gazelles km−2, or c. 870,000 gazelles in total, similar to the spring estimate km2="" in="" 1995)="" and="" virtually="" eliminated="" in="" russia="" (bannikov="" et="" al.,="" 1961;="" lhagvasuren="" &="" milner-gulland,="" 1997;="" xiaoming="" et="" al.,="" 1997;="" jiang="" et="" al.,="" 1998).="" despite="" this,="" the="" species="" is="" still="" recognized="" as="" ‘one="" of="" asia’s="" largest="" remaining="" wildlife="" populations’="" (finch,="" 1996).="" for="" centuries="" mongolian="" pastoralists="" have="" utilized="" mongolian="" gazelles="" as="" a="" supplement="" to="" their="" diet,="" and="" for="" much="" of="" the="" past="" century="" the="" population="" has="" been="" harvested="" for="" commercial="" purposes="" (milner-gulland="" &="" lhagvasuren,="" 1998;="" reading="" et="" al.,="" 1998;="" sampildendev,="" 2000).="" recently,="" a="" moratorium="" was="" placed="" on="" large-scale="" harvesting="" for="" export,="" but="" widespread="" poaching="" and="" hunting="" for="" local="" markets="" still="" occurs="" (scharf="" &="" enkhbold,="" 2002).="" despite="" the="" cultural="" and="" economic="" importance="" of="" this="" species="" its="" actual="" population="" size="" has="" been="" the="" subject="" of="" controversy="" and="" contradictions;="" partial="" or="" total="" population="" estimates="" have="" ranged="" from="" as="" few="" as="" 180,000="" to="" as="" many="" as="" 2,670,000="" (milner-gulland="" &="" lhagvasuren,="" 1998).="" currently="" there="" is="" no="" consistent="" standardized="" moni-="" toring="" programme="" for="" the="" mongolian="" gazelle.="" a="" severe="" population="" decline="" in="" the="" future="" due="" to="" a="" disease="" out-="" break="" (schaller="" &="" lhagvasuren,="" 1998),="" massive="" illegal="" harvest="" and="" subsequent="" reproductive="" collapse="" (milner-="" gulland="" et="" al.,="" 2003),="" or="" severe="" winter="" weather="" (lhagvasuren="" &="" milner-gulland,="" 1997),="" could:="" (1)="" result="" in="" a="" cascading="" decrease="" in="" ecosystem="" functionality="" and="" loss="" of="" biodiversity,="" (2)="" have="" a="" negative="" impact="" on="" tradi-="" tional="" subsistence="" hunting="" practices,="" and="" (3)="" confound="" the="" setting="" of="" hunting="" quotas="" for="" what="" may="" seem="" to="" be="" a="" sustainable="" harvest="" for="" promoting="" conservation.="" without="" regular,="" quantitative="" assessment="" of="" the="" population,="" the="" conservation="" of="" this="" species="" cannot="" be="" assured.="" conse-="" quently,="" we="" attempted="" to="" estimate="" the="" population="" size="" https://www.cambridge.org/core/terms.="" https://doi.org/10.1017/s0030605305000402="" downloaded="" from="" https://www.cambridge.org/core.="" ip="" address:="" 69.137.173.208,="" on="" 09="" jul="" 2020="" at="" 16:58:53,="" subject="" to="" the="" cambridge="" core="" terms="" of="" use,="" available="" at="" https://www.cambridge.org/core/terms="" https://doi.org/10.1017/s0030605305000402="" https://www.cambridge.org/core="" 165="" ©="" 2005="" ffi,="" oryx,="" 39(2),="" 164–169="" density="" estimates="" of="" mongolian="" gazelles="" of="" mongolian="" gazelles="" in="" part="" of="" the="" eastern="" steppe="" by="" conducting="" vehicle="" transect="" surveys="" over="" a="" period="" of="" several="" years.="" we="" also="" aimed="" to="" assess="" the="" rigour="" needed="" to="" identify="" significant="" population="" changes="" over="" time.="" study="" area="" at="" c.="" 250,000="" km2="" mongolia’s="" eastern="" steppe="" is="" one="" of="" the="" largest="" intact="" grazing="" ecosystems="" in="" the="" world="" (finch,="" 1996).="" topography="" of="" the="" steppe="" is="" level="" to="" undulating="" over="" elevations="" of="" 600–1,100="" m.="" one="" major="" river="" (kherlen="" river)="" runs="" from="" west="" to="" east="" through="" the="" centre="" of="" the="" steppe="" (fig.="" 1).="" we="" concentrated="" survey="" efforts="" in="" an="" 80,000="" km2="" region="" in="" south-eastern="" dornod="" aimag="" and="" eastern="" sukhbaatar="" aimag.="" this="" region="" is="" a="" focal="" point="" for="" development="" interests="" such="" as="" roads="" and="" oil="" fields="" (pentilla,="" 1994;="" asian="" development="" bank,="" 2002).="" steppe="" vegetation="" is="" dominated="" by="" grasses="" such="" as="" stipa="" spp.,="" cleistogenes="" spp.="" and="" leymus="" spp.,="" forbs,="" particularly="" artemisia="" spp.,="" allium="" spp.="" and="" astragulus="" spp.,="" and="" sedges="" carex="" spp.="" for="" an="" overview="" of="" the="" vegetation="" of="" the="" eastern="" steppe,="" see="" gunin="" et="" al.="" (2000)="" and="" jigjidsuren="" &="" johnson="" (2003).="" potential="" predators="" of="" gazelles="" are="" wolves="" canis="" lupus,="" and="" raptors="" such="" as="" steppe="" eagles="" aquila="" rapax="" and="" golden="" eagles="" aquila="" chrysaetos.="" methods="" the="" study="" area="" was="" divided="" into="" seven="" strips,="" each="" 60="" km="" wide="" and="" 50–300="" km="" long="" (fig.="" 1).="" starting="" and="" stopping="" points="" were="" chinese-mongolian="" border="" fences="" or="" major="" road="" crossings="" following="" the="" kherlen="" river.="" transects="" were="" driven="" from="" north="" to="" south.="" using="" a="" global="" positioning="" system="" (gps),="" we="" kept="" as="" close="" to="" the="" transect="" line="" as="" possible.="" conditions="" were="" almost="" always="" favourable="" to="" driving="" straight="" lines.="" four="" observers="" participated="" in="" all="" surveys.="" we="" attempted="" to="" maintain="" a="" constant="" speed="" of="" 25–35="" km="" hr−1.="" surveys="" were="" con-="" ducted="" in="" the="" last="" half="" of="" may="" and="" the="" early="" part="" of="" june="" in="" spring="" 2000="" and="" 2002,="" in="" late="" september="" and="" early="" october="" in="" autumn="" 2001,="" and="" in="" late="" august="" and="" early="" september="" in="" autumn="" 2002;="" each="" survey="" lasted="" 12–18="" days="" and="" covered="" 1,186–1,398="" km="" (table="" 1).="" when="" we="" sighted="" gazelles,="" we="" attempted="" to="" count="" them="" with="" spotting="" scopes="" or="" binoculars="" before="" they="" detected="" the="" vehicle="" and="" ran="" out="" of="" sight.="" using="" a="" range-="" finder,="" distance="" measurements="" were="" made="" following="" the="" protocol="" outlined="" in="" buckland="" et="" al.="" (2001)="" for="" sampling="" objects="" in="" clusters.="" group="" size="" was="" estimated="" by="" counting="" individual="" animals="" or="" groups.="" distance="" sampling="" analysis="" using="" the="" software="" distance="" (thomas="" et="" al.,="" 2003)="" was="" used="" to="" estimate="" gazelle="" densi-="" ties="" from="" line="" transects.="" data="" preparation="" and="" analysis="" followed="" the="" general="" guidelines="" of="" buckland="" et="" al.="" (2001).="" in="" order="" to="" minimize="" the="" effects="" of="" measurement="" error,="" herd="" locations="" were="" placed="" into="" intervals="" for="" final="" analysis.="" final="" model="" selection="" was="" chosen="" based="" on="" the="" lowest="" aic="" (akaike’s="" information="" criterion)="" value="" (buckland="" et="" al.,="" 2001).="" to="" minimize="" the="" effects="" of="" any="" size="" bias="" in="" detection="" of="" clusters="" as="" they="" approached="" w,="" maximum="" sighting="" distance="" (drummer="" &="" mcdonald,="" 1987),="" we="" regressed="" ln="" (cluster="" size)="" against="" estimated="" g(x)="" (detection="" probability)="" (buckland="" et="" al.,="" 2001).="" fig.="" 1="" study="" area="" (shaded)="" and="" locations="" of="" transects="" (t1–t6,="" dashed="" lines)="" used="" to="" survey="" mongolian="" gazelles="" in="" eastern="" steppe="" habitat="" in="" mongolia.="" the="" inset="" map="" shows="" the="" position="" of="" the="" main="" figure="" within="" mongolia.="" https://www.cambridge.org/core/terms.="" https://doi.org/10.1017/s0030605305000402="" downloaded="" from="" https://www.cambridge.org/core.="" ip="" address:="" 69.137.173.208,="" on="" 09="" jul="" 2020="" at="" 16:58:53,="" subject="" to="" the="" cambridge="" core="" terms="" of="" use,="" available="" at="" https://www.cambridge.org/core/terms="" https://doi.org/10.1017/s0030605305000402="" https://www.cambridge.org/core="" 166="" ©="" 2005="" ffi,="" oryx,="" 39(2),="" 164–169="" k.="" a.="" olson="" et="" al.="" we="" used="" a="" z-test="" to="" determine="" if="" a="" change="" in="" density="" could="" be="" detected="" between="" surveys="" (buckland="" et="" al.,="" 2001).="" to="" increase="" precision="" of="" the="" estimates="" data="" for="" spring="" and="" autumn="" were="" combined="" and="" analysed="" accord-="" ing="" to="" the="" above="" procedure.="" we="" also="" used="" distance="" to="" estimate="" density="" based="" on="" an="" 800-m="" strip="" (400="" m="" each="" side),="" using="" the="" uniform="" key="" with="" no="" adjustments,="" for="" comparison="" between="" distance="" sampling="" analyses="" and="" strip="" transect="" analyses,="" the="" latter="" being="" simpler="" to="" analyse.="" results="" we="" counted="" 110–174="" groups="" of="" 1–4,000="" gazelles="" during="" the="" surveys;="" among="" years,="" mean="" group="" size="" was="" 96–213="" and="" median="" group="" size="" 14–42="" (table="" 1).="" for="" distance="" sampling="" analyses,="" selected="" strip="" widths="" varied="" between="" 601="" and="" 1,499="" m,="" and="" uniform-cosine="" or="" half="" normal-="" cosine="" models="" provided="" the="" best="" fit="" at="" the="" centre="" lines="" of="" the="" transects="" (i.e.="" where="" observability="" is="" assumed="" to="" be="" 1.0;="" table="" 2).="" the="" contribution="" of="" small="" clusters="" to="" the="" overall="" estimated="" population="" size="" was="" minimal="" (table="" 3).="" in="" the="" 80,000="" km2="" survey="" area,="" densities="" estimated="" from="" distance="" sampling="" analyses="" in="" spring="" were="" 9.9–11.5="" gazelles="" km−2,="" averaging="" 10.7="" gazelles="" km−2,="" giving="" a="" point="" estimate="" of="" c.="" 800,000="" (table="" 4).="" densities="" in="" autumn="" were="" 5.4–15.8="" gazelles="" km−2,="" averaging="" 11.5="" gazelles="" km−2,="" or="" c.="" 870,000="" gazelles="" in="" total,="" similar="" to="" the="" spring="">