Overview, Critical Assessment, and Conservation Implications of Koala Distribution and Abundance

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Overview, Critical Assessment, and Conservation Implications of Koala Distribution and Abundance
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    619  Conservation Biology, Pages 619–628 Volume 14, No. 3, June 2000  Overview, Critical Assessment, and Conservation Implications of Koala Distribution and Abundance   ALISTAIR MELZER,* FRANK CARRICK,†, PETER MENKHORST,‡ DANIEL LUNNEY,§  AND BARBARA ST. JOHN**  *Koala Research Centre of Central Queensland, Central Queensland University, Rockhampton, QLD 4702,  Australia, email a.melzer@cqu.edu.au†Koala Study Centre, Department of Zoology, University of Queensland, QLD 4072, Australia‡Flora and Fauna Branch, Department of Natural Resources and the Environment, P.O. Box 41, East Melbourne 3002, Australia§New South Wales, National Parks and Wildlife Service, P.O. Box 1967, Hurstville, NSW 2220, Australia**Department of Environment, Heritage and Absrcinal Affairs, P.O. Box 1047, Adelaide, SA 5001, Australia   Abstract:   Regional and national surveys provide a broadscale description of the koala’s present distribution in Australia. A detailed understanding of its distribution is precluded, however, by past and continuing land clear- ing across large parts of the koala’s range. Koala population density increased in some regions during the late1800s and then declined dramatically in the early 1900s. The decline was associated with habitat loss, hunting,disease, fire, and drought. Declines are continuing in Queensland and New South Wales. In contrast, dense koala populations in habitat isolates in Victoria and South Australia are managed to reduce population size and browse damage. Current understanding of koala distribution and abundance suggests that the species does not meet Australian criteria as endangered or vulnerable fauna. Its conservation status needs to be reviewed, how- ever, in light of the extensive land clearing in New South Wales and Queensland since the last (1980s) broadscale surveys. Consequently, we recommend that broadacre clearing be curtailed in New South Wales and Queensland and that regular, comprehensive, standardized, national koala surveys be undertaken. Given the fragmentationof koala habitat and regional differences in the status of the koala, we recommended that studies on regional variation in the koala be intensified and that koala ecology in fragmented and naturally restricted habitats bedeveloped. More generally, the National Koala Conservation Strategy should be implemented.   Visión General, Evaluación Crítica y Consecuencias para la Conservación de la Distribución y Abundancia del Koala  Resumen:   Los reconocimientos regionales y nacionales proveen una descripción amplia de la distribuciónactual del koala en Australia. Sin embargo, el reconocimiento detallado de su distribución ha sido impedido por prácticas de clareo actuales y del pasado en grandes extensiones del rango de distribución del koala. Ladensidad poblacional del koala incrementó en algunas regiones a finales del siglo dieciocho y disminuyódramáticamente a comienzos del siglo diecinueve. Esta disminución estuvo asociada con la pérdida del hábi- tat, la caza, enfermedades, incendios y sequías. Esta disminución continúa en Queensland (QLD) y NewSouth Wales (NSW). En contraste, las poblaciones densas de koalas en hábitats aislados en Victoria y Austra- lia del Sur son manejadas para reducir el tamaño poblacional y el daño por ramoneo. El conocimiento ac- tual de la distribución y abundancia del koala sugiere que la especie no reúne los criterios australianos para ser considerada como fauna amenazada o vulnerable. Sin embargo, este estado de conservación necesita ser revisado debido al clareo extensivo de tierras en NSW y QLD desde los últimos reconocimientos a gran escalarealizados durante los años ochenta. Por consiguiente, recomendamos que se restrinja el clareo extendido detierras en NSW y QLD, y que se lleven a cabo reconocimientos de koalas regulares, integrales y estandariza- dos a nivel nacional. Dada la fragmentación del hábitat del koala y las diferencias regionales en el estado deconservación del koala, recomendamos que se intensifiquen los estudios de la variación regional del koala yque se desarrollen estudios ecológicos del koala en hábitats fragmentados y naturalmente restringidos. Entérminos generales, se debe implementar la Estrategia Nacional de Conservación del Koala.   Paper submitted August 23, 1999; revised manuscript accepted December 30, 1999.    620    Koala Distribution and AbundanceMelzer et al.  Conservation Biology  Volume 14, No. 3, June 2000  Introduction  Koalas are folivorous arboreal marsupials that are natu-rally restricted to eastern Australian forests and wood-lands that contain  Eucalyptus  species. They are pro-tected in all states and territories. Koala conservationstatus is defined by separate legislation in each state and varies across the animal’s range, reflecting regional dif-ferences in perceived threats to koalas and their habitat.In Queensland, the koala is listed as “common wildlife”under the Queensland Nature Conservation Act 1992; inNew South Wales as “vulnerable” under the ThreatenedSpecies Conservation Act 1995; in South Australia as“rare” under the National Parks and Wildlife Act 1972. In Victoria the koala has no separate designation but is“protected wildlife” along with all native vertebrates un-der the Wildlife Act 1975.The koala’s range has declined since European settle-ment (e.g., for New South Wales, Phillips 1990; Reed & Lunney 1990; nationally, Martin & Handasyde 1995), andpopulations continue to decline in many areas (Maxwellet al. 1996; Australian and New Zealand Environmentand Conservation Council [ANZECC] 1998). Neverthe-less, koalas are widespread and locally abundant and notconsidered vulnerable or endangered under the com-monwealth Endangered Species Protection Act 1992.Koalas are listed as near threatened in the National Ac-tion Plan for Monotremes and Marsupials—one category below vulnerable (Maxwell et al. 1996).Some nongovernmental organizations have disagreed(Total Environment Centre 1983). In 1996 the AustralianKoala Foundation (Maxwell et al. 1996) made unsuc-cessful submissions to the commonwealth governmentfor vulnerable  status under the Endangered Species Pro-tection Act 1992. Australians For Animals (unpublisheddocument) is seeking to have the koala included on theU.S. Endangered Species list. We examined current pop-ulation size and distribution because an accurate assess-ment of conservation status depends on this informa-tion.  Koala Distribution and Abundance  Historic  The extent of the koala’s range at the time of Europeancontact has not been established accurately. The first re-corded sighting was in 1798, and koalas were rarely re-ported up to about 1830 (Phillips 1990). Gould (1863)found the species difficult to locate and restricted todense and tall  Eucalyptus  forests. By 1870 they were be-ing sighted in lowland, open eucalypt forests and wood-lands (Lee & Martin 1988; Phillips 1990).By the 1890s the koala was common in much of itsrange (Phillips 1990). The apparent increase in regionalpopulation density may have been due either to expand-ing European settlement and the increasing visibility of koalas or to relief from Absrcinal hunting pressure. InQueensland at least, the removal of Absrcinal fire re-gimes in conjunction with European grazing and land-management practices (prior to the introduction of broadacre clearing) may have increased the extent anddensity of eucalypt forests and woodlands (Burrows1996). This may have increased available habitat andperhaps facilitated the expansion of koala distributionand numbers.The density of koalas in the 1890s supported an inten-sive hunting industry. Between 1890 and the early 1900s, several million skins were exported (Phillips 1990).Hunting, clearing, wildfire, and disease epidemics fromthe late 1880s through the early 1930s (Finlayson 1934;Parris 1948; Warneke 1978; Lunney & Leary 1988; Gor-don et al. 1990  a  ; Lunney et al. 1990; Phillips 1990; Gor-don 1996) contributed to population crashes. A major reduction in distribution was apparent by the 1930s. InNew South Wales, many populations were lost to exten-sive vegetation clearance before any records were taken,especially in the west and along the east coast (Reed & Lunney 1990) (e.g., the lower Hunter River was loggedand cleared from 1801; (Knott et al. 1998). Lewis (1934)considered the koala exterminated in New South Wales, whereas Phillips (1990) estimated that there were “only hundreds” in that state in the late 1930s, “thousands in Victoria,” and “ten thousand left in Queensland.”In Victoria, the hunting industry had collapsed by 1910 due to a scarcity of koalas, and by 1934 koala num-bers in mainland Victoria were low—possibly   1000 an-imals (Lewis 1934, 1954; Lee & Martin 1988). Remnantpopulations possibly remained in the southwest, theMornington Peninsula, and South Gippsland (Lewis 1934),including Wilsons Promontory (Kershaw 1906, 1934).In South Australia, koalas were extinct by the 1930s(Robinson 1978; Phillips 1990).  Current   Our contemporary understanding of koala populationscomes from a series of surveys starting in the 1940s and anational survey undertaken in 1986. Distribution has beenassessed by community reports of sightings (Kikkawa &  Walter 1968; Campbell et al. 1979; Robinson et al. 1989;Phillips 1990; Reed et al. 1990; Menkhorst 1995; Lun-ney et al. 1996  a  , 1997; Patterson 1996), expert panels(Maxwell et al. 1996); intensive and systematic searches(Robinson 1978; Robinson et al. 1989; Menkhorst 1995),fecal pellet distribution (Phillips & Callaghan 1995; Munkset al. 1996; Sullivan 1998), combinations of community survey and fecal pellet surveys (Lunney et al. 1998, this is-sue), and call responses to taped calls and spotlighting(Jurskis & Potter 1997; Smith & Andrews 1997).   Conservation Biology  Volume 14, No. 3, June 2000    Melzer et al.Koala Distribution and Abundance   621   Various methods have been used to estimate koalapopulation numbers and density, including inferencefrom community surveys (Phillips 1990; Reed et al.1990), transect counts (Morgan 1997), mark-resight esti-mates (Caughley & Sinclair 1994; Hasegawa 1995), andquadrat searches (White & Kunst 1990; Melzer 1995).Survey methods suited the purpose of each investigationand the difficulties in estimating the numbers of thiscryptic animal.Data regarding koala populations have been stored onregional (Queensland) or centralized (New South Wales, Victoria, and South Australia) databases maintained by the wildlife authorities in each state. In Victoria andSouth Australia, records are sufficient to allow analysisof changing koala distribution.  NATIONAL  Koalas occur in Queensland, New South Wales, the Aus-tralian Capital Territory, Victoria, and South Australia.There are no wild koalas in Western Australia, Tasmania,or the Northern Territory. They are most frequently sighted in southeast Queensland and northeast New South Wales (Phillips 1990). The highest densities (8.6–8.9 koalas/ha) are found in habitat fragments in Victoria(e.g., Mitchell 1990) and South Australia (B. S. J., per-sonal observation), although low densities are also pres-ent (e.g., 0.7–1.6/ha, in Victoria [Hindell 1984];   1/hain South Australia [St. John, unpublished data]). InQueensland and New South Wales, population densitiesrange from low (e.g., 0.01/ha in central Queensland[Melzer & Lamb 1994]; 0.006/ha in Eden, New South  Wales [Jurskis & Potter 1997]) and moderate (e.g., 1–3/ ha in central and southeast Queensland [Gordon et al.1990  b  ; Hasegawa 1995]) to high (4–8/ha in parts of northeast New South Wales [Gall 1980; Faulks 1990]).Regional, state, and nationwide estimates of popula-tion size are few and inconsistent. The 1992 New South  Wales koala population was estimated to be between1,000 and 10,000 (Lunney et al. 1996  b  , 2000). The Aus-tralian Koala Foundation (Sharp 1995) put the nationalpopulation at 45,000–80,000 koalas (25,000–50,000 inQueensland and 10,000 – 15,000 in both New South  Wales and Victoria). This estimate contrasts sharply with estimates of 75,000–130,000 koalas for the StrathbogiePlateau Victoria alone (R. Martin, personal communica-tion). Disagreement regarding the size of the nationalpopulation has engendered a lack of confidence in fig-ures that do not have a scientific basis.  QUEENSLAND  State-wide surveys were undertaken in the 1960s and1970s by the Queensland Wildlife Preservation Society and in the 1980s as part of the National Koala Survey (Kikkawa & Walter 1968; Campbell et al. 1979; Patterson1996). The former relied on the returns from primary schools, the National Parks and Wildlife Service, and theForestry Department. Data for the National Koala Survey  were collected through field surveys conducted close tohuman settlements by volunteer labor, the collation of in-cidental reports, and community surveys. A comparison of the surveys by Kikkawa and Walter (1968), Campbell et al. (1979), and Patterson (1996)shows a range contraction in the north between 1967and 1985 and in eastern central Queensland from St.Lawrence to Gladstone (Phillips 1990; Maxwell et al.1996). Patterson (1996) attributed this loss to the broad-scale fragmentation of koala habitat across Queensland.Range reductions may have commenced before 1900 if anecdotal reports from Fraser Island are accepted (Phil-lips 1990).Fecal pellet surveys have been used to estimate thedistribution and relative density of koalas in the Prairie-Torrens Creek Alluvials Province of the Desert Uplandsbiogeographic region (Munks et al. 1996), Logan City insoutheast Queensland (Pahl 1996), and the Mulgalandsof southwest Queensland (Sullivan 1998). Near Mackay,M. Henry (personal communication) is using validatedcommunity records to assess the distribution of koalas inthe Pioneer Valley. These refine the distribution maps of Patterson (1996) and Phillips (1990) and extend our knowledge of the species’ western distribution.In Queensland koalas are widely distributed and occur at high density in some places. They are found in moistcoastal forests (Hasegawa 1995), in southern and central western subhumid woodlands (Gordon et al. 1990  a  ;Melzer 1995), and in some of the eucalypt woodlandsfringing watercourses in the semiarid west (Munks et al.1996; Sullivan 1998). Koalas also occur on islands off theQueensland coast. The populations on North Stradbrokeand Fraser (prior to 1900) Islands may have been natu-ral, whereas those on Brampton, St. Bees, Newry, Rab-bit, and Magnetic islands were introduced (Phillips 1990;Berck 1995).  NEW    SOUTH    WALES   As part of the National Koala Survey in 1986, New South  Wales and the Australian Capital Territory undertook com-munity-response surveys (Phillips 1990; Reed et al. 1990)supplemented by some limited field surveys (e.g., south-eastern forests) to determine distribution (Lunney et al.1996  a  , 1997). A comparison of these surveys with histori-cal data and surveys from 1949 and 1975 indicated that arange contraction and localized extinctions have oc-curred, particularly in southern and western parts of thestate (Phillips 1990; Reed & Lunney 1990; Reed et al.1990). The conclusion was that koalas have disappearedfrom about half their former range in New South Wales.Koalas are patchily distributed in the northeast, adja-cent parts of the Great Dividing Range, the eastern edgeof the western plains and associated drainage lines, and    622    Koala Distribution and AbundanceMelzer et al.  Conservation Biology  Volume 14, No. 3, June 2000  occasionally western New South Wales. They are now largely absent in the southern part of the state (Lunney & Leary 1988; Reed & Lunney 1990; Reed et al. 1990;Maxwell et al. 1996; Ellis et al. 1997; Lunney et al.1997).Direct census methods, such as spotlighting surveys(Jurskis & Potter 1997; Smith & Andrews 1997) and sys-tematic searches, and indirect methods, such as the inci-dence of fecal pellets (Phillips & Callaghan 1995) and re-sponses to taped calls, have provided detailed knowledgeof local koala distribution. These data have been used torefine local distribution maps (e.g., Iluka in northern New South Wales [Lunney et al. 1996  a  ] and Eden in southernNew South Wales [Lunney et al. 1997]). To provide infor-mation for land-use planning, independent field and com-munity surveys have been used to rank koala habitat froma geographical information system modeling procedurebased on a detailed vegetation map (Lunney et al. 1998,this issue).   AUSTRALIAN   CAPITAL    TERRITORY     AND    VICTORIA    A koala population of low density survives in the Austra-lian Capital Territory. It may have derived from koalasintroduced from Victoria, escapees from Tidbinbilla Na-ture Reserve (Phillips 1990; ANZECC 1998), or immigra-tion from New South Wales.The koala’s demise in Victoria was arrested by thetranslocation of several animals to Westernport Bay is-lands in the 1920s (Warneke 1978; Menkhorst 1995).These flourished, and the resulting overbrowsing of fod-der trees prompted translocations to other islands and tothe mainland (Menkhorst et al. 1998).Systematic fauna surveys, particularly spotlighting of Crown Lands, have generated thousands of koala sight-ings. This information has been supplemented with sightings from the 1960s and data from the 1985–1987National Koala Survey.Current koala distribution approximates the hypothe-sized range at the time of European settlement (Warneke1978; Martin 1989), but it is highly fragmented because of extensive clearing for pastoral and agricultural industriesand is strongly influenced by past intensive populationmanagement. The translocation program has been suc-cessful, and populations derived from released animalshave spread into the surrounding countryside. Koalas are widespread in coastal and lowland forests and woodlandsacross southern, central and northeastern areas, princi-pally south of the 500-mm isohyet and below 700 m ele- vation (Menkhorst 1995), with some in the drier Riverinaregion along riparian forest corridors (Warneke 1978).Dense populations have outstripped food resources,causing habitat damage, particularly in patches of coastmanna gum (    Eucalyptus   viminalis pryoriana   ). Translo-cations have been used to alleviate severe browse dam-age (Menkhorst et al. 1998).  SOUTH    AUSTRALIA   Coincident with the koala’s disappearance from South  Australia, animals were translocated from French Islandin Victoria to Kangaroo Island in the 1920s. Koalas fromQueensland, New South Wales, and Victoria were alsointroduced to the Mt. Lofty Ranges prior to the 1940sand subsequently were used to seed the Riverland koalapopulation (Lindsay 1950; Robinson 1978). Koalas fromKangaroo Island were introduced to southern Eyre Pen-insula in 1969 and reintroduced to their former range inthe lower southeast (Robinson 1978). Koala distributionhas been limited by the availability of suitable habitat,however, principally  Eucalyptus viminalis cygnetensis  and  E. v. viminalis  growing on fertile soils. In lower southeastern South Australia, clearing has reduced habi-tat. In the remaining areas, habitat was naturally limitedby climatic and edaphic factors (Robinson 1978; Phillips1990). Populations have expanded from the release sitesto occupy all suitable habitat, and dispersing animalshave been reported large distances from release sites(usually males, Robinson 1978), often in unsuitable habi-tats (e.g., Casuarina  spp. and mallee associations) where they probably fail to establish.The populations were sufficiently small and habitat suffi-ciently limited to permit intensive and systematic searchesduring the National Koala Survey. All were extant andbreeding. The Mt. Lofty Ranges population had declined fol-lowing wildlfires in 1983 (Robinson et al. 1989) and is now recovered substantially. These surveys revealed over-brows-ing in manna gum (    E. v. cygnetensis   ) habitat on KangarooIsland. In 1998 approximately 800 surgically sterilized ko-alas (vasectomy and tubal transection) were translocatedfrom Kangaroo Island to lower southeastern South Austra-lia. Sterile animals were used in the translocation to preventa recurrence of population growth and subsequent over-browsing at release sites.  Genotypic and Phenotypic Variation  Genotypic variation is recognized as important to biodi- versity conservation under state and federal legislationand under formal biodiversity strategies. Morphologicaland genetic variation (probably clinal) occurs in koalas(Thomas 1923; Troughton 1935; Melzer 1995; Sherwin etal., this issue) but is insufficient to support subspeciesclassifications (Sherwin et al., this issue). Genetic varia-tion in Victoria and South Australia koalas is low, reflect-ing the few individuals used to found the populationsused in those states’ translocation programs (Houlden etal. 1996). Regional variation is greatest in Queensland andNew South Wales but is poorly understood. The conserva-tion significance of losing regional variants during landclearing has not been studied but is discussed by Sherwinet al. in this issue.   Conservation Biology  Volume 14, No. 3, June 2000    Melzer et al.Koala Distribution and Abundance   623   Assessment of Distribution and Abundance  There are no nationally recognized standards for the as-sessment of koala numbers or distribution, and the tech-niques used suit the needs of individual projects. Thereare advantages and disadvantages associated with each method. For example, community-response survey re-sults may be influenced by the distribution of roads andpopulation centers (Ingram & Raven 1991). But whenthey are verified (e.g., through field survey and model-ing with vegetation maps) and when broad conclusionsare required [Lunney et al. 1997, 1998, this volume]),community-response surveys are effective and economi-cal. Intensive, systematic searches yield detailed informa-tion about the distribution and density of local popula-tions but have limited broadscale application. In South  Australia and Victoria, habitat is limited, so intensive sur- veying is a viable method. Mark-resight estimates (Caugh-ley & Sinclair 1994) have been used at replicated sites ina stratified sampling design to estimate koala numbers inthe Cygnet River valley on Kangaroo Island, South Austra-lia (B. St. J., personal observation). Broadscale applica-tion of the technique is precluded by time and logisticalconstraints. Census and density measures can be appliedmost usefully where an index of change over time issought, as in detecting a decline in koala densities fol-lowing large-scale fertility suppression in habitat isolatesin Victoria or South Australia. All regional and broadscale estimates of koala popula-tion size (e.g., Sharp 1995; R. W. Martin, personal com-munication) are derived by extrapolation from localizedhabitat densities. They rely on the assumption that thereare similar habitat types elsewhere that can be identifiedand mapped and that contain the same density of koalas.Therefore, estimates tend to vary widely.In Queensland, koala distribution, population size,and density are not well understood. Although Phillips(1990) and Patterson (1996) have described the extentof koala distribution, centralized and coordinated datacollection would facilitate a better understanding of dis-tribution, numbers, and changes over time. In New South Wales, the general extent of koala distribution is well understood. Variations in distribution and density occur within the koala’s range, however. Intensive sur- veys (e.g., Lunney et al. 1997; Phillips & Callaghan 1995;Smith & Andrews 1997) are beginning to provide morequantitative data. Koala distribution appears to be bestunderstood in Victoria and South Australia due to inten-sive management of koala populations and extensivemonitoring and recording of incidental koala sightings.  Limits to Current Distribution and Abundance  The most significant threat to koala distribution andabundance is habitat loss, although drought, wildfire,disease, predation, and collisions with vehicles are alsothreats. These threats vary in intensity throughout therange of the koala and between years, so specific con-clusions are difficult without further study.  Habitat Loss  Habitat destruction is the most significant threat to ko-alas (Reed & Lunney 1990; Maxwell et al. 1996; AN-ZECC 1998). There has been extensive clearing from thetime of European settlement to the present (Wells et al.1984; Sivertsen 1995), with  Eucalyptus  forest types suf-fering a 33–92% loss, depending on forest type (Graetzet al. 1995). Similarly, some  Acacia  landcover types (bri-galow and mulga) known to support low-density koalapopulations (Melzer & Lamb 1994; Munks et al. 1996;Sullivan 1998) have suffered an 80–86% loss (Graetz etal. 1995).Estimates of broadscale clearing of  Eucalyptus  land-cover types may overestimate habitat loss because they include eucalypt communities beyond the natural rangeof the koala. Furthermore, koalas utilize the scatteredtrees left after clearing, at least until dieback or other in-fluences claim the eucalypts within the vegetation rem-nant (Pahl et al. 1990). Nonetheless, estimates of clear-ing indicate direct loss of habitat and, by implication,koala populations (Pahl et al. 1990).Glanznig (1995) reported that as much vegetation wascleared nationally from 1945 to 1995 as in the previous150 years. In New South Wales, 25.7 million ha of forestor woodland, or 32% of the state, were ringbarked andpartially cleared between 1893 and 1921 (Reed 1991).Clearing is continuing, with most occurring in Queens-land and New South Wales. From 1983 to 1993 the esti-mated annual average clearing rate of native vegetation was 300,000 ha/year in Queensland and 150,000 ha/year in New South Wales (Glanznig 1995). Recent Queens-land estimates place the current clearing rate in Queens-land at approximately 262,000 ha/year (Queensland De-partment of Natural Resources 1997), most of which contains koala habitat. This ongoing habitat loss callsinto question the distribution results of the 1986 Na-tional Koala Survey. Koala distribution has declinedsince the completion of the survey.Clearing rates over the same period were approxi-mately 7780 ha/year in Victoria and 9300 ha/year inSouth Australia. Most clearing has occurred in nativegrasslands and mallee associations. Only 14% (1385 ha)of vegetation cleared in South Australia since 1983 couldbe considered koala habitat. The current rate of destruc-tion of native forest is low (Glanznig 1995), and less than1220 ha of native vegetation has been cleared in South  Australia since 1993. Thus, the loss of potential koalahabitat in Victoria and South Australia is small, and theemphasis is now on restoration and rehabilitation of rem-nants, including management of overbrowsing by koalas.
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