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Society for Conservation Biology: 2002 Annual Meeting

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Society for Conservation Biology: 2002 Annual Meeting

Society for Conservation Biology 16th Annual Meeting July 14-July 19 2002
co-hosted by DICE and the British Ecological Society


Abstracts for Population Monitoring
Session One

Monday 15th July, 15.30 - 17.30, Grimond Lecture Theatre 3

Chair: Larissa Bailey




(BLOCK CAPITALS indicate the presenting author)


15.30 - 15.45
WILLIAMS, ALISON, and James Berkson. Department of Fisheries and Wildlife Sciences, Virginia Polytechnic Institute and State University, Blacksburg, VA, USA, <alwilli2@vt.edu>

REDUCING FALSE ABSENCES IN SURVEY DATA: ESTIMATING DETECTION PROBABILITIES OF Plethodon cinereus

Surveys to determine the presence or absence of a species may be used for monitoring programs, inferences about the species’ probability of occurrence, or management decisions. Errors in presence/absence data can result from false absences, where the species is actually present at the site, but not detected. We designed an experiment to estimate the probability of detection of redbacked salamanders (Plethodon cinereus) using different sampling methods and salamander densities. Salamanders were introduced into enclosures (n=124), which were randomly assigned to a sampling treatment, either daytime cover object searches or nighttime visual searches, and a density treatment, either low or high densities of P. cinereus. Probability of detection was significantly higher using daytime cover object searches and in enclosures with high salamander density. Weather conditions influenced the probability of detection. Increases in temperature correlated with decreases in detection during daytime cover object sampling. Humidity was a limiting factor to detection during nighttime visual sampling and rainfall was positively related to detection during nighttime surveys and daytime surveys in high density enclosures. Probability of detection estimates are important for survey design and analysis of presence/absence data. A simulated application of these results to a monitoring program will be presented.

15.45 - 16.00
BAILEY, LARISSA L., Theodore R. Simons, and Kenneth H. Pollock. Cooperative Fish and Wildlife Research Unit, Department of Zoology, North Carolina State University, Raleigh, NC 27695, USA, <llbailey@unity.ncsu.edu> (LLB, TRS), Department of Statistics, North Carolina State University, Raleigh, NC 27695, USA (KHP).

ESTIMATING TEMPORARY EMIGRATION AND DETECTABILITY IN PLETHODON SALAMANDERS USING POLLOCK’S ROBUST DESIGN

Recent concern over global amphibian populations has highlighted a need for more extensive, rigorous monitoring programs to detect and determine the causes of declines. Most monitoring programmes face two important sources of variation: spatial variation and detectability. We used Pollock’s robust design in a three year capture-recapture study to estimate detectability and temporary emigration for plethodon salamanders in Great Smoky Mountains National Park. We used 12 competing models to determine the importance of temporary emigration and explored temporal and behavioural variations in capture probabilities. Models that included random temporary emigration were chosen slightly more often than models with no emigration. The ‘best’ model, which contained random emigration, was selected two times more often than any other model. Models incorporating Markovian emigration were difficult to fit, mainly due to lack of convergence for the immigration parameter. Models that contained behavioural effects in capture probabilities were selected more often than models without behavioural effects. Our study is the first to formally estimate temporary emigration in terrestrial salamander populations, and our results indicate that significant portions of terrestrial salamanders are subterranean. Therefore, we caution against using unadjusted count indices to compare populations over time or space without attempting to estimate detectability.



16.00 - 16.15
SIMONS, THEODORE R., Erin J. Hyde, Larissa L. Bailey, and Kenneth H. Pollock. Cooperative Fish and Wildlife Research Unit, Department of Zoology, North Carolina State University, Raleigh, NC 27695, USA, <tsimons@ncsu.edu> (TRS, EJH, LLB), Department of Statistics, North Carolina State University, Raleigh, NC 27695, USA (KHP).

SAMPLING PLETHODONTID SALAMANDERS: SOURCES OF VARIABILITY
Recent evidence of possible worldwide amphibian population declines has highlighted the need for a better understanding of species-specific habitat associations and methodologies for monitoring long-term population trends. We present data on spatial and temporal patterns in salamander diversity and abundance in Great Smoky Mountains National Park and compare the bias and effectiveness of four common sampling techniques. We found that large-scale habitat characteristics including disturbance history, proximity of streams, and elevation are useful in explaining patterns of salamander distribution and abundance. Microhabitat variables did not explain much of the variation in salamander relative abundance. Data collected over two years suggest that common salamander sampling techniques vary significantly in their effectiveness, and they may often violate assumptions required for comparing salamander population indices over space or time. Salamander counts on our sites were highly variable. Neither sampling variability nor detectability were constant across habitat types or species. These characteristics reduce power for detecting long-term population trends, and suggest that some common sampling methods may not provide indices suitable for long-term population monitoring.



16.15 - 16.30
WARD BOOTH, JANE, and Georges Dussart. Ecology Research Group, Canterbury Christ Church, University College, Canterbury, Kent CT1 1 QU, UK, <JFWardBooth@compuserve.com> (JF).

AUTOECOLOGICAL STUDY OF EFFECT OF LAND-USE ON THE ECOLOGY OF THE
TERRESTRIAL SNAIL MONARCHA CANTIANA.

Monarcha cantiana is a major component the terrestrial malacofauna of southern but not northern Britain. The objective of the study was to investigate how agricultural land-use affected the demography of this species. In surveys of farmland in south east England between 1997-2000, abundance and population structure of M. cantiana varied between years but also varied in relation to abundance and diversity of vegetation. A survey across several seasons indicated slow growth of juveniles, a type III pattern of survivorship (Pearl, 1928) and after significant over-wintering mortality, re-colonisation of the sites in the following year, from foci such as ditches. There was also some evidence of predation by small mammals. These results are significant for both farm management and molluscan conservation.



16.30 - 16.45
LANDENBERGER, RICK, James McGraw, Timothy Warner, and Tomas Brandtberg. Department of Biology, West Virginia University, P.O. Box 6057, Morgantown, WV 26506-605, USA, <rlanden@wvu.edu> (RL, JM), Department of Geology and Geography, West Virginia University, P.O. Box 6300, Morgantown, WV 26506-6300, USA (TW, TB).

POTENTIAL OF COLOR-INFRARED DIGITAL IMAGERY FOR AERIAL CENSUS OF HALEAKALA SILVERSWORDS

High spatial resolution remote sensing offers largely untapped potential for censusing and monitoring rare plant populations. The Haleakala silversword is a federally listed threatened species whose natural range is restricted to the highest elevations on Maui. With its distinctive foliage set against the volcanic background, the species provides an excellent test of the capabilities of colour-infrared remote sensing to provide a spatially explicit, individual-based approach to monitoring. We used a helicopter-mounted, high spatial resolution digital camera system with a colour-infrared filter to image a series of permanent census plots. Ground-based censuses from 2001 were compared to photointerpretation and automated computer classification of super-high resolution colour-infrared imagery. Errors of omission and commission occurred in both methods, although at low rates. Photointerpreters and automated classification accurately estimated silversword size in aerial images, with higher accuracy in the larger size classes. Although imperfect, both photointerpretation and classification effectively differentiated between living and dead individuals. Relative to photointerpreters, flowering individuals presented challenges for the classification. Although not as accurate as localised ground-based censuses, high resolution aerial censuses provide a rapid partial population census over larger areas, which may be adequate for monitoring rare plants growing in barren landscapes.




16.45 - 17.00
NGHIKEMBUA, MATTI T., Ngaturue D. Muroua, Richard M. Jeo, Fanuel E. Ekondo and Laurie L. Marker. Cheetah Conservation Fund, P.O. Box 1755, Otjiwarongo, Namibia, <cheeta@iafrica.com.na> (MTN, NDM, RMJ, FEE, LLM).

ASSESSING THE ECOLOGICAL IMPACT OF BUSH ENCROACHMENT ON NAMIBIAN FARMLANDS

During the past century, Namibia’s farmlands have become steadily more encroached with thick bush, mainly of Acacia mellifera, Acacia reficience and Dichrostachys cinerea species. The full impact of such habitat change is uncertain, but the encroachment has resulted in lowered productivity on the farmlands, altered the local ecology and has potentially damaging consequences for Namibia’s cheetah (Acinonyx jubatus) population, which is the world’s largest remaining free-ranging population and is found mainly on the commercial farmlands. We report on the results of a long-term study that has assessed the distribution and ecology of ungulate species on the farmlands and revealed that they show habitat preference for more open areas, with only 1.4% of ungulate recordings being made in thick bush. Habitat preference differs between species and seasons, but the results indicate that bush encroachment may have important consequences for several ungulate species, and therefore also for rare carnivores such as cheetahs on the Namibian farmlands which utilise these species as a prey base. These results provide vital baseline information on species abundance and distribution on the farmlands, and will provide comparative data for a new project examining the ecological impact of bush removal in Namibia.



17.00 - 17.15
SANDERSON, FIONA J and Paul W Bright. School of Biological Sciences, Royal Holloway, University of London, Egham, Surrey TW20 0EX, UK, <F.Sanderson@rhul.ac.uk> (FJS, PWB).

CHANGES IN DORMOUSE POPULATIONS IN THE LAST DECADE: REGIONAL PATTERNS AND CAUSES

The hazel dormouse, Muscardinus avellanarius, has disappeared from about half of its range in Britain in the last 120 years, probably due to loss and fragmentation of its ancient woodland habitat and to the cessation of traditional woodland managment. The National Dormouse Monitoring Programme was set up in the late 1980s in order to monitor remaining populations and detect any further declines and population extinctions. Using log-linear Poisson regression models and generalised additive models to model population changes since the early 1990s both over the dormouse range in Britain as a whole and in different regions of the country, we have detected a substantial population decrease (approximately 40-60%) in the north and west of the country since 1993, and the probable extinction of at least one population over this period. This region is at the edge of the range of the dormouse both in Britain and Europe, and further analysis suggests that population changes in this region may be linked to climate. Our work suggests that populations in these regions are vulnerable and this may lead to further range contraction, but that different processes are affecting populations in core areas in the south of the country, which are more stable.



17.15 - 17.30
STEVENSON, ROBERT D., David C. Mountain, and Timothy A. Purinton. Department of Biology, University of Massachusetts Boston, Boston, MA 02125-3393, USA, <robert.stevenson@umb.edu> (RDS), Dept. of Biomedical Engineering, Boston University, 44 Cummington Street, Boston, MA 02215, USA (DCM), Massachusetts Audubon Society, North Shore Office, 346 Grapevine Road, Wenham, MA 01984, USA (TAP).

MONITORING ANADROMOUS HERRING POPULATIONS IN MASSACHUSETTS: IMPACTS AND CHALLENGES OF CITIZEN SCIENCE

Anadromous river herring (the alewife, Alosa pseudoharengus, and the blueback, Alosa aestivalis) are still harvested by humans in river systems of eastern North American, but the construction of dams and over-harvesting have reduced and extirpated populations. Despite their importance in freshwater ecosystems and current value as fish bait, few data exist on population changes. Beginning in 1997 the Parker River Clean Water Association (http://www.parker-river.org/) organised a group of conservation organizations and volunteers to monitored the upstream migration knowing that monitoring efforts by scientists in the 1970’s provided historical data. Citizens counted alewives moving through fishways during April and May for 10 minutes of an hour period. Linear extrapolation was used to estimate populations for each hour and during sampling intervals without counts. For the last five years, 1997 to 2001, the estimated run size averaged 5700 fish (range 2200-8000) whereas for seven years in the 70’s the average was 20,400 (range 6600-38000) indicating a reduction in population size by about three-quarters. The monitoring effort has been instrumental in getting adults and children to the river, garnering funds for restoration of fishways, in modifying constructions projects that impact the river, and for initiating monitoring efforts in other nearby watersheds.