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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 Dynamics

Thursday 18th July, 10.15 - 12.15, Eliot Lecture Theatre 2

Chair: Ken Norris




(BLOCK CAPITALS indicate the presenting author)

10.15 - 10.30
CROSTI, ROBERTO, Philip G. Ladd and Kingsley W. Dixon., School of Environmental Science, Murdoch University, Murdoch, WA 6016, Australia, <roberto@central.murdoch.edu.au> (RC, PGL), Botanic Gardens and Park Authority, Kings Park and Botanic Garden-Science Directorate, West Perth, WA 6005, Australia (RC,KWD).

INFLUENCE OF POST-DISPERSAL SEED PREDATION ON GERMINATION IN A URBAN REMNANT BUSHLAND IN PERTH, WESTERN AUSTRALIA

A long-term study in the Kings Park urban remnant bushland showed there had been substantial changes in species abundance within the plant communities in the area over 60 years. A dramatic decline had occurred in the Banksia spp. which were once dominant in the woodland. Seed predation was hypothesised to be amongst the factors limiting the recruitment of Banksia spp. The objective of this study was to test this hypothesis by examining post-dispersal seed predation of the different key species of the bushland with particular emphasis placed on Banksia spp. Experimental exclusion of vertebrates and terrestrial invertebrates from seed caches revealed that Banksia seeds were exclusively predated by the former and rodents were likely to be responsible. The non-Banksia species which were included in the study have seeds of smaller size than banksias. Some of these were removed (no specific evidence that they had been eaten). Rate of loss, due to predation or removal, differed amongst the different species and were higher for the Banksia spp. On average covering seeds with litter, reduced seed loss by 45%. The Kings Park urban remnant had higher predation of Banksia seeds, compared with semi-prisitine areas outside the city and burned patches had lower rates than unburnt.

10.30 - 10.45
RODRIGUEZ-ORTEGA, CESAR E. and Miguel Franco. Instituto de Ecología, Universidad Nacional Autónoma de México, 10100 Coyoacán, D.F., México, <cerodrig@miranda.ecologia.unam.mx> (CERO), and Department of Biological Sciences, University of Plymouth, Drake Circus, Plymouth, PL4 8AA, UK (MF).

SEED LONGEVITY, DORMANCY AND GERMINATION IN THREE ENDANGERED, "SEROTINOUS" CACTUS SPECIES

Mammillaria hernandezii, M. napina and M. solisioides are three endangered cactus species in the Tehuacan-Cuicatlan Valley, Central Mexico. Like other members of this genus, their seeds are retained within the plant’s body (for up to 9, 12 and 9 years, respectively). We determined their seeds’ temporal dynamics (survival, viability and speed with which they germinate). Fruits are released at a species-specific, relatively constant rate and not in response to an environmental cue. Viability, measured as the proportion of germinating seeds, varied widely and was not correlated with seed’s age (e.g. 77% in 8-year old M. hernandezii seeds). Germination speed, however, increased with age. That is, given the opportunity (humidity) to germinate, older seeds do it faster. Slow release of fruits in these species introduces a time-lag mechanism that has important consequences on long-term population dynamics. It reduces both population growth and its temporal variability. This may account both for the rarity of these species and for their long-term population stability. This makes them highly vulnerable to habitat disturbance and has implications for the strategies required for their conservation.



10.45 - 11.00
GASCOIGNE, JOANNA C. and Romuald N. Lipcius. Virginia Institute of Marine Science, College of William and Mary, P.O. Box 1346, Gloucester Point, VA 23062, USA, <jo@vims.edu>.

LOW DENSITY REPRODUCTIVE FAILURE IN QUEEN CONCH: CAUSES AND CONSEQUENCES

Queen conch, Strombus gigas, are relatively mobile marine gastropods and are therefore not predicted to suffer from strong Allee effects. However observations show that populations below 50 conch per hectare suffer reproductive failure. We explored the mechanisms behind this observation using reciprocal transplants between high density (reproductive) and low density (non-reproductive) populations. Our results demonstrate that conch encounter rates alone do not explain the failure to reproduce, and we believe that conch require physiological or behavioural stimulation from conspecifics to induce reproductive activity. They may not therefore reproduce for several years after reaching sexual maturity. Conch seem to have evolved under conditions of high density, so this feature of their reproductive system may only recently have become maladaptive in the face of heavy and increasing exploitation throughout their range. A model of conch population dynamics shows that the Allee effect produces critical population density thresholds below which local extinction is likely, and that fishing mortality acts to increase these thresholds.



11.00 - 11.15
NORRIS, KEN, Peter Njoroge and Neil McCulloch. School of Animal & Microbial Sciences, University of Reading, Whiteknights, P.O. Box 228, Reading, RG6 6AJ, UK, <k.norris@reading.ac.uk> (KN & PJ), c/o RSPB, The Lodge, Sandy, Bedfordshire, SG19 2DL, UK (NM).

SAVING THE CRITICALLY ENDANGERED SEYCHELLES MAGPIE ROBIN — HOW CAN BEHAVIOURAL ECOLOGY HELP?

Designing effective management to restore populations of critically endangered species is hampered by a lack of data. This problem is particularly acute when individuals are released into vacant habitat to develop new populations. Even if detailed demographic data are available it is unlikely that the population will have experienced the exact range of population densities and environmental conditions in the past that it will experience in the future. This makes the use of classical demographic models unreliable. Instead, here we show how theories developed by behavioural ecologists can be used to provide insights into density-dependent/regulatory processes operating in populations of the critically endangered Seychelles magpie robin. We examine mechanisms of competition for breeding resources that affect fecundity and survival, and illustrate the implications of these mechanisms for regulatory processes operating in good and poor quality habitats. We go on to show how this understanding can guide management decisions; in particular how the growth of populations established on new islands by translocation can be maximised.



11.15 - 11.30
DIETZ, JAMES, Jonathan Ballou and Andrew J. Baker. Department of Biology, University of Maryland, College Park, MD 20742, USA, <jd72@umail.umd.edu> (JD), Conservation and Research Center, Smithsonian National Zoological Park, Washington DC 20008, USA (JB) and Zoological Society of Philadelphia, 3400 W. Girard Ave., Philadelphia PA 19104, USA (AJB).

EFFECTS OF INTENSE PREDATION ON THE DEMOGRAPHY AND GENETIC EFFECTIVE SIZE OF ISOLATED POPULATIONS

Here we report estimates of demographic parameters and effective population size (Ne) before and after intense predation in a forest "island" reserve. Since 1986 we continuously monitored demographic variables in a study population of golden lion tamarins in the 6300 ha Poço das Antas Reserve, Brazil. Prior to 1996, predation on tamarins was rare and typically resulted in death of one or two individuals per event. All suitable habitat was occupied by stable breeding groups with significant between-group differences in long-term reproductive success. However, from 1996 through 2000 predation on tamarins increased significantly, typically resulting in loss of complete breeding groups. The number of tamarins in the reserve dropped from ca. 350 to ca. 220. Recolonisation of vacant habitat was rapid, but new groups often contained breeding adults without reproductive experience and lacked helpers. Infant survival to weaning dropped from 70% to 11%. In conclusion, increased predation rates substantially altered demographic characteristics of this small population. While reduced population size, survival and generation time are expected to reduce Ne, turnover in breeding individuals could mitigate these effects. The long-term impacts of this 5-year predation bout on Ne will depend on the population’s capacity to recover in size and group stability.



11.30 - 11.45
COURCHAMP, FRANCK, Greg Rasmussen and Claire Thomas. Ecologie, Systématique & Evolution — CNRS - Université Paris XI - Bât 362 - F-91405 Orsay Cedex — France, <franck.courchamp@ese.u-psud.fr> (CF), WildCRU, Department of Zoology, University of Oxford, UK (GR), Whitstead, Newnham College, University of Cambridge, Cambridge, UK (CT).

IMPLICATIONS OF THE NATURALLY BIASED SEX RATIO OF LYCAON PICTUS FOR ITS CONSERVATION

The painted hunting dog or African wild dog, Lycaon pictus, is one of the most endangered large carnivores in Africa, with extinction predicted within a few decades if their dramatic decline is not stopped. Lycaon is an obligate cooperative breeder living in packs of up to 20 adults, in which most of the time only the alpha pair breeds; the remaining adults are reproductively suppressed and help to raise the pups. The resulting female oestrogen levels lead to a naturally biased sex ratio in the litters: primiparous litters are male biased (c. 2/3 males) and multiparous litters are female biased (c. 2/3 females). In this work, we investigate the effects of the current high level of anthropogenic mortality on painted hunting dogs: as females survive to produce fewer litters than previously, this is likely to result in a greater proportion of litters being primiparous and consequently male biased. With a mathematical model of the dynamics of a population of nine Lycaon packs, we show that lowering the survival of dominant females has an important impact on the population, not only by much diminishing its final size, but also but by disrupting the entire social structure of the population.



11.45 - 12.00
MARKER, LAURIE, and Amy Dickman. Cheetah Conservation Fund, P.O. Box 1755, Otjiwarongo, Namibia and Wildlife Conservation Research Unit, Department of Zoology, South Parks Road, Oxford OX1 3PS, UK, <cheeta@iafrica.com.na> (LM and AD).

CHEETAH REMOVAL ON NAMIBIAN FARMLANDS: REASONS, RATES AND CONSERVATION IMPLICATIONS

Cheetahs, Acinonyx jubatus, have undergone serious decline worldwide, and the largest free-ranging population is now found in Namibia. Ninety percent of Namibia’s cheetahs are found outside of protected areas on commercial farms, where they come into conflict with local farmers and are often removed in large numbers. A ten-year study was conducted on the Namibian farmlands to investigate the reasons for removal, demography of the removed cheetahs, and possible solutions for alleviating the conflict. Conflict with farmers caused 91.2% of live cheetah captures and 47.6% of wild cheetah deaths reported. The majority of cheetah captures (52.7%) occurred due to a perceived threat to livestock, but in only 3% of cases was there any evidence that the cheetahs caught were indeed causing a problem. Cheetahs were often captured opportunistically rather than in direct response to stock loss. The majority of the cheetahs removed were of prime breeding age, which is likely to be particularly detrimental to the population. The level of removals dropped significantly through the study, however, from 19 cheetahs removed annually per farmer to 2.1 by the end of the study. This indicates that local attitudes and actions can be positively influenced through long-term education and conservation awareness programmes.



12.00 - 12.15
LOUCKS, COLBY, Eric Wikramanayake, and Eric Dinerstein. World Wildlife Fund - United States 1250 24th St. NW, Washington DC 20037, USA, <colby.loucks@wwfus.org>.

Humans, habitat, and biodiversity: Relations between human populations and habitat loss in the Indo-Pacific

The increasing use of natural resources by a burgeoning human population is commonly associated with loss of biodiversity. Here, we used two population parameters–human population density and distribution pattern in relation to distance of remaining forest blocks–to measure chronic anthropogenic degradation threats to biodiversity in the Indo-Pacific region. Using ecoregions, we found a high correlation between human population density and the percent of habitat loss, and thus biodiversity loss. We analysed the data in relation to bioregion, biome, elevation (i.e., lowland and montane ecoregions), and species richness and endemism. As a general trend, ecoregions of the Indian Subcontinent and Sunda Shelf and Philippines bioregions have higher human population densities and have lost a greater percentage of forest cover. Across all bioregions, the lowland tropical moist forest, tropical dry forest, and mangrove ecoregions were the most densely populated and have suffered greatest habitat loss. In general, lower elevations contained higher population densities and less remaining habitat, but in several regions population pressures were severe in montane ecoregions. This analysis shows that human population density and distribution can be used as an indicator of threat to forest cover and biodiversity.