bluuebunny/crossref_metadata_2025_split huggingface dataset:
Differential body condition and vulnerability to predation in snowshoe hares
Authors: Murray Dennis L. 
Published: March 2003

Summary

Selection of prey in poor body condition allegedly is a widespread phenomenon in predator–prey systems. Yet, it remains unclear to what extent such selection reflects impeded prey escape ability due to severe malnutrition and/or state‐dependent risk taking following lesser changes in prey body condition. In systems where prey food availability is adequate, few individuals should be severely malnourished and thus condition‐sensitive predation should be related principally to changes in nutritional status that occur irrespective of an individual's absolute body condition.
I studied predation in snowshoe hares ( Lepus americanus
, Erxleben) when food was abundant, to test the prediction that change in body condition would contribute, more than would absolute body condition, to vulnerability to predation. Hares (
n

=
618) were radio‐marked and monitored for survival while body condition was indexed during bimonthly livecaptures. A subsample of animals (
n = 36) was equipped with motion‐sensitive transmitters and activity patterns were examined in relation to the body condition index and vulnerability to predation.
Manipulation of hare nutritional status via food supplementation improved hare body condition but did not affect vulnerability to predation; reduction of nematode parasite numbers did not improve hare condition but reduced predation among female hares. Reproductive status affected predation in both sexes, with recently pregnant females and non‐scrotal males being less vulnerable to predation. Heavier males also tended to experience lower predation rates.
Predation rates for both female and male hares were higher among individuals having recently experienced condition deterioration but not among animals considered to be in poor absolute condition. Yet, the parameter representing change in condition was the last to enter survival models, indicating a relatively modest effect of this factor on hare vulnerability to predation. Mammalian but not avian predators tended to kill hares in declining condition, and hare activity patterns were not correlated either to change in condition or to survival.
These findings indicate that nutritional status may influence vulnerability to predation even when food is abundant, but that such effects occur indirectly through changing body condition. This implies that hares are likely to forage in a risk‐prone manner when subject to worsening condition.
Small and large anemonefishes can coexist using the same patchy resources on a coral reef, before habitat destruction
Authors: Hattori Akihisa 
Published: March 2003

Summary

According to meta‐population models, a superior competitor and a superior disperser can coexist in a patchy environment. The two anemonefishes, a large aggressive Amphiprion clarkii
Bennett and a small less‐aggressive
A. perideraion
Bleeker, use the same host anemone
Heteractis crispa Ehrenberg on a coral reef, Okinawa, Japan, where most of the hosts disappeared after the coral bleaching in 1998. Their microhabitat (host) use and coexistence, and the quality and quantity of microhabitats were investigated in 1988, 1989, 1999 and 2000 on the coral reef. Their interspecific interaction was also examined.
Before the habitat destruction, the two species coexisted. Although A. clarkii
was behaviourally dominant over
A. perideraion
in a cohabiting group,
A. perideraion
was a superior competitor in terms of site displacement, because
A. perideraion
could displace a microhabitat. Adult
A. clarkii
emigrated from a cohabiting group probably due to the high cost of interactions with adult
A. perideraion
. Although it is easier to defend a small area for a larger species, sharing a host with adult
A. perideraion
may not pay for
A. clarkii
because
A. clarkii needs a larger area.
A. clarkii
was not only a superior disperser, which was able to find a vacated host, but also a pioneer species that was able to use newly settled small hosts. Larval
A. clarkii
settled on such a small host because they were able to move to larger hosts for future reproduction, while
A. perideraion did not settle on a small host because of low mobility after settlement. Microhabitat (host) with various sizes might have promoted their coexistence.
After the habitat destruction, the superior competitor A. perideraion went extinct locally due probably to lack of small host utilization ability. The present study implies that the difference in body size between the two competitors plays an important role in their coexistence, because species with different body sizes can have different mobility and require different amounts of resources.
Niche‐oriented species–abundance models: different approaches of their application to larval chironomid (Diptera) assemblages in a large river
Authors: Fesl Christian 
Published: March 2003

Summary

Species–abundance patterns of larval chironomid assemblages in a large river were tested against seven niche‐oriented models, using data on abundances measured monthly at four sites along a cross‐section of the River Danube in Austria.
Expected abundance patterns generated by computer simulations were tested against two categories of assemblages: all species found and the dominant species only. Within each category, the whole river cross‐section was compared with the four single sites, and three functional feeding groups were analysed separately. For all assemblages, species‐ and process‐oriented approaches concerning the correspondence between species identity and abundance ranking were used.
When all 81 species found within the river section were included, none of the models agreed with the observed process‐oriented patterns, whereas the distributions of collector–gatherers, filterers and (at a single site) grazers fitted the Random Fraction model. This model indicates that the species divide the niche space in a random fashion, with no hierarchy of dominance. None of the models fitted the species‐rich assemblages using the species‐oriented approach.
When only the most abundant species were considered, several of the models fitted the observed assemblages. The Random Assortment model provided best‐fits most frequently, suggesting that relative abundances of the species are completely independent. However, the Random Fraction model agreed with observed patterns of abundance in about 50% of cases when the Random Assortment model provided a good fit.
Only 25% of all species‐oriented patterns of the most dominant species were described by the seven models, mostly by the Random Assortment model. However, species classed as filterers showed a tendency towards more even distributions according to the MacArthur Fraction model and the Dominance Decay model.
Results suggest that the Random Fraction model corresponds best with species‐rich assemblages whereas this model combined with the Random Assortment model may provide a good explanation for patterns formed by the (relatively few) most dominant species. The species‐oriented approach might be a valuable additional form of analysis for uncovering tendencies in abundance patterns which could be overlooked when focusing solely on the process‐oriented approach that is usually used.
Spoor counts as indices of large carnivore populations: the relationship between spoor frequency, sampling effort and true density
Authors: Stander P. E. 
Published: March 2003

1. Studies of large carnivore populations and, particularly, reliable estimates of population density are necessary for effective conservation management. However, these animals are difficult to study, and direct methods of assessing population size and density are often expensive and time‐consuming. 2. Indirect sampling, by counting spoor, could provide repeatable and inexpensive measures of some population parameters. The relationship between true population density and indirect sampling results has seldom been described in large carnivore studies. 3. In northern Namibia the population densities of leopards, lions and wild dogs were measured through recognition of individuals and groups. Spoor counts were then conducted independently, to assess the relationship between true density and the distribution of spoor. 4. Sampling effort, both in terms of the number of roads and total road distance in a sample zone, and the intensity of sampling, had a marked effect on the accuracy and precision of spoor frequency calculations. 5. In a homogeneous habitat, leopard spoor were evenly spread along different roads and spoor frequency was independent of road length. Taking into account very low sample sizes, the spoor density of leopards, lions and wild dogs showed a strong linear correlation with true density. The slope of the regression for leopards was different to that of lions and wild dogs.
Foxes, rabbits, alternative prey and rabbit calicivirus disease: consequences of a new biological control agent for an outbreaking species in Australia
Authors: Pech R. P. , Hood G. M. 
Published: March 2003

1. Rabbit calicivirus disease (RCD; also known as rabbit haemorrhagic disease) has been introduced recently as a biocontrol agent for rabbits in Australia. The consequences for fox populations that use rabbits as primary prey, for populations of alternative native prey, and for pastures, were examined using a model for rabbit‐ and fox‐prone areas of semi‐arid southern Australia. 2. Existing data were used to quantify the interactions of foxes, rabbits and pasture. A generic model for predation on native herbivores was constructed by modifying the density‐dependent (Type III) functional response of foxes to rabbits to a depensatory (Type II) response that is appropriate for alternative prey. Similar dependence on pasture biomass was assumed for the dynamics of both rabbits and alternative prey in order to identify clearly the consequences of differing predation. In the absence of quantitative data for Australian conditions, the epidemiology of RCD was simulated empirically to mimic a range of potential patterns of occurrence. 3. For semi‐arid Australia the model predicts that as the frequency and intensity of RCD epizootics increases: (i) the mean abundance of rabbits will decline, as will the frequency of eruptions of rabbits; (ii) there may be little increase in mean pasture biomass and a small decrease in periods of very low pasture biomass when competition between herbivores is most intense; (iii) the mean abundance of foxes will decline; (iv) there will be a reduced frequency of occasions when rabbit density is low but fox density is high due to a lag in the response of predator populations; and (v) there is potential for an increase in the mean abundance of alternative prey and in the proportion of time their density exceeds a threshold comparable to that currently required for eruptions of rabbits.
Breeding bird communities in pine plantations of the Spanish plateaux: biogeography, landscape and vegetation effects
Authors: DÍAZ M. , CARBONELL R. , SANTOS T. , TELLERÍA J. L. 
Published: March 2003

Summary

Afforestation with pines (Pinus pinaster and, to a lesser extent, P. pinea and P. halepensis) seems to be the most probable land‐use change over large areas of dry cereal croplands in central Spain in the next 10–20 years. This will be encouraged by changes in the subsidy policies of the Common Agricultural Policy that aim to decrease food production and restore the environmental diversity previously lost through agricultural intensification. This study addresses the factors influencing the richness and composition of breeding bird communities in these pine plantations and evaluates the potential environmental benefits of the afforestation programmes.
The complement of bird species breeding in 88 plantations ranging in size from 0.1 to 6775 ha was determined. Plantations were characterized according to size, distance to the nearest large plantation, vegetation structure and geographical location (northern moist vs. southern xeric Iberian plateaux).
Plantation size alone accounted for 67–75% of the variation in species richness, and was also the maintrait explaining the patterns of presence/absence of most individual bird species. Plantations smaller than 25 ha only maintained 50% of the regional pool of forest birds during breeding, whereas this proportion increased to 69–86% for plantations of 25–100 ha. Geographic location, degree of isolation and vegetation structure were also important. Bird species richness decreased with distance to a large plantation, and increased with prevalence of undergrowth shrubs and with plant species richness.
Both species richness and the incidence of individual species in plantations were affected by geographical location. They were greater in plantations of the northern plateau, reflecting a trend of increasing densities of most forest bird species in Spain in more northerly locations.
The results of this study suggest that re‐afforestation of former arable land in the Spanish plateaux is unlikely to increase species richness in forest bird communities. Given the regional scarcity of many forest birds and the small scale of new plantations, re‐afforestation schemes are unlikely to promote rich forest bird communities.
Since plantations are unsuitable habitats for the bird species breeding in Spanish dry cereal croplands, and such birds have a high conservation value because of their small and declining populations the overall environmental benefits of large‐scale afforestation programmes will not include increased diversity of birds.
Does carbaryl increase fluctuating asymmetry in damselflies under field conditions? A mesocosm experiment with Xanthocnemis zealandica (Odonata: Zygoptera)
Authors: Hardersen Sönke , Wratten Steve D. , Frampton Chris M. 
Published: March 2003

Summary 1. Previous laboratory experiments have shown that the insecticide carbaryl reduces emergence success and increases fluctuating asymmetry in cell patterns of damselfly wings. These effects were validated using mesocosms. Twenty artificial ponds, each containing Xanthocnemis zealandica, were exposed to three replicated (n = 5) concentrations of carbaryl contamination plus controls. Emergence success, level of fluctuating asymmetry in meristic and metric traits of the wings, and average size of the damselflies were measured. 2. The degradation of carbaryl was relatively constant for the first 5 weeks but later increased considerably, probably because of enhanced biodegradation. 3. Carbaryl at 100 p.p.b. (nominal concentration) reduced emergence success 10 days after application, whereas carbaryl at 10 p.p.b. and 1 p.p.b. had no effect. 4. To investigate how the level of fluctuating asymmetry and size were affected by carbaryl, damselflies from ponds with the highest concentration where emergence success was not affected (10 p.p.b.) were analysed over four time periods. Fluctuating asymmetry of the wings increased during the season but was not affected by carbaryl at 10 p.p.b. 5. Size, measured as average length of the front wings, was affected by date of emergence but not by exposure to carbaryl at 10 p.p.b. 6. Three main reasons for the absence of increased levels of fluctuating asymmetry as a result of carbaryl exposure are suggested.
A comparison of Eurasian red squirrel distribution in different fragmented landscapes
Authors: Rodríguez Alejandro , Andrén Henrik 
Published: March 2003

Summary 1. The occurrence of species vulnerable to habitat fragmentation is likely to depend on the size and separation of the fragments. However, the shape of the function that relates occurrence to these landscape parameters may be affected by other factors that are less easily measured, in which case relationships with size and separation in one area may predict occurrence elsewhere only poorly. 2. We explored how well the distribution of red squirrels Sciurus vulgaris in fragmented woodlands was predicted by simple logistic regression models empirically derived in other fragmented landscapes. 3. Comparisons between predictions lead us to identify thresholds in fragment size (> 10 ha) and distance to a source (< 600 m) where the probability of squirrel occupancy was at least 0·9 in all landscapes. These values may reflect squirrel minimum habitat requirements for home range and dispersal in the worst study area. 4. For fragments < 10 ha (outside shared thresholds), models developed in a landscape could predict squirrel occupancy elsewhere only in 17% of cases, as other factors such as demography or habitat quality might become relevant in very small and isolated fragments. 5. The predictive ability for small fragments also improved when the range of fragment sizes in the area of observation fell within the range of sizes in the area where the model was developed. 6. Some models gave correct between‐year predictions of squirrel distribution in the same landscape despite noticeable changes in regional squirrel population density. 7. When size and distance thresholds were met, we found that models could be used successfully elsewhere. In addition, threshold values indicate how large forest fragments should be and how they should be arranged to favour squirrel occurrence in a landscape.
Juvenile guanaco survival: management and conservation implications
Authors: Sarno Ronald J. , Clark William R. , Bank Michael S. , Prexl Walter S. , Behl Michael J. , Johnson Warren E. , Franklin William L. 
Published: March 2003

Summary1. The Chilean National Forestry and Park Service is striving to implement a guanaco management programme of sustained‐yield use. To achieve this, the rate, variation and causes of juvenile guanaco mortality must be understood thoroughly. Therefore, we monitored the survival of 409 radio‐collared juvenile guanacos in Torres del Paine National Park, Chile, from 1991 to 1996.2. The Kaplan–Meier product limit estimator of survival for staggered entry was calculated, and survival rates between juvenile males and females and among years were compared using thelifetestprocedure in SAS. The Cox proportional hazards model was used to relate mortality rate to explanatory variables such as juvenile sex, birth weight, adult female aggression towards researchers during the capture and tagging of newborns, population density, and mean monthly winter snowfall.3. Mean juvenile survival rate (Ŝ) was 0·38, but varied between 0·31 and 0·55. Survival rates between the sexes were not significantly different, although male survival was lower than that of females. Mortality rate was highest during the first 14 days after birth. Most deaths occurred between birth and 7 months of age.4. The risk of mortality increased by almost 6% with every 1 cm increase in winter snowfall, whereas the risk of mortality decreased by almost 24% as adult female aggression increased towards researchers.5. Current management objectives are aimed at the implementation of a rational harvest of guanacos on the Chilean side of the island of Tierra del Fuego. Our results provide improved and updated estimates of juvenile guanaco survival and will aid in the modelling of harvest rates of guanacos in southern Chile. Future proposed harvests from wild populations in southern Chile need to consider the rate and variation of this critical life‐history parameter.
Hunting effort and game vulnerability studies on a small scale: a new technique combining radio‐telemetry, GPS and GIS
Authors: Brøseth Henrik , Pedersen Hans ChR. 
Published: March 2003

Summary1. Global positioning systems (GPS) were used to track hunters in an area of central Norway where willow ptarmiganLagopus lagopuswere contemporaneously radio‐tracked. A geographical information system (GIS) was then used to study spatiotemporal interactions between hunters and game.2. Recording hunting activity with the GPS produced accurate and unbiased information about the behaviour and effort of hunters. When GPS tracking nine hunters during 50 hunter‐days, data were lost for an estimated time of 30 h 45 min, which constituted about 10% of the total hunting time.3. Willow ptarmigan hunters walked on average 16·2 km daily at a speed of 2·8 km h–1, and they hunted for 9 h each day, of which almost 6 h was active hunting time. During 50 hunter‐days they had 295 h of active hunting, covered a distance of 818 km and harvested 20% of the willow ptarmigan population in the area.4. The spatial distribution of hunting pressure was strongly dependent on the starting point of the hunters, and areas close to the base cabin were subject to most hunting activity. Areas furthest away, towards the border of the hunting area, experienced little hunting activity.5. Logistic regression showed that survival probability of ptarmigan was best predicted by distance from the cabin. Shot radio‐tagged birds lived closer to the cabin, and had twice as high hunting pressure in their home range, compared with surviving radio‐tagged birds.6. This method of obtaining quantitative data about human effort will have application in other studies when there is a need to quantify and analyse human effort on temporal and spatial scales.
Population spatial structure and migration of three butterfly species within the same habitat network: consequences for conservation
Authors: Baguette Michel , Petit Sandrine , Quéva François 
Published: March 2003

Summary 1. In this study we addressed the question of the generalization of population viability analysis by comparing migration of different butterfly species in the same habitat network. We compared (i) the population spatial structure and (ii) the migration between local populations in three butterfly specialist species living in the same habitat (chalk grassland) within the same habitat network (eight patches) at the same time. 2. For the three species, population structures within the study system were considered as metapopulations. However, their patch occupancy and migration patterns differed strongly, from a species with six small populations, one being apparently isolated (Cupido minimus), to a species with eight populations connected by individual movement with all others within the landscape (Melanargia galathea). 3. Patch area of both donor and receiver sites affected migration rate in M. galathea. Patch quality may interfere with this area effect in Aporia crataegi. Increasing distance between patches decreased both the probability of movements between local population and the number of moving butterflies. The distribution of migration distances differed between A. crataegi and M. galathea: this distribution followed an inverse‐power function for A. crataegi, and an exponential‐negative function for M. galathea. 4. These differences in population structure and migration patterns will have consequences for population viability analyses: the persistence of C. minimus cannot be expected if the habitat network is designed on the basis of the requirements of the two other species. Therefore, metapopulation persistence analyses have to remain species‐specific. As such analyses are impossible to perform on every threatened species living in a given habitat, we propose a preliminary screening of the most fragile candidate based on its population structure and mobility.