bluuebunny/crossref_metadata_2025 huggingface dataset:
The response of spotted hyaenas to long‐term changes in prey populations: functional response and interspecific kleptoparasitism
Authors: Höner Oliver P. , Wachter Bettina , East Marion L. , Hofer Heribert
Published: March 2003

Over the last three decades the main prey species (wildebeest Connochaetes taurinus, zebra Equus burchelli, Thomson’s gazelle Gazella thomsoni, and Grant’s gazelle Gazella granti) of spotted hyaenas Crocuta crocuta in the Ngorongoro Crater, Tanzania, substantially declined in numbers, whereas buffalo Syncerus caffer numbers increased strongly. This provided a ‘natural experiment’ to investigate how a generalist predator such as the spotted hyaena responds to long‐term changes in prey populations. Here we compare data on the feeding ecology of Crater hyaenas from the late 1990s (period II) with equivalent data from the late 1960s (period I).

Hyaenas showed strong hunting preferences for wildebeest calves and gazelle fawns during both periods I and II. Adult buffaloes, prey difficult to hunt for hyaenas, were rarely hunted in either period despite a large increase in buffalo numbers from period I to II.

Hyaenas exhibited a functional response to the changes in prey populations by killing more buffalo calves and adult wildebeest during period II, relatively easy prey categories for hyaenas to hunt.

The proportion of carcasses scavenged and acquired by kleptoparasitizing other predators increased from period I to II. This was facilitated by an increase in the relative number of lion kills available to hyaenas during the same period.

Hyaenas defended a similar proportion of their kills against kleptoparasitic attempts by lions during both periods. Since the ratio of kills hyaenas kleptoparasitized from lions in relation to kills lost to lions increased from period I to period II, hyaenas obtained more food resources from lions during period II than I.

The success of hyaenas kleptoparasitizing lions was influenced by the presence of male lions and the ability of hyaenas to recruit sufficient clan members to appropriate carcasses from lions.

This study is the first to demonstrate both a functional response of a predator to changes in the size of prey populations and an associated change in foraging behaviour of the predator.
Differential body condition and vulnerability to predation in snowshoe hares
Authors: Murray Dennis L.
Published: March 2003

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

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

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

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

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

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

1. 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

1. 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

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.
Intensity of parasitic nematodes increases with organochlorine levels in the glaucous gull
Authors: Sagerup Kjetil , Henriksen Espen O. , Skorping Arne , Skaare Janneche Utne , Gabrielsen Geir Wing
Published: March 2003

1. Organochlorines probably suppress immune functions in birds and mammals, but few field assessments are available. If establishment and/or survival of parasites is limited by host immunity, we would expect increased parasite intensities in animals with high organochlorine burdens, such as the glaucous gull Larus hyperboreus.

2. We collected 40 adult glaucous gulls on Bear Island in the western Barents Sea. Concentrations of nine selected polychlorinated biphenyls (PCB; 28, 52, 99, 101, 118, 138, 153, 170 and 180) and five chlorinated pesticides (hexachlorobenzene, oxychlordane, DDE, DDT and Mirex) were measured in the liver. The abundance of 12 species of intestinal helminths, including one trematode, six cestodes, four nematodes and one acanthocephalan, was determined.

3. After controlling for nutritional condition, no single parasite species was significantly associated with concentrations of PCB or chlorinated pesticides. However, the intensity of all nematodes grouped together was positively correlated with 10 of the 14 organochlorine concentrations measured. The strongest correlations were with p,p′‐DDT, Mirex, Σ9PCB, and PCB congeners 28, 118, 153, 138, 170 and 180.

4. Although correlative and collected in the absence of immunological data, these data do not refute the hypothesis that organochlorines might affect avian immune function.
The adequacy of collecting techniques for estimating species richness of grassland invertebrates
Authors: Standen Valerie
Published: March 2003

1. There is still considerable debate about the most effective methods of sampling invertebrates in monitoring and assessment programmes.

2. The above‐ground invertebrates of a limestone grassland in north‐east England were compared between samples from pitfall traps and from a D‐vac suction trap combined with a lightweight swish net (SW/DV).

3. Over 14 000 individuals were captured, with similar numbers in the pitfall and SW/DV samples. A total of 480 species of Hemiptera, Coleoptera, Diptera and Araneae was identified and placed into 14 taxa for further analysis.

4. The pitfall sample produced species/specimen curves from which it was possible to estimate species richness for all the Coleoptera and Araneae taxa and the calypterate Schizophora. The SW/DV sample was adequate to estimate the species richness of Hemiptera, most Diptera taxa, herbivorous Coleoptera and Linyphiidae.

5. The proportion of Coleoptera and Araneae taxa that were method‐unique was higher in the pitfall sample than the SW/DV sample and vice versa for the Hemiptera and Diptera taxa. Nevertheless, a relatively high proportion of method‐unique species of most taxa was found in both sample types, indicating that they can each contribute to assessing species assemblages in grasslands.

6. Both pitfall traps and SW/DV samples are needed to estimate species richness in grasslands for all taxa except Heteroptera, Homoptera and Lycosidae. Herbivorous Coleoptera and Linyphiidae were collected in numbers adequate for assessing richness in both sample types, but more specimens were required in one or other sample for the remaining taxa.
The impact of waterfowl foraging on the decomposition of rice straw: mutual benefits for rice growers and waterfowl
Authors: Bird J.A. , Pettygrove G.S. , Eadie J.M.
Published: March 2003

1. Recent legislation in California, USA, has restricted traditional open‐field burning of rice straw residues, leading farmers to adopt alternative methods of straw disposal such as post‐harvest flooding of rice fields. These changes may benefit wildlife because winter‐flooded fallow rice fields provide foraging habitat to migratory waterfowl. In turn, the foraging activity of waterfowl may help to increase rice straw decomposition, providing a reciprocal benefit to farmers. We examined the effects of waterfowl foraging activity on straw decomposition and nitrogen mineralization following rice harvest in a fallow flooded soil.

2.  Experimental plots (25 m2) were established on a silty clay soil and were subjected to two post‐harvest treatments: wet‐rolled or untilled. Mallard ducks Anas platyrhynchos were placed in one‐half of the experimental plots, following a split‐plot design, for a 3‐week period, at a density equivalent to 33 birds ha−1 over a season of 180 days to approximate regional abundance data.

3.  Waterfowl foraging activity increased residual surface straw decomposition by 78% in untilled plots and 18% in wet‐rolled plots compared with the respective unforaged plots. Average straw diameter in foraged plots was reduced to one‐third that of unforaged plots.

4.  Waterfowl foraging and field tillage reduced nitrogen (N) concentrations in the surface straw residue remaining at the end of the winter fallow period. Below‐ground organic residue was not affected by waterfowl foraging, indicating that ducks did not incorporate the straw. There were no apparent additions of carbon (C) or N to the soil as a result of waterfowl activity.

5. We conclude that waterfowl foraging can substantially increase straw decomposition in flooded, fallow, rice fields. Accordingly, rice producers should consider agronomic practices that attract waterfowl, such as winter flooding, to maximize the decomposition of rice straw residue. At the upper end of regionally observed waterfowl densities (at or near 33 birds ha−1 season−1) waterfowl foraging activity may alleviate the need for autumn tillage. Shallow flooded rice fields will also provide important winter habitat to migratory waterfowl, aiding wetland management and conservation efforts in the Central Valley of California.

6. These results provide an example of how a mutually beneficial solution can be achieved that provides needed waterbird habitat while concomitantly alleviating an agricultural problem.
Modelling the spatial dynamics of parapoxvirus disease in red and grey squirrels: a possible cause of the decline in the red squirrel in the UK?
Authors: Rushton S.P. , Lurz P.W.W. , Gurnell J. , Fuller R.
Published: March 2003

1.  A stochastic individual‐based model for simulating the dynamics of an infectious disease in sympatric red and grey squirrel populations is described. The model simulates the spread of parapoxvirus between squirrels in fragmented populations based on the dispersal of infected animals, the probability of encounters between individuals, exposure to the virus and subsequent mortality.

2.  The disease model was integrated with a spatially explicit population dynamics model that simulated red and grey squirrel populations in real landscapes, using habitat information held in a geographical information system. Latin hypercube sampling was used to create a range of realistic life‐history and infection scenarios and the model was used to investigate the dynamics of red and grey squirrels in Norfolk between 1966 and 1980.

3.  The model predicted that parapoxvirus, like interspecific competition, could have led to the extinction of the red squirrel in Norfolk. The results suggest that the red squirrel–grey squirrel–parapoxvirus interaction represents a system of apparent competition mediated by an infectious agent, as seen in other interactions between resident and exotic species.

4.  The need for further epidemiological research on the virus is emphasized. We believe that the combined effects on disease transmission of habitat, behaviour and grey squirrels acting as reservoir hosts will lead to a patchy prevalence and sporadic incidence of parapoxvirus disease in red squirrels and a more rapid local replacement by grey squirrels.

5.  These results have implications for conservation management of the red squirrel in the UK. Schemes in which animals are translocated or given supplementary feeding may enhance disease spread by bringing infected animals into contact with others.
The effects of fragmentation on fluctuating asymmetry in passerine birds of Brazilian tropical forests
Authors: Anciães M. , Marini M.Â.
Published: March 2003

1.  Fluctuating asymmetry (FA) refers to the difference between the right and left sides in characters that should otherwise be bilaterally symmetrical, but whose expression is affected by epigenetic stress during development. Forest fragmentation may promote an increase in FA in isolated populations, by either genetic or environmental stress. FA may function as a biomonitor index in conservation biology if increased levels were observed in populations from fragmented habitats.

2.  We tested the hypothesis that FA is higher in birds from small tropical forest patches than in large forest tracts. We measured wing and tarsus FA on mist‐netted birds from seven fragments and seven continuous areas from south‐eastern Atlantic rain forest in Brazil. We performed FA comparisons between fragments and control groups for the whole community, for individual foraging guilds and for the six most abundant species.

3.  Wing and tarsus FA were significantly greater in fragments than continuous areas for the whole community and were both negatively correlated with forest fragment size. Differences in FA varied among foraging guilds, being more evident for insectivorous species, especially those feeding in or near the understorey.

4.  FA levels increased significantly in forest fragments in at least one trait for five of the six most abundant species. There was no correlation between tarsus and wing asymmetries for the individuals of any species nor any difference between the degree of asymmetries of these characters.

5.  We suggest that FA is a useful tool to assess the effects of fragmentation on forest birds, and may be applied in monitoring neotropical birds. FA indices might be profitably developed, particularly in species most threatened by fragmentation effects and when investigated in different morphological characters.
The effect of dingo control on sheep and beef cattle in Queensland
Authors: Allen L.R. , Sparkes E.C.
Published: March 2003

Predation by dingoes Canis lupus dingo is regarded as a widespread problem by Australian livestock producers. This study examined five decades of historical data to evaluate the use and effect of dingo control on the distribution of sheep and beef cattle in Queensland.

In Queensland, dingo bounties were significantly more numerous in years with high sheep numbers but significantly less numerous in years with high beef cattle numbers. These relationships probably reflected the social and economic attitudes of the two producer groups to dingoes.

The relatively high impact that dingoes are perceived to have on sheep compared with beef cattle, the control techniques used by the two producer groups, and the intensity at which these techniques are applied, were the underlying causes.

Subsequent to the introduction of baiting using 1080 (sodium fluoracetate), there was an immediate decline in the use of strychnine, the number of dingo bounties presented for payment, and the number of dingo trappers employed by local governments in Queensland. However, these changes were confounded by a simultaneous decline in sheep numbers and dingo control effort.

Barrier fences and poisoned ‘buffers’ were compared for their ability to protect sheep from dingo predation. With few exceptions, sheep numbers declined or increased marginally within 50 km inside a dingo barrier fence or within a boundary between sheep and beef cattle production outside the dingo barrier fence. This contrasted to areas > 50 km from the dingo barrier fence or sheep/cattle boundary.

Both poisoned buffers and barrier fences could be equally effective at preventing sheep losses. However, buffers are best suited to open arid areas where large‐scale co‐ordinated baiting programmes are more feasible and where prey scarcity leads to increased bait consumption. We predict that sheep production outside the dingo barrier fence in Queensland will contract from the north and east. There is a case for re‐establishing a barrier fence in this area to prevent such contraction.

Co‐ordinated predator management, such as barrier fencing or aerial baiting, can protect sheep at a regional level. However, unless the financial burden of pest control is shared through a centralized scheme, sheep producers living along the boundary are likely to leave the industry or substitute cattle for sheep and the sheep‐production area will contract.

This paper cautions the use of bounties as a measure of relative abundance and illustrates how people’s perception of a pest and the type of livestock they produce can affect their level of control effort and the control methods they use.
Colonization of grassland by sown species: dispersal versus microsite limitation in responses to management
Authors: Coulson Sarah J. , Bullock James M. , Stevenson Mark J. , Pywell Richard F.
Published: March 2003

Diversification of species‐poor grassland often requires the introduction of desirable species by sowing seed. Little is known about the factors controlling the spread of introduced species, or how these interact with management. We determined whether management affected spread rates of two grassland species by modifying seed dispersal or seedling establishment.

 An experiment was set up in 1995 on a species‐poor grassland. It comprised five blocks, each with four treatments: (1) autumn grazed only; (2) cut July; (3) cut July and September; (4) cut July and aftermath grazed. Twenty‐two plant species were separately slot‐seeded into each treatment plot, providing discrete linear colonization foci.

 The mechanisms controlling spread were studied in two species: Rhinanthus minor, an annual with large seeds adapted for wind dispersal; and Leucanthemum vulgare, a perennial with small seeds with no obvious dispersal adaptations.

 Perpendicular spread of each species by 1998 was described well by a simple inverse power model. Rhinanthus had spread further in the hay‐cut treatments (2–4) than in the grazed treatment (1). Leucanthemum spread poorly in all plots, with no treatment effects.

 Seed dispersal from source slots was also described well by the inverse power model. Dispersal curves for Rhinanthus were much longer in the hay‐cut treatment (3) than in the grazed treatment (1), because more seed dispersed during hay cutting than before, and cutting dispersed seed longer distances. There was no dispersal by grazing animals. Dispersal showed directional effects: seeds travelled further in the prevailing wind direction before the hay‐cut and in the grazed treatment; dispersal by hay cutting was further in the cut direction than in the opposite direction.

 Leucanthemum showed poor dispersal, with no treatment effects, except that more seeds were dispersed in the grazed (1) than the hay‐cut (3) treatment.

 The establishment and survival of sown seeds showed no treatment effects for either species.

 Management effects on the spread of Rhinanthus reflected effects on dispersal, rather than establishment. Leucanthemum showed poor dispersal but good establishment in all treatments, suggesting its spread may also have been dispersal‐limited. Rhinanthus was positively affected by hay cutting because it set seed at the time of cutting, whereas Leucanthemum set seed later and cutting reduced its seed production.

 The results indicate that management of grassland to enhance the colonization of sown species might be best targeted at enhancing seed‐dispersal distances. Hay cutting can do this, but must coincide with seed set.
A plant trait analysis of responses to grazing in a long‐term experiment
Authors: James M. Bullock , Joe Franklin , Mark J. Stevenson , Jonathan Silvertown , Sarah J. Coulson , Steve J. Gregory , Richard Tofts
Published: March 2003

There are few long‐term experimental studies of plant community responses to changes in grazing intensity. Here we report species’ changes in a mesotrophic grassland after 12 years of a grazing experiment and relate these changes to species’ life‐history traits.

The experiment was set up in 1986 on an extensified species‐poor grassland in lowland UK. Treatments comprised sheep grazing vs. no grazing in winter, grazing vs. no grazing in spring, and two grazing intensities in summer, in a 2 × 2 × 2 factorial design with two replicate blocks.

Point quadrat surveys in 1998 showed responses to grazing treatments by 17 of the 22 most common species. Species showed different responses, many of which were specific to a grazing season. Community changes were similar under spring and winter grazing, but the heavier summer grazing had different consequences. Species richness was increased by spring grazing, decreased by heavier summer grazing and unaffected by winter grazing.

More species responded to treatments in the 1998 survey compared with a survey in 1990. Furthermore, the whole experimental grassland had changed between the surveys, probably as a result of falling soil fertility. The two dominant grasses had declined drastically and most other species had increased in abundance. Five new species were found in 1998.

Intensive surveys of dicotyledonous species in 1998 showed five of the 12 most common species had responded to grazing treatments. In most cases dicotyledonous species had increased in abundance under heavier grazing in one or more season, and species richness was increased by spring and winter grazing. Compared with a 1991 survey, the number of species responding to treatments had increased by 1998 and seven new species were found.

We tested whether species’ responses to grazing were linked to life‐history traits according to three hypotheses: that heavier grazing would disadvantage (i) species grazed preferentially, (ii) species less able to colonize gaps or (iii) more competitive species. Mechanisms differed among seasonal treatments. Responses to heavier summer grazing were linked strongly to gap colonization ability. Responses to spring and winter grazing were positively related to grazer selectivity, a surprising result that might be explained if selectivity was positively related to plant regrowth ability.

This study shows the need for long‐term experimental analyses of community responses to grazing as vegetation responses may develop over a long time. The traits analysis suggests it may be possible to predict changes in species composition under grazing through an understanding of the mechanisms of plant responses. Grassland managers require such information in order to manipulate grazing regimes to achieve, for example, diversification or weed control.
Quality of cavity microclimate as a factor influencing selection of maternity roosts by a tree‐dwelling bat,Chalinolobus tuberculatus, in New Zealand
Authors: Sedgeley Jane A.
Published: March 2003

Cavity quality is important for the productivity and survival of many species of tree‐dwelling wildlife. Intensive land management practices, such as logging and agriculture, frequently reduce cavity availability and potentially affect the long‐term viability of populations.

The New Zealand long‐tailed batChalinolobus tuberculatusselects roosts in small knot‐hole cavities with specific structural properties relative to available cavities. They also change roosts daily among a large pool of different roosts. Such behaviour is likely to makeC. tuberculatusvulnerable to human‐induced deterioration in roosting habitat.

This study represents a case study of the degree of sophistication sometimes required to assess availability and quality of roost sites, by testing whether roosts selected byC. tuberculatusalso have specific microclimates.

Selection for microclimate was demonstrated by comparing temperature and humidity inside unoccupied maternity roosts with available, apparently unused, knot‐hole cavities, large trunk‐hollows and ambient conditions.

Compared with ambient conditions, roost and available knot‐hole cavities had stable microclimates displaying only small ranges in temperature and humidity. Temperature inside cavities was lower than ambient temperature in the day and was warmer (and peaked) at night. Humidity in cavities was constantly high. Mean temperatures within trunk‐hollows (not known to be used byC. tuberculatus) were cooler than mean ambient and roost temperatures, and temperature ranges in hollows were large and fluctuated similarly to ambient temperatures.

Compared with available cavities and hollows, roost cavities had higher minimum temperatures, and maximum temperatures occurred significantly later in the day and continued for significantly longer. Humidity ranges were less and high humidity was maintained for longer.

The results suggest thatC. tuberculatusselects maternity roost sites with microclimatic conditions that are likely to accrue substantial energetic benefits. Predicted energy savings for adult bats using roost cavities compared with available knot‐holes were 1·1–3·3%, and compared with hollows 3·4–7·3%. Greater energy savings would occur at night and benefit non‐volant young.

In order to evaluate adequately and mitigate the full impacts of land‐use practices, there is a need for wider tests to provide direct evidence of interactions between habitat management, cavity provision and survival of cavity‐dependent wildlife.