bluuebunny/crossref_metadata_2025_split huggingface dataset:
The population response to environmental noise: population size, variance and correlation in an experimental system
Authors: Benton T. G. , Lapsley C. T. , Beckerman A. P. 
Published: March 2003

summary

Variation in an organism’s environment can influence its life history and therefore its population size. Understanding the interplay between noise and population dynamics is of considerable importance, especially for prescribing management of economically important or threatened species. The impact of noise on population biology has been the subject of frequent theoretical investigations and discussed in posthoc analyses of time‐series. However, there is a dearth of experimental investigations.
Here we report results from a replicated laboratory study of soil mites, Sancassania berlesei, kept in controlled environments but with food supplied randomly, with different synchrony and variances, while maintaining the same mean rate.
Increasing environmental variance increases population variance, but decreases mean population size, therefore changing the observed shape of the distribution of population sizes: the shape becomes more skewed with more environmental variance.
The distribution of population sizes are best described by negative binomial or gamma distributions. Log‐normal and normal distributions rarely fit and Poisson distributions never fit.
The correlation between populations is sensitive to the correlation in environmental noise but insensitive to its variance.
Different life stages (eggs, juveniles and adults) respond differently to noise, in that there are significant differences in the way that environmental variation changes the mean, variance, shape of distribution and relationship between environmental and population synchrony.
Variability in interaction strength and implications for biodiversity
Authors: Kokkoris Giorgos D. , Jansen Vincent A. A. , Loreau Michel , Troumbis Andreas Y. 
Published: March 2003

Summary

We examined the species richness of theoretical communities in relation to interaction strength between species.
To do so, we used randomly constructed interaction matrices for competitive systems. To determine co‐existence, we tested for local stability and equilibrium feasibility of these theoretical assemblages.
As expected, we found that a low mean species interaction strength could allow for many species to co‐exist. However, variance in the interaction strengths may alter previous results; two systems with the same mean interaction strength show markedly different diversity depending critically on the magnitude of the variance. If species are similar enough then many can co‐exist, even if they compete strongly.
In addition we found that the species richness of a competitive community can greatly depend on the correlation between interaction strengths, an issue that so far has gone unreported. This correlation, a result of trade‐offs between species’ characteristics, may profoundly increase the potential for stable co‐existence of a highly species‐rich community.
Competition may not be an anathema to diversity. Statistical properties of species’ interactions may be critical factors that contribute to the explanation of species diversity in natural communities.
Factors affecting pup growth and survival in co‐operatively breeding meerkats Suricata suricatta
Authors: Russell A. F. , Clutton‐Brock T. H. , Brotherton P. N. M. , Sharpe L. L. , Mcilrath G. M. , Dalerum F. D. , Cameron E. Z. , Barnard J. A. 
Published: March 2003

Summary

We examined the relative importance of maternal, environmental and social factors for post‐weaning pup growth and survival in a co‐operatively breeding mammal, the meerkat Suricata suricatta .
Pup daily weight gain was primarily influenced by the number of carers per pup and the daily weight gain of those carers. Rainfall and daily temperatures had additional positive and negative effects, respectively, on weight gain of pups born to subordinates.
Pup overnight weight loss was primarily influenced by the amount of weight pups gained during the day, and their age. However, pups also lost considerably more weight overnight when temperatures were cold, although such effects were less in large groups.
Pup growth rates were positively influenced by the number of carers per pup and carer condition, and negatively influenced by high daytime temperatures.
Pup weight at independence was positively associated with weight at emergence and pup weight gain during provisioning, but negatively associated with the extent of overnight weight loss.
Pup survival between emergence and independence was related to maternal status, pup sex and overnight weight loss, as well as to group size, daytime temperature and monthly rainfall.
Thus, in meerkats, social factors largely, but not wholly, replace the importance of maternal factors that are commonly found to govern reproductive success in non‐co‐operatively breeding social vertebrates.
The impact of gastrointestinal nematodes on wild reindeer: experimental and cross‐sectional studies
Authors: Stien A. , Irvine R. J. , Ropstad E. , Halvorsen O. , Langvatn R. , Albon S. D. 
Published: March 2003

SummaryIt is well known that gastrointestinal nematodes can have a significant impact on the growth of farmed ruminants. The clinical signs of these parasites are often subtle, with production losses mainly due to reductions in host appetite and gut function. However, little is known about the impact of this widespread group of parasites on wild ruminants. We use experiments and cross‐sectional data to investigate the effects of gastrointestinal nematodes on a wild host, the Svalbard reindeer.Individually marked reindeer were treated for parasites. Their body mass, back fat depth and fecundity were compared with the control group one year later. The effect of treatment on worm burdens was investigated in a subsample of animals that were culled 3 and 6 months after treatment. Also, the relationship between the intensity of infection and body mass, back fat depth and host pregnancy rates was investigated in cross‐sectional data from culled reindeer.The anthelmintic treatment caused an increase in the body mass, back fat depth and fecundity of the reindeer. Treatment depressed the abundance of adult parasites ofOstertagia gruehnerifor at least 6 months, but had no significant effect on the abundance of adults of the other dominant parasite species,Marshallagi marshalli, or the abundance of larval stages of either species.In the cross‐sectional study, the probability of a reindeer being pregnant in late winter was negatively related to the abundance of adultO. gruehneriwhen controlling for host body mass. However, no clear evidence were found for an effect of parasitism on host condition in the cross‐sectional study.Our experimental results show for the first time in a natural ruminant host population that gastrointestinal nematodes can have a significant effect on host condition and fecundity. However, effects of infection on host condition was not detectable in the cross‐sectional study. Also, we show that the experimental effects on host condition and fecundity is most likely to be due to a negative effect ofO. gruehneri, while the experimental design did not allow detection of potential negative effects ofM. marshalli.
North Atlantic Oscillation timing of long‐ and short‐distance migration
Authors: Forchhammer Mads C. , Post Eric , Stenseth Nils CHR. 
Published: March 2003

SummaryThe timing of migration is associated with survival and reproductive risks of migrating species. Hence, variation in factors influencing this timing, such as climate, may have significant life history consequences for migrating species.Using an autoregressive phenological model, we analysed and contrasted the effects of climate (the North Atlantic Oscillation, NAO) and temporal dependence on the long‐term (1928–77) dynamics of springtime arrival in three long‐distance (83 populations) and three short‐distance (52 populations) migratory bird species breeding throughout Norway.Following high NAO winters both long‐ and short‐distance migrants arrived earlier than after low NAO winters. For long‐distance migrants, the effect of high NAO winters was probably indirect through improved forage conditions in winter quarters, whereas the effect on short‐distance migrants may be related both to improved forage and weather conditions during their northward spring migration. The NAO explained on average 13% (0–46%) and 18% (0–43%) of the interannual variation in arrival dates of long‐ and short‐distance migrants, respectively.For both migrant types, long‐term variability in springtime arrival increased with increasing strength of the influence of the NAO on timing of migration. In contrast, the strength of temporal dependence was unrelated to variability in long‐term springtime arrival.
Effects of sociality on short‐distance, female‐biased dispersal in tropical wrens
Authors: Yáber María Carolina , Rabenold Kerry N. 
Published: March 2003

Summary

Dispersal from the natal area, or between breeding sites, marks a critical transition for individual animals, and a fundamental demographic and genetic process. Limitations on dispersal in natural populations are important in predicting population dynamics and structure. Tropical habitats that can be naturally patchy are also being fragmented rapidly, and these habitats harbour many social species.
We studied dispersal in cooperatively breeding stripe‐backed wrens (Campylorhynchus nuchalis) in the Venezuelan savanna, using 20 years of data from marked populations over 40 km2. We test the hypotheses that dispersal is limited by competition for social position and that such limitation is sex‐specific.
Dispersal is strongly female‐biased, and results mainly in attainment of breeding status in neighbouring groups. Reproductive success is determined by the structure of the breeding group, and is concentrated in a small minority of individuals.
Natal dispersal is delayed, and represents a dramatic shift from indirect contribution to kin production (helping) to the direct approach of breeding. Monogamy limits breeding opportunities, compared to other social species, and both natal and breeding dispersal are constrained to short distances, particularly when compared to non‐cooperative breeders.
Males are more philopatric compared to females, for which more frequent and distant dispersal leads to greater reproductive success. Competition for breeding status in an established social order impedes dispersal, in part because experience and previous familiarity are important, particularly in males that rarely disperse to productive large groups.
Diverse patterns of sex bias in dispersal among cooperatively breeding birds can be explained by the comparative diversity of reproductive alternatives available to males and females. A ‘breeding diversity’ hypothesis is illustrated by comparison with male‐biased dispersal in brown jays.
Social resistance to movement establishes a brake on gene flow and demographic interaction among populations that has important implications for population viability.
Trends in the abundance of farmland birds: a quantitative comparison of smoothed Common Birds Census indices
Authors: Siriwardena Gavin M. , Baillie Stephen R. , Buckland Stephen T. , Fewster Rachel M. , Marchant John H. , Wilson Jeremy D. 
Published: March 2003

1.  Widespread declines in the populations of many British farmland birds have occurred since the early 1970s. We must understand the causes of these declines tomake recommendations about conservation and agricultural management, andthis can be approached by investigating the relationships, across species, betweenabundance and agricultural change. We describe novel, quantitative approaches to the interpretation of abundance indices from which reliable inferences about conservation status can be made. 2.  We calculated farmland Common Birds Census indices for 42 species, smoothed the series to reveal underlying trends and estimated confidence intervals for the changes in abundance. 3.  Between 1968 and 1995, the abundance of 12 species declined significantly andthat of 14 species increased. 4.  Specialization was the only significant determinant of changes in abundance (of 10 tests against species characteristics): 13 farmland specialists declined, on average, by 30%, whilst 29 more generalist species underwent an average increase of 23%, confirming that farmland birds should engender conservation concern. 5.  Smoothed abundance curves, transformed to emphasize trend direction and timing, were then compared quantitatively to identify whether groups of species had shared common trends. 6.  Species tended not to be strongly grouped, but small groups of species with common trends were identified. Similarities in ecology among grouped species clarify the possible environmental causes of their population trends, indicating future research priorities. 7.  The groups identified included: one group consisting of three thrush species Turdus and the skylark Alauda arvensis L. which all declined from the mid‐1970s after being stable previously; one group comprising three trans‐Saharan migrant warblers (Sylvidae), whose abundance fell in the early 1970s and later increased; and a diverse group of six smoothly increasing species. 8.  Turning points were identified as where each species’ population trend turned significantly, revealing critical periods during which populations are likely to have been affected by environmental change. 9.  Three collections of downward turning points were found, including one in the mid‐1970s when many farmland bird declines began. Four other periods each included many upturns. The groups of turning points should facilitate the identification of environmental changes which have had widespread effects. Management prescriptions can then be designed to reverse or to mirror such key changes and thereby focus conservation effort effectively.
Examining threats faced by island birds: a population viability analysis on the Capricorn silvereye using long‐term data
Authors: BROOK BARRY W. , KIKKAWA JIRO 
Published: March 2003

Summary

Population viability analysis (PVA) is widely used for assessing the extinction risk faced by endangered species and for evaluating the effects of potential management strategies. However, most PVAs are done in urgency and with limited data.
It is therefore important to know how the amount and quality of available ecological data affect the predictions of PVA. How can PVA results be interpreted when we have reliable, long‐term population data? When a species is endangered on islands, as are many endemic bird species, what are the likely causes of the decline, and what is the probable impact of new threats? This paper investigates these issues by modelling 26 years of monitoring data on the population of Capricorn silvereyes Zosterops lateralis chlorocephala Campbell & White of Heron Island on the Great Barrier Reef. Australia.
A PVA with parameters estimated from a relatively short (5‐year) period of data collection produced very different predictions of extinction risk compared with a PVA based on more comprehensive ecological data spanning 15–25 years. This indicates that caution should be exercised when using PVA as an indicator of absolute extinction risk.
Despite remaining viable over the past 26 years, the Heron Island silvereye population is predicted to be at risk of extinction within the next 100 years, with the magnitude of risk depending on the severity of impact of a range of potentially threatening factors. Increased mortality due to the introduction of new predators or diseases, inbreeding depression or frequent severe storms greatly increased the extinction risk. Habitat reduction, if not very severe, is unlikely to have a large impact. Similar threats and impacts may apply to other island bird populations.
Movement or dispersal between neighbouring islands had a mitigating effect on extinction probability and allowed extinct island populations to be re‐established. However, very small islands could only support sink populations that quickly became extinct and required an unrealistically high immigration rate to remain viable in the long term.
Temporal patterns of crop‐raiding by primates: linking food availability in croplands and adjacent forest
Authors: NAUGHTON‐TREVES LISA , TREVES ADRIAN , CHAPMAN COLIN , WRANGHAM RICHARD 
Published: March 2003

SummaryPrimates dominate lists of pests that damage crops around African parks and reserves. Beyond creating management problems, crop foraging is integral to the ecology of primates inhabiting forest—agriculture ecotones.Twenty‐three months of data from four villages around Kibale National Park, Uganda, revealed that redtail monkeysCercopithecus ascanius, olive baboonsPapio cynocephalusand chimpanzeesPan troglodytesselected different crops or plant parts. Baboons took root and tuber crops ignored by other primates, and fed on the greatest variety of crops. All three species preferred maize and/or bananas. Redtails ate only banana fruit, baboons ate banana fruit more frequently than pith, and chimpanzees raided pith and fruit in equal proportions.Each primate showed a distinct monthly pattern of crop foraging, significantly non‐random for baboons and redtail monkeys, weakly for chimpanzees. Large inter‐monthly variation was observed for all three primates, but was least pronounced in redtails.Raiding frequency on maize peaked approximately 8 weeks after the onset of rains and was strongly correlated between the three primate species. Abundant forest fruit did not diminish primate appetite for maize.Raiding frequency on bananas varied considerably despite continuous availability of fruit and pith. Peaks in banana consumption were unrelated to rainfall or maize raiding, but were associated instead with forest fruit shortages, specificallyMimusops bagshawei.Chimpanzees consumed banana pith more frequently when forest fruits were scarce, whereas baboons targeted more banana fruits. The use of banana pith by chimpanzees supports the suggestion that energy‐rich pith is crucial to chimpanzees during fruit scarcity.Conservation ofMimusops bagshaweiand other key forest fruit trees may lessen primate raiding intensity on perennial crops, e.g. bananas. Maize raiding appears unaffected by forest fruit abundance. Such highly palatable crops are best planted > 500 m from the forest edge.Planting agroforestry buffers along park edges creates ideal habitat for crop‐raiders. This management strategy is appropriate where human population density is low and crop raiding species are legal game. When dangerous or destructive wildlife species forage amidst densely settled subsistence farmland, managers are challenged to separate forests from agriculture using non‐palatable plant barriers or electric fences.
Squid stock fluctuations and water temperature: temporal analysis of English Channel Loliginidae
Authors: Robin J. ‐P. , Denis V. 
Published: March 2003

1. Monthly series of abundance indexes for the English Channel squid stock, based on fishery statistics of the United Kingdom (1980–93) and France (1986–96), were compared with water temperature data. The two objectives of the study were to test empirical predictive models and to analyse the stock–environment relationship at various time scales; both correlation and time‐series statistical techniques were applied. Sea surface temperature (SST) showed inter‐annual fluctuations and month‐to‐month auto‐correlation in addition to the annual cycle. 2. Trends in squid landings and temperature at the annual scale were found to be related, whatever the statistical method used (moving averages, cumulative functions or regression using averaged data). 3. Variable selection applied in a ‘multi‐month’ model suggested that fishing season indexes could be predicted from temperatures observed in the previous winter. The link between mild winter conditions and cohort success in winter/spring spawning species suggested that early life survival (and/or growth) was involved. This empirical model is a first step in the development of environment‐predicted recruitment indexes useful for management advice. 4. Seasonal decomposition was performed on both the squid resource data and SST data in search of short‐term relationships. In spite of the flexibility of the loliginid life‐cycle, no significant relationship was found between squid seasonally adjusted indexes and temperature anomalies in the previous months. This underlined the conclusion that temperature effect on cohort success was not constant throughout the year.
Densities of mammals in partially protected areas: the Katavi ecosystem of western Tanzania
Authors: Caro T. M. 
Published: March 2003

1.In Africa the majority of conservation areas sanction some sort of human activities within their borders but few of them are part of community‐based conservation schemes. The effectiveness of these state‐owned, partially protected areas in conserving mammalian fauna is largely unknown.2.Large and medium‐sized mammal densities in three different sorts of partially protected area were compared to mammal densities in an adjacent national park in western Tanzania by driving 2953 km of strip transects over a 14‐month period.3.In a Game Controlled Area that permitted temporary settlement, cattle grazing and tourist big game hunting, mammal diversity and mammal densities were relatively high. In a Forest Reserve that permitted limited hardwood extraction and resident hunting, most large species were absent. In a third, Open Area that allowed settlement, cattle grazing, firewood collection and beekeeping activities, mammal diversity and densities were again low but some large ungulates still used the area seasonally.4.The chief factors responsible for lowered mammal densities outside the Park were illegal hunting, especially in close proximity to town, and to a lesser extent, resident hunting quotas that were too high.5.These data suggest that state‐owned conservation areas permitting human activities within their borders cannot be relied upon as a means of conserving large and middle‐sized mammals in Africa.6.Two methods are being employed to ameliorate this problem in Africa: excluding people from conservation areas while upgrading ground protection effort, and initiation of community‐based conservation schemes. As yet, however, very few quantitative data are available to evaluate the efficacy of these methods in enhancing mammal populations.
On rate of increase (r): patterns of variation in Australian mammals and the implications for wildlife management
Authors: Hone* Jim 
Published: March 2003

Summary1. The annual rate of increase of a wildlife population is the change in abundance or density from one year to the next. This paper compares the expected and observed means and frequency distributions of annual instantaneous rates of increase (r) for unmanipulated field populations of the European rabbitOryctolagus cuniculus, red foxVulpes vulpesand house mouseMus domesticusin Australia.2. The observed meanrwas not significantly different from zero, the expected value, for each species, and the observed frequency distributions were not significantly different from the expected normal distributions.3. The observed distributions were used to estimate the threshold proportions of pests that need to be killed, harvested or sterilized to stop population growth. To stop maximum population growth, as can occur after large population reductions, the proportion to kill, harvest or sterilize ranged from 0·65 year–1for foxes to 0·97 year–1for house mice. It is recommended that the estimates are tested experimentally.4. The estimated proportions of pests to control were compared with extensive field data detailing attempts to control the pests. Estimated required levels of fox control were often less than observed levels of control. The required levels of rabbit and house mouse control could be higher than observed levels.