bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mitigating human disturbance: can protection influence trajectories of recovery in benthic assemblages?
Authors: BEVILACQUA STANISLAO , TERLIZZI ANTONIO , FRASCHETTI SIMONETTA , RUSSO GIOVANNI FULVIO , BOERO FERDINANDO 
Published: June 2006

Summary

Understanding whether Marine Protected Areas (MPAs) can be considered as a suitable tool for restoring the structure and function of populations and assemblages is urgently needed to achieve an effective policy of mitigation of human impact in coastal management. However, to date, the role played by MPAs in enhancing ecosystems resilience has been more advocated than unambiguously documented.
This study was designed to test whether full protection in marine reserves facilitates recovery of benthos impacted by the date mussel Lithophaga lithophaga fishery, one of the most harmful human activities affecting subtidal rocky habitats in the Mediterranean Sea.
The effects of this destructive fishery were reproduced at one fully protected location (P) and at two unprotected control locations (Cs) in the SW Mediterranean Sea. At each location, three plots (4 m2) of rocky surface at 4–6 m depth were disturbed experimentally, while another three plots served as reference. In each plot, the species composition and relative cover of the sessile benthic assemblages were sampled photographically on each of five occasions during a period of 20 months.
Over and above variation in habitat features among locations, multivariate and univariate analyses revealed significant differences between P‐vs.‐Cs in patterns of assemblage recovery and showed that, at the fully protected location, recovery was faster than at the unprotected control locations.
Our results suggest that MPAs have the potential to change the trajectories of recovery of disturbed assemblages by accelerating the processes of recolonization and call for further investigation to identify the specific mechanisms underlying increased resilience.
Consequences of heterogeneity in survival probability in a population of Florida scrub‐jays
Authors: FOX GORDON A. , KENDALL BRUCE E. , FITZPATRICK JOHN W. , WOOLFENDEN GLEN E. 
Published: June 2006

Summary

Using data on breeding birds from a 35‐year study of Florida scrub‐jays Aphelocoma coerulescens (Bosc 1795), we show that survival probabilities are structured by age, birth cohort, and maternal family, but not by sex. Using both accelerated failure time (AFT) and Cox proportional hazard models, the data are best described by models incorporating variation among birth cohorts and greater mortality hazard with increasing age. AFT models using Weibull distributions with the shape parameter > 1 were always the best‐fitting models.
Shared frailty models allowing for family structure greatly reduce model deviance. The best‐fitting models included a term for frailty shared by maternal families.
To ask how long a data set must be to reach qualitatively the same conclusions, we repeated the analyses for all possible truncated data sets of 2 years in length or greater. Length of the data set affects the parameter estimates, but not the qualitative conclusions. In all but three of 337 truncated data sets the best‐fitting models pointed to same conclusions as the full data set. Shared frailty models appear to be quite robust.
The data are not adequate for testing hypotheses as to whether variation in frailty is heritable.
Substantial structured heterogeneity for survival exists in this population. Such structured heterogeneity has been shown to have substantial effects in reducing demographic stochasticity.
Census error and the detection of density dependence
Authors: FRECKLETON ROBERT P. , WATKINSON ANDREW R. , GREEN RHYS E. , SUTHERLAND WILLIAM J. 
Published: June 2006

SummaryStudies aiming to identify the prevalence and nature of density dependence in ecological populations have often used statistical analysis of ecological time‐series of population counts. Such time‐series are also being used increasingly to parameterize models that may be used in population management.If time‐series contain measurement errors, tests that rely on detecting a negative relationship between log population change and population size are biased and prone to spuriously detecting density dependence (Type I error). This is because the measurement error in density for a given year appears in the corresponding change in population density, with equal magnitude but opposite sign.This effect introduces bias that may invalidate comparisons of ecological data with density‐independent time‐series. Unless census error can be accounted for, time‐series may appear to show strongly density‐dependent dynamics, even though the density‐dependent signal may in reality be weak or absent.We distinguish two forms of census error, both of which have serious consequences for detecting density dependence.First, estimates of population density are based rarely on exact counts, but on samples. Hence there exists sampling error, with the level of error depending on the method employed and the number of replicates on which the population estimate is based.Secondly, the group of organisms measured is often not a truly self‐contained population, but part of a wider ecological population, defined in terms of location or behaviour. Consequently, the subpopulation studied may effectively be a sample of the population and spurious density dependence may be detected in the dynamics of a single subpopulation. In this case, density dependence is detected erroneously, even if numbers within the subpopulation are censused without sampling error.In order to illustrate how process variation and measurement error may be distinguished we review data sets (counts of numbers of birds by single observers) for which both census error and long‐term variance in population density can be estimated.Tests for density dependence need to obviate the problem that measured population sizes are typically estimates rather than exact counts. It is possible that in some cases it may be possible to test for density dependence in the presence of unknown levels of census error, for example by uncovering nonlinearities in the density response. However, it seems likely that these may lack power compared with analyses that are able to explicitly include census error and we review some recently developed methods.
The paradoxical effects of nutrient ratios and supply rates on an outbreaking insect herbivore, the Australian plague locust
Authors: CLISSOLD F. J. , SANSON G. D. , READ J. 
Published: June 2006

Abstract

The Australian plague locust, Chortoicetes terminifera, develops following rainfall in an environment dominated by two host plants, the annual Dactyloctenium radulans and the perennial Astrebla lappacea. This simple system provides an ideal opportunity to explore the relationship between plant quality, individual herbivore performance and population responses.
We compared the two grasses chemically and structurally, and the behavioural, physiological and developmental responses of locust nymphs to these diets.
The grasses appeared to be of similar nutritional quality in terms of their chemical composition, although they differed in their physical properties. Early instar nymphs performed equally well on both grasses. However, older nymphs consuming D. radulans developed faster, survived better and attained a higher body weight compared with those consuming A. lappacea.
The differences in performance by the older nymphs related to the rate and ratio of supply of carbohydrate and protein from the two grasses, with less carbohydrate being assimilated from A. lappacea than D. radulans per unit of protein assimilated. Experiments showed that these differences arose as a direct result of the physical barrier to nutrient extraction provided by cell walls and indirectly through the amount of water contained within each cell. Paradoxically, nitrogen did not limit performance in the traditional sense through shortage, but rather its relative excess in A. lappacea appeared to impede intake and assimilation of adequate carbohydrate.
As a consequence, we predict that the length of time D. radulans remains available following rainfall will influence plaguing dynamics, although not for the reasons previously thought.
The results highlight the need to consider nutrient balance and actual rates of supply (rather than simply measuring the chemical composition of the plant) when attempting to understand herbivore nutritional ecology.
Species richness and allometric scaling jointly determine biomass in model aquatic food webs
Authors: LONG ZACHARY T. , STEINER CHRISTOPHER F. , KRUMINS JENNIFER ADAMS , MORIN PETER J. 
Published: June 2006

SummaryAllometric theory makes specific predictions about how density, and consequently biomass, scale with organism size within trophic levels, across trophic levels and across food webs.Diversity–yield relationships suggest that more diverse food webs can sometimes support more biomass through mechanisms involving niche complementarity or selection effects that are sometimes attributed to organism size.We combine the above two approaches and show that, generally, density and biomass scale with organism size within and between trophic levels as predicted by allometric theory. Further, food webs converged in total biomass despite persistent differences in the composition and size of the organisms among food webs; species richness explained deviations from the constant yield of biomass expected from size–abundance relationships.Our results suggest that organism size plays only a transient role in controlling community biomass because population increases or decreases lead to rapid convergence in biomass. Species richness affects community biomass independently by effectively increasing the mass of organisms that can be supported in a given productivity regime.
Testing mechanisms of coexistence among two species of frugivorous primates
Authors: HOULE ALAIN , VICKERY WILLIAM L. , CHAPMAN COLIN A. 
Published: June 2006

Summary

We examined mechanisms of coexistence between two congeneric species of frugivorous primates, the blue monkey (Cercopithecus mitis) and the red‐tailed monkey (C. ascanius).
We used giving‐up densities (the amount of food which animals leave in a patch) in fruit trees to measure foraging efficiency and to evaluate possible mechanisms of coexistence. Animals with higher giving‐up densities are less likely to persist in the company of those with lower giving‐up densities because the former are not able to exploit food patches used previously by the latter. We climbed trees to estimate giving‐up densities by counting the fruit which primates left behind.
We tested five possible mechanisms of coexistence. Three mechanisms proposed that each frugivorous species has a lower giving‐up density than the other in at least one of the following: (1) different tree species, (2) within‐tree foraging zones or (3) seasons. The fourth mechanism predicted that the socially dominant species exploits resources first and that the subordinate species has lower giving‐up densities. The final mechanism predicted that one species would find resources more quickly than the other, which would in turn have a lower giving‐up density.
Four of the five mechanisms received no support from our data. Only a trade‐off between interspecific dominance and giving‐up densities was supported.
We discuss the generality of our results and possible interactions with other factors.
Spatiotemporal stability of two beetle populations in non‐farmed habitats in an agricultural landscape
Authors: BLACKSHAW ROD P. , VERNON ROBERT S. 
Published: June 2006

Summary

Understanding the spatiotemporal ecology of invertebrates in agricultural ecosystems is important for developing management strategies to enhance biodiversity and reduce pesticide use. There is increasing recognition that studies need to be undertaken at scales larger than the field but the ability to do this is often resource limited. Pheromone traps, developed for pest management, can provide a relatively cheap means of collecting data across wide geographical scales. In this study we used such traps to examine the spatial stability of two species of agrioted beetles in non‐farmed habitats over a period of 3 years.
The spatial distributions of adult male Agriotes lineatus and Agriotes obscurus were sampled from April until July at a number of sites across 950 ha on Westham Island, British Columbia, Canada. Data were assembled as spatially referenced cumulative trap counts by species and year, and analysed for evidence of aggregation and clustering using spatial analysis by distance indices (SADIE) methodology. Both intraspecific and interspecific association analyses were then carried out. A further set of analyses considered the spatial associations between different sampling dates in 2004.
Agriotes lineatus was clustered into patches and gaps at the landscape scale in all 3 years, and A. obscurus showed similar spatial structure in 2002 and 2003. For both species, spatiotemporal stability at the landscape scale was evident. There was also a positive association between the two species in 2 out of the 3 years, suggesting that they were responding in a similar manner to the landscape environment.
Synthesis and applications. This study showed that there was substantial temporal stability in the spatial structures of A. lineatus and A. obscurus in non‐farmed habitats, and that the two species respond in a broadly similar way to a heterogeneous agricultural landscape. This suggests that models to predict distributions within a landscape could be developed to guide decisions about where to grow vulnerable crops. Identification of the environmental factors that differentiate between clusters and gaps in their spatial distributions may also make it possible to manipulate populations and reduce their impact as pests without recourse to insecticides. Moreover, our results extend the spatial scales over which SADIE statistics have been used, and demonstrate the usefulness of pheromone trapping as a sampling method in addressing ecological questions at a landscape scale.
Sand dynamics in coastal dune landscapes constrain diversity and life‐history characteristics of spiders
Authors: BONTE DRIES , LENS LUC , MAELFAIT JEAN‐PIERRE 
Published: June 2006

SummaryIn fragmented landscapes where natural disturbance acts at the local level, community composition can be altered either by ‘species‐by‐species matching’, with community‐wide character displacement, or by ‘constrained species sorting’, whereby disturbance favours species with distinct ecological traits. It is necessary to understand such species shifts when aiming to detect bottlenecks associated with changing disturbance dynamics at different spatial levels. Such an understanding also provides insight into the underlying ecological mechanisms in operation and allows identification of species of conservation concern.This approach to understanding species’ shifts was applied to a study of spider diversity and life‐history variation in relation to sand dynamics in stabilized and dynamic grey dune landscapes located along the coasts of France, Belgium and the Netherlands.Local (α) diversity appeared to decrease with increasing local sand dynamics in both stable and dynamic landscapes. In dynamic dune landscapes, β‐diversity decreased significantly and approached regional (γ) diversity under local grey dune stabilization; in stabilized landscapes, β‐diversity was not affected by local sand dynamics.Comparative analyses of ecological traits revealed shifts in life‐history patterns, suggesting that patterns in local diversity resulted from species sorting. Species from fragments characterized by high sand dynamics showed narrower niche breadths, larger body sizes and longer generation times, while summer‐active species tended to become residential after sand stabilization. This provides evidence for constrained species sorting in which natural disturbance (through local sand dynamics) allows only species with distinct ecological traits to persist.Synthesis and applications. Species with larger body sizes, longer generation times and a higher degree of habitat specialization (i.e. related to dispersal ability) would be expected to be more vulnerable at dynamic sites and more prone to extinction than their counterparts from stabilized fragments. In particular, species with a burrowing lifestyle would be expected to go extinct locally as a result of increasing soil development and soil hardness. Shifts in species composition were found to be more pronounced in dynamic landscapes. Hence ensuring conservation of sand dynamics at a landscape level rather than at a local level is of prime importance when aiming to conserve typical psammophilous spider species within local assemblages in grey dune habitats.
The impact of variable hatching rates on parasite control: a model of an aquatic ectoparasite in a Finnish fish farm
Authors: FENTON A. , HAKALAHTI T. , BANDILLA M. , VALTONEN E. T. 
Published: June 2006

Summary

Many parasites of medical and veterinary importance infect via free‐living stages that undergo a period of development in the environment before seeking a host. Frequently, considerable variation is observed in the development rates of these stages, such that some individuals may be considered to occupy distinct subpopulations, similar to a plant's seed bank. Under certain conditions, these subpopulations may act as a reservoir for the parasite, buffering it from the impact of management strategies and reducing control success.
We assessed the impact of intraspecific variation in development rates on parasite control by developing a population dynamic model of the ectoparasite Argulus coregoni, a major parasite of Finnish fish farms. We divided argulid eggs into two subpopulations: an exposed class with fast hatching rates and an ‘egg bank’ with slower hatching rates. We then assessed the success of a number of potential control strategies under a range of egg bank hatching regimes.
The predicted seasonal dynamics of the various life‐cycle stages matched well those observed in Finnish fish farms. Simulations showed that the long‐term growth rate of the argulid population tends to be reduced by the presence of a slow‐hatching egg bank, unless the egg bank affords some protection in the form of reduced egg mortality.
Sensitivity analysis showed that the key stages of the parasite's life cycle are those that relate to the on‐fish juvenile mortality and development rates. The next most sensitive parameters relate to the number of viable eggs at the start of the year, such as female fecundity and overwinter egg survival. We showed that current control approaches that target these stages could prove highly effective at suppressing the argulid population. However, long‐term control was greatly reduced in both cases as the proportion of eggs entering the egg bank increased. This was especially true if mortality of the egg bank was lower than that of the exposed eggs.
Synthesis and applications. Understanding the factors affecting parasite persistence is vital for the development of effective long‐term control. We have shown that inherent heterogeneity within a parasite population may have a substantial impact on its long‐term growth rate, and can be an important mechanism reducing the effectiveness of targeted control strategies in the field.
Land management practices for combating desertification cause species replacement of desert lizards
Authors: HAWLENA DROR , BOUSKILA AMOS 
Published: June 2006

Summary

Patch structural complexity affects local species richness and population densities. Anthropogenic disturbance may alter complexity and heterogeneity, resulting in changes in community structure. Most studies in this area have dealt with human‐induced habitat degradation. We investigated a converse situation, in which anthropogenic activity increases productivity and complexity of an arid habitat.
Recently, large areas in the northern Negev Desert have been altered: a series of contour catchments was constructed to accumulate run‐off to support planted trees. We examined the effect of patch alteration by focusing on the lizard assemblage in the planted plots. Seven pairs of plots were established, one plot from each pair in a natural area and the other in an adjacent, altered slope. Lizards were captured using pitfall traps and environmental parameters were measured. To isolate the effects of trees as perches for avian predators, we ‘planted’ artificial trees in a loess plain and investigated the effect on an endemic lizard.
The structure of the lizard assemblage in the planted plots differed from that of the natural plots. Planted plots had a higher proportion of Mediterranean lizards and fewer desert species. Two local lizard species disappeared from the mosaic area of planted and natural plots. In addition, avian predators spent longer time in the artificial tree plots and reduced the lizard density compared to the natural plots.
The modification to the habitat generated only moderate changes in structure of the natural vegetation and this could not account for the observed changes in the lizard assemblage. Changes in the spatial use of the plots by avian predators was identified as the mechanism behind the observed distribution of lizard species.
Synthesis and applications. We argue that anthropogenic habitat modifications such as afforestation, urbanization, etc., can induce indirect biotic effects that may change the way and the scale at which different species respond to the habitat change. Such structural alteration may lead to species replacement and even to local extinction of specialist species. In order to protect biodiversity during large‐scale management projects, alteration of biotic interactions should be considered in advance and large unaltered patches should be protected, otherwise indirect effects might cause greater impacts than the structural manipulation itself.