Importance of metapopulation dynamics to explain fish persistence in a river system

1. Habitat modification and fragmentation are key factors responsible for fish population decline worldwide. Previous assessments documented a total of 72 species extinctions for the sole class of Actinopterygii. However, global extinctions are difficult to monitor or study based on fossil records. By contrast, local extinctions occurring at the population level are easier to study. Given this context, an important question relates to whether extinction dynamics studied at the local scale can provide useful information to understand extinctions occurring at larger scales. This would be the case if local extinctions were not balanced by recolonisation as in a classic metapopulation. Our aim is thus to explain the observed regional (per basin) persistence of 252 fish populations by testing contribution of local extinction rates and more generally metapopulation dynamics components.
2. To address this aim, we used the annual extinction probability of 252 regional populations of up to 14 species inhabiting 18 coastal rivers, which became isolated c. 8,500 years ago. We specifically compared extinction probabilities obtained by seven theoretical models to investigate whether regional extinction rates (i.e. loss from a river system) were correlated to local extinction rates (i.e. loss from an occupied site) and the role of metapopulation dynamics to explain regional persistence.
3. Using empirical data, we showed the importance of variables related to metapopulation dynamics to explain extinction rates across the 18 river systems. As expected, the regional extinction rate decreased with the colonisation rate, area, metapopulation size, and percentage of occupied localities. By contrast, an inconsistent relationship emerged between regional and local extinction rates, as species with high local extinction rates were not particularly prone to regional extinction.
4. Our results provide strong support for the contribution of colonisation rates to explain persistence. Overall, our results show that the equilibrium number of occupied localities could be a good predictor of the long-term persistence of metapopulations in rivers. Finally, our results suggest the importance of connectivity to maintain sustainable populations within the river system.

     

Relating life‐history traits,environmental constraints and local extinctions in river fish

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Population fluctuations of mosquitoes in the non-seasonal tropics

Abstract.

• 1 Seasonal and annual fluctuations in abundance of a number of species of mosquitoes were studied in a relatively non-seasonal climate near Almirante, Panama.
• 2 The fluctuations observed were large, but did not have a period of 1 year and should be classified as non-seasonal.
• 3 At each site the various species were not synchronous in their fluctuation pattern, but the fluctuations of each species were synchronous over an area of at least 4 km long, in spite of large differences in habitat.
• 4 Changes in abundance from year to year observed in these mosquitoes are large compared with those of insects, including mosquitoes, in other areas of Panama.
• 5 The importance of such large and unpredictable fluctuations in abundance for planning control measures is discussed.

     

Species number, species abundance and body length relationships of arboreal beetles in Bornean lowland rain forest trees

ABSTRACT.

• 1 The relationships between number of species, abundance per species, and body length are examined for 859 species of beetles in samples of arthropods collected from ten Bornean lowland forest trees by insecticide fogging. Similar relationships are examined for different feeding guilds of these beetles, and for those beetles from different species of trees.
• 2 The data are used to construct four interrelated graphs, namely species: abundance, species: body length, population abundance: body length and total number of individuals: body length distributions.
• 3 In contrast to a number of previous studies, no consistent linear relationship between population density and body length was found for the Bornean beetles and it is suggested that, as in birds, the added dispersal ability of flight reduces critical population densities necessary for persistence in small species. Previous relationships between body weight and population abundance may also be artefacts of the way in which data were gathered.
• 4 Despite large samples, we failed to locate the mode in plots of the number of species in each abundance category (species: abundance distribution).
• 5 Species: body length and total number of individuals: body length plots were similar to those found in previous studies, although using data for Coleoptera alone may have produced a steeper decline in the total number of individuals as body size increases than is apparent in samples of all arthropods.
• 6 We present the first three-dimensional graph relating numbers of species, body lengths and population abundances. The surface of this three-dimensional relationship is relatively simple.

     

Logistic regression models for predicting occurrence of terrestrial molluscs in southern Sweden – importance of environmental data quality and model complexity

We compared the performance of four logistic regression models of different complexity with different environmental data quality, in predicting the occurrence of 49 terrestrial mollusc species in southern Sweden. Performance of models derived from an explanatory data set was evaluated on a confirmatory data set. The overall predictive success of our models (>80% for the three best model approaches), is as good as in other studies, despite the fact that we had to transform a text database into quantitative habitat variables. Simple models (no variable interactions), with forward selection, and detailed habitat data (from field visits) showed the best overall predictive success (mean=84.8%). From comparisons of model approaches, we conclude that data quality (map‐derived data vs habitat mapping) had a stronger impact than model complexity on model performance. However, most of these models showed relatively low values (mean=0.29) for Kappa (statistic for model evaluation), suggesting that the models need to be improved before they would be applied. Predictive success was strongly associated with species incidence but also Kappa was positively correlated with species incidence in univariate tests. Predictive success for true absences was negatively correlated with predictive success for true presences (R²=0.69) and most models failed to give a good prediction of both categories. Models for species with a high incidence in “Open dry sites” or “Mesic interior forests” had a better performance than expected, suggesting that occurrences of species with preference for “narrow” habitats are most easy to predict. Tree layer variables (openness and species abundance) were included in 48 of the 49 final predictive models, suggesting that these variables were good “indicators” of habitat conditions for ground‐living molluscs. Twenty‐four species models included distance to coast and altitude, and we interpret these associations as partly being related to differences in climate. In the final models, true presences (36.9% correctly classified) were much more difficult to predict than true absences (89.7% correct). Possible explanations might be that important habitat variables (e.g. chemical variables and site history) were not included. On the other hand, all suitable sites would not be expected to be occupied due to dynamics in local extinctions (meta‐population theory).     

Holocene mammal extinctions in the Carpathian Basin: a review

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Experimental tests of the role of predation in the population dynamics of voles and lemmings

• 1 Reasons for fluctuating populations of small mammals have been intensively investigated since the early days of modern ecology. Particular interest has been taken in vole populations exhibiting multiannual oscillations. Much empirical and theoretical work has been accomplished to find out the key factor(s) driving these population cycles and many reviews have been written about the results.
• 2 One of the most plausible processes for explaining regular fluctuations in small mammals is predation. Here I review the existing literature on the experimental studies of the role of predation in vole population dynamics in the hope that a critical examination of these studies will help researchers improve the design of future experiments.
• 3 Most predation manipulations have been done in exclosures, but there are also studies that have attempted to reduce or increase predator numbers in non‐fenced areas, islands and enclosures.
• 4 As the number of experimental studies has increased, their quality in terms of replication, use of controls and realistic spatial and temporal scales has also improved.
• 5 Most studies have found population‐level effects of predator manipulations on prey populations. The effects have varied from very weak to very strong, reflecting dissimilar experimental designs and the great variety of predator–prey interactions among different kinds of species in different landscapes. Most of these studies show that predation limits population growth of voles, and in some circumstances even regulate vole population fluctuations, but none of them clearly demonstrates that predation consistently changes fluctuation patterns of voles.
• 6 To be able to assess more reliably the true role of predation on (cyclic) population fluctuations of voles, more competent experiments are still needed not only over the geographical range of cyclic population dynamics, but also in areas of weakly or non‐cyclic populations of voles.

     

Effect of population density on reproduction of two sympatric dung beetle species,Aphodius haroldianus andA. Elegans (Coleoptera: Scarabaeidae)

The effect of population density on reproduction as well as the oviposition modes of two sympatric dung beetle species, Aphodius haroldianus (a low fecundity/high parental effort species) and A. elegans (a high fecundity/low parental effort species) was studied at a pasture in central Japan from 1982 to 1986.

1. The adult population density of A. haroldianus was high (>40 per dung pat). The density of A. elegans was low (<5 per dung pat). Oviposition of A. haroldianus was suppressed above the density of about 10 adults of conspecifics but not affected by the density of other species. The intra- and interspecific density effects on oviposition were not detected in A. elegans.
2. The number of A. haroldianus adults per pat decreased with dung age, while that of A. elegans increased until sixth day after deposition and then decreased. The number of eggs laid per pat was not different between 1-day-and 3-day-old pats for A. haroldianus. However, more eggs of A. elegans were found in 3-day-old pats than in 1-day-old ones.
3. In the both species, the amplitude of population fluctuations was not remarkable; the maximum/minimum ratio for five years being 2.3 for A. haroldianus and 2.9 for A. elegans. Different density dependent processes were suggested to function for the small fluctuation of population density between the two species, i.e. intraspecific density effect on oviposition for A. haroldianus and contest type competition for food among larvae of A. elegans.

     

Growth rates of phytoplankton under fluctuating light

• 1 The effect of light fluctuations on the growth rates of four species of freshwater phytoplankton was investigated. Experimental light regimes included constant irradiance and fluctuations of a step function form, with equal proportion of high (maximum of 240 µmol photons m^‐2 s^‐1) and low light (minimum of 5 µmol photons m^‐2 s^‐1) (or dark) in a period. Fluctuations of 1, 8 and 24‐h periods were imposed over several average irradiances (25, 50, 100 and 120 µmol photons m^‐2 s^‐1).
• 2 Growth rate responses to fluctuations were species‐specific and depended on both the average irradiance and the period of fluctuations. Fluctuations at low average irradiances slightly increased growth rate of the diatom Nitzschia sp. and depressed growth of the cyanobacterium Phormidium luridum and the green alga Sphaerocystis schroeteri compared to a constant irradiance.
• 3 Fluctuations at higher average irradiance did not have a significant effect on the growth rates of Nitzschia sp. and Sphaerocystis schroeteri (fluctuations around saturating irradiances) and slightly increased the growth rates of the cyanobacteria Anabaena flos‐aquae and Phormidium luridum (when irradiance fluctuated between limiting and inhibiting levels).
• 4 In general, the effect of fluctuations tended to be greater when irradiance fluctuated between limiting and saturating or inhibiting levels of a species growth‐irradiance curve compared to fluctuations within a single region of the curve.
• 5 The growth rates of species under fluctuating light could not always be predicted from their growth‐irradiance curves obtained under constant irradiance. When fluctuations occur between limiting and saturating or inhibiting irradiances for the alga and when the period of fluctuations is long (greater than 8 h), steady‐state growth‐irradiance curves may be insufficient to predict growth rates adequately. Consequently, additional data on physiological acclimation, such as changes in photosynthetic parameters, may be required for predictions under non‐constant light supply in comparison to constant conditions.

     

Use of hair tubes to survey for shrews: new methods for identification and quantification of abundance

• 1 Accurate and sensitive survey and monitoring methods are needed for shrews. We present a new design of hair tube and a new, simple method of species identification from multivariate analysis of four parameters measured from shrew guard hairs using a binocular microscope with incident light.
• 2 Multivariate analysis of these parameters measured from hairs of known identity showed that they can be used to identify hair to the species level with 85% accuracy.
• 3 We compared our indices of abundance from hair tubes (the hair tube index) with those from live trapping in 40 field margins. Capture‐mark‐recapture methods showed that capture rate did not vary systematically across sites, so that number of individuals captured was used as an index of abundance.
• 4 The hair tube index showed a significant association with the number of individuals captured for Sorex araneus and Neomys fodiens. The lack of a significant association for Sorex minutus may be because hair tubes are more sensitive in detecting this species than live trapping.
• 5 Hair tubes have additional advantages over live trapping, since they do not require frequent checking, are much lighter and cheaper than live traps, and no licence is required for their use in the UK. We therefore recommend consideration of their use in future surveys and monitoring studies of shrews. We provide an equation so that other researchers can use our multivariate method.

     

Mismatches between breeding phenology and resource abundance of resident alpine ptarmigan negatively affect chick survival

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The threat of invasive species to bats: a review

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The mammals of northern Melanesia: speciation,ecology, and biogeography

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A genomic assessment of population structure and gene flow in an aquatic salamander identifies the roles of spatial scale,barriers, and river architecture

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Effects of habitat size and isolation on species immigration–extinction dynamics and community nestedness in a desert river system

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Population cycles in voles and lemmings: state of the science and future directions

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The role of age of first breeding in modeling raptor reintroductions

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Voluntary recording scheme reveals ongoing decline in the United Kingdom hazel dormouse Muscardinus avellanarius population

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Anatomy of an outbreak: the biology and population dynamics of a Cardiaspina psyllid species in an endangered woodland ecosystem

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A preliminary study on collembolan populations in a pine forest

1. A study was made of the populations of Collembola in the pine forest. Among the eight species commonly found, Folsomia octoculataHandschin was numerically dominant.
2. Seasonal population changes of these eight species were described over a year. It was found that many species show two peaks in number. As for F. octoculata, the dominant species, the changes in number was discussed in connection with the variation in age structure.
3. The census data for each species were examined for the distribution pattern by using the regression method. None of these eight species was distributed at random in the soil and they could be classified into three groups based on the differences in the degree of aggregation in terms of coefficient β of the regression. It was suggested that such differences in the distribution pattern are largely due to differences in the response to heterogeneity of the habitat. In the case of F. octoculata, the changes of distribution pattern in the course of post-embryonic development were examined and it was found that (a) the component of distribution is a single individual rather than a colony, and (b) the degree of aggregation is decreased with the development of individuals.
4. Using the relationship, the relation of the necessary sample size to the population density was derived for a fixed level of presision (D=S.E./m=0.2) and some suggestions were given concerning sampling plans for these insects.