bluuebunny/crossref_metadata_2025_split huggingface dataset:
Predator behaviour and prey density: evaluating density‐dependent intraspecific interactions on predator functional responses
Authors: P. Anders Nilsson 
Published: September 2010

Abstract

In models of size‐structured predator–prey systems, the effects are evaluated of gape‐size limited predation on prey population growth and density when predators are non‐interacting, cannibalistic, interfering, and cannibalistic and interfering.
Predation from non‐interacting predators markedly reduces prey density, compared with prey densities in the absence of predation. When density‐dependent cannibalism between predators is introduced, predator density and therefore total functional response decrease, resulting in a decrease in predation pressure and higher prey densities.
Size‐ and density‐dependent interference between predators substantially decreases functional responses in the predators, and the prey population is thus allowed to grow more dense. Allowing for cannibalism between interfering predators also decreases predator density, but here the decreased number of predators does not have the releasing effect seen in solely cannibalistic predators. The interference between predators decreases with predator density, and per capita functional responses increase and compensate for the decrease in predator density.
These theoretical results are compared with results from natural systems with pikeperch and northern pike. Both species are cannibalistic, and pike are also kleptoparasitic, mirroring the models. Results from introductions of the different piscivores into natural systems corroborate the outcome of the models, since introduction or increased densities of pikeperch have shown to have severe and long‐lasting effects on prey, while pike have only initial, decreasing over time effects on prey stock. Thus, predator behaviour may seriously affect predator impact on prey, and size‐ and density‐dependent interactions between predators may be a major key to the understanding of predator–prey dynamics and community composition in lakes.
Non‐competitive phenotypic differences can have a strong effect on ideal free distributions
Authors: Ruxton Graeme D. , Humphries Stuart , Farnsworth Keith D. 
Published: September 2010

AbstractWe present a model of the ideal free distribution (IFD) where differences between phenotypes other than those involved in direct competition for resources are considered. We show that these post‐acquisitional differences can have a dramatic impact on the predicted distributions of individuals.Specifically, we predict that, when the relative abilities of phenotypes are independent of location, there will be a continuum of mixed evolutionarily stable strategy (ESS) distributions (where all phenotypes are present in all patches).When the relative strengths of the post‐acquisitional trait in the two phenotypes differ between patches, however, we predict only a single ESS at equilibrium. Further, this distribution may be fully or partially segregated (with the distribution of at least one phenotype being spatially restricted) but it will never be mixed.Our results for post‐acquisitional traits mirror those ofParker (1982)for direct competitive traits. This comparison illustrates that it does not matter whether individual differences are expressed before or after competition for resources, they will still exert considerable influence on the distribution of the individuals concerned.
A hidden cost of reproduction: the trade‐off between clutch size and escape take‐off speed in female zebra finches
Authors: Veasey Jake S. , Houston David C. , Metcalfe Neil B. 
Published: September 2010

AbstractThe concept of reproductive costs is a central tenet of life‐history theory, but the proximate mechanisms whereby such costs are mediated remain poorly understood. In this paper we demonstrate a link between clutch size and escape take‐off speed in small birds, mediated through changes in flight muscle volume during laying.In a series of experiments the same adult female zebra finches (Taeniopygia guttata) were made to lay both large and small clutches. When producing the larger clutches, females lost more flight muscle condition and became significantly slower to take off during escape flights.This reduction in take‐off speed with increased egg production was evident after the last egg was laid, and was independent of changes in body mass, so was not simply due to the presence of the eggs inside the female.This indicates that there is a trade‐off between fecundity and the maintenance of somatic musculature critical to an animal’s escape response. As changes in take‐off speed can have disproportionate effects on the chances of ground‐feeding birds surviving a predatory attack, the degree of reduction in flight muscle condition during laying could be a constraint on clutch sizes in such birds.
Effects of intra‐ and interspecific interactions on species responses to environmental change
Authors: Jeremy W. Fox , Peter J. Morin 
Published: September 2010

Abstract

The extent of directional environmental change expected in the next century underscores the need to understand density‐dependent population regulation.
Direct density dependence generated by intraspecific competition and/or predator–prey interactions should buffer environmentally produced changes in density‐independent growth rates (r). Density dependence generated by interspecific competition should magnify sensitivity to changes in r.
We tested these predictions by assembling protist communities in laboratory microcosms and subjecting the communities to directional environmental change. Two experiments used pairs of competing protists (Colpidium striatum Stein and Tetrahymena thermophila Nanney & McCoy, and Paramecium tetraurelia Sonneborn and Blepharisma americanum Suzuki) along with single‐species controls. Two experiments used predator–prey pairs (Didinium nasutum Müller or Euplotes patella Ehrenberg preying on Colpidium) and controls containing only prey. We grew replicates of each species combination in two temperature regimes (constant or slowly increasing temperature). Independent of these experiments, we quantified the temperature dependence of r (intrinsic rate of increase) for each species.
Comparison of effects of temperature on r to effects on mean density revealed that intraspecific competition buffered species densities against temperature changes that increased r by over 200%. Interspecific interactions did not affect species responses to environmental change. Temperature change had weak effects on species densities, whether or not other species were present.
The results suggest that natural populations, regulated by direct density dependence, may be buffered against directional environmental change. Environmental change will have large effects when populations experience little density dependence, and when environmental change has different effects on the vital rates of different species.
Site reoccupation in fragmented landscapes: testing predictions of metapopulation theory
Authors: Hames Ralph S. , Rosenberg Kenneth V. , Lowe James D. , Dhondt André A. 
Published: September 2010

Summary Populations of formerly continuously distributed species subdivided by habitat fragmentation may show distributions in space and time that are consistent with predictions of metapopulation theory. Local extinctions and recolonizations should result in the most fragmented sites being infrequently occupied and the least fragmented sites being continuously occupied by sensitive species. The probability of extinction is predicted to be negatively correlated with patch size and the amount of habitat in the landscape. Conversely, recolonization is predicted to be negatively correlated with the isolation of the patch, and positively correlated with the amount of habitat in the landscape. Data from a 3‐year study of the effect of fragmentation were used to test whether these predictions from metapopulation theory apply to populations of the long‐distance migrant forest birdPiranga olivacea(Scarlet Tanager) in fragmented North American landscapes. Principal components analysis was used to derive a composite measure of fragmentation. This measure was used in a logistic regression as a predictor of the number of years that territorial males would occupy a site, given that it was occupied at least once. More fragmented sites were more likely to be occupied only once; the least fragmented sites were more likely to be occupied in all three years. Data on fragmentation were necessary, but not sufficient, to predict site reoccupation, and were poor predictors at medium levels of fragmentation. The univariate measures of fragmentation (patch size and isolation, proportion of forest, and forest/non‐forest edge), were also used in logistic regressions to predict the separate probabilities of local extinction or recolonization. Local extinctions were negatively correlated with patch size and amount of forest in the landscape, as predicted. Recolonizations were negatively correlated with isolation of the patch as predicted, and surprisingly, also with the amount of edge in the landscape. This suggests that stochasticity may drive extinctions, but that habitat selection may play an important role in recolonization. Demographic data are usually required to establish the suitability of habitat to support persistent populations, but multiple‐year distributional data can provide information on habitat quality far above that obtained from single‐year studies.
Linking patterns in macroecology
Authors: Blackburn Tim M. , Gaston Kevin J. 
Published: September 2010

Summary Associated with the development of the field of macroecology has been the recognition and analysis of a number of different patterns in the large‐scale abundance and distribution of species. The mechanistic bases of these patterns have usually been considered in isolation, yet the patterns are necessarily linked, as the same individual animals contribute to all of them. Here, a model linking macroecological patterns in abundance, distributional extent and body mass is developed, based on how the finite amount of energy available to the species in a region is divided between them. The energy available to a species is assumed to support some quantity of biomass, which must then be allocated to either many small‐bodied or fewer larger‐bodied individuals. This identifies a necessary link between population size and body mass, which predicts when the variety of relationships between these variables in the published literature are expected to occur. Although framed in terms of energy use by species, the model does not assume that energyper seis necessarily limiting populations. How individuals use space determines the form of relationships between population size and distributional extent, distributional extent and body mass, and population density and body mass. The model additionally allows a number of falsifiable predictions about the anatomy of macroecological patterns. Support for the assumptions of the model is discussed.
Relative competitive ability does not change over time in blackbirds
Authors: Cresswell Will 
Published: September 2010

Summary Individual variation in feeding rate in the absence of competitors (absolute feeding rate) and decline in feeding rate in the presence of competitors (susceptibility to interference) are frequently used as measures of competitive ability or fitness in short‐term foraging studies. They are also crucial parameters of individual‐based population models that predict the distribution of animals across patches. There are, however, few data on whether absolute feeding rate and susceptibility to interference competition remain constant for individuals between years. The hypothesis that absolute feeding rate and susceptibility to interference were similar between years was tested by observing 25 European blackbirdsTurdus merulafeeding in seminatural experimental patches, during January to March over a 2–4‐year period 1995–98. Absolute feeding rate was measured as the feeding rates of solitary blackbirds. Susceptibility to interference was measured as the change in feeding rate of a focal bird when it fed in the presence of different numbers of competitors. Individuals changed significantly in their feeding rate between years, but most individuals did not change in their feeding rate relative to others in the population. The absolute feeding rate of an individual was significantly positively correlated with its feeding rate in the subsequent year. There was no significant variation in susceptibility to interference for individuals between years. Only two of 27 blackbirds showed a significant change in susceptibility to interference between years. Relative absolute foraging rate and susceptibility to interference competition were reasonably similar between years in blackbirds. Relative fitness measures derived from short‐term measures of foraging ability may therefore be valid over long periods. In ideal free models that incorporate individual competitive ability, rather than population averages, temporal changes in competitive ability can possibly be ignored.
Models of alternative life‐history strategies, population structure and potential speciation in salmonid fish stocks
Authors: Parker Henry H. , Noonburg Erik G. , Nisbet Roger M. 
Published: September 2010

Summary

High Arctic landlocked Arctic charr, Salvelinus alpinus L., are used as a reference system to examine the theory of alternative life history strategies in Salmonids and their implication for population structure and potential speciation. In these closed, autonomous systems, Arctic charr are the only fish species present and alternative life history strategies are represented by two distinct size modes, commonly known as ‘dwarf’ and ‘normal’ charr.
Simple mathematical models are used to caricature the density‐dependent interactions within and between the dwarf and normal components of these bimodal populations. Two different assumptions concerning the genetic relationship between the two alternative life history strategies are investigated: complete reproductive isolation, or a single stock which chooses between the alternative strategies facultatively.
In constant environmental conditions, the evolutionarily stable strategy (ESS) is not affected by the assumed genetic relationship, and the ESS proportions of dwarfs and normals are shown to depend on environmental parameters. The ESS proportions vary with these parameters along an evolutionarily stable continuum (ESC) and, in particular, a high proportion of normals is associated with high growth rate as a juvenile, and a ‘stunted’ or unimodal population with low growth rate. The predicted ESC for selection of the normal strategy is similar to that observed experimentally in the analogous case of smolting in Atlantic salmon, Salmo salar L.
A difference in the ratio of fecundity to mortality rate between dwarf and normal sub‐populations is shown to be essential to maintaining bimodal populations, and it is argued that cannibalism is one mechanism which could achieve this difference.
The model is extended to ask what ecological conditions would favour evolution toward the speciated or reproductively isolated state. It is concluded that short‐term environmental fluctuations select against speciation and it is speculated that most natural bimodal Arctic charr stocks will achieve maximum individual fitness within a ‘semispeciated’ configuration which is maintained by incomplete assortative mating.
Behavioural diversification in brook charr: adaptive responses to local conditions
Authors: McLaughlin Robert L. 
Published: September 2010

Summary

Recently emerged brook charr (Salvelinus fontinalis Mitchill) foraging in still‐water pools along the sides of streams exhibit conspicuous variation in foraging behaviour. Some charr are sedentary and eat crustaceans from the lower portion of the water column. Others are mobile and eat insects from the upper portion of the water column. This study examines whether this behavioural diversification represents potentially adaptive responses made by individuals to local environmental conditions.
Four models were constructed to predict how the ratio of mobile to sedentary charr was expected to change with pool morphometry, and how the location and orientation of mobile and sedentary charr were expected to differ within pools. The models assumed the charr forage competitively, but each model differed in assumptions regarding which features of pool morphometry determine the availability of the two main prey types. A spatial constraint hypothesis also was considered.
Findings from this study support the hypothesis that the divergent foraging tactics represent adaptive adjustments made by individual charr in response to competition for spatially separated food sources. Variation in the numbers of sedentary and mobile charr across pools, and spatial distributions of the charr and their crustacean and insect prey within pools, were most consistent with a model assuming that the availability of insect prey, and hence the number of mobile charr, was determined by the pool surface area while the availability of crustacean prey, and hence the number of sedentary charr, was determined by the pool perimeter.
Parallels between this pool system and polymorphic fish populations in larger lake systems identifies a potential link between the adaptive decision making of individuals and the spatial and phenotypic divergence of populations in response to spatial heterogeneity in food resources.
Habitat suitability and source–sink dynamics of beavers
Authors: Fryxell John M. 
Published: September 2010

Summary Theory suggests that territorial species should share many of the same dynamical characteristics as metapopulations, including asynchronous local dynamics, potential for stochastic extinction of the population when rates of successful dispersal fall below mortality risk, and critical importance of the ratio of suitable to unsuitable habitat for long‐term persistence. These propositions were tested on a population of beavers (Castor canadensisKuhl) in Algonquin Provincial Park, Ontario, which has been continuously monitored over 11 years. Results showed that the total population was considerably less variable than local abundance at 14 beaver colonies, due to asynchrony among local populations. This suggests that local ecological interactions were more important in determining year‐to‐year variation in beaver numbers than broad‐scale environmental processes, such as weather. Of the local colonies, 20% were never abandoned over 11 years, although there was considerable turnover among adults. Offspring production exceeded adult abundance at five source colonies, which did not quite compensate for negative net production at nine sink colonies. These observations were consistent with predictions of spatially structured models of territoriality incorporating local variation in habitat suitability. Mean colony size and probability of recurrence from year‐to‐year were associated with local food availability, indicating that trophic interactions were important in determining local population dynamics. The beaver population in Algonquin declined steadily over the study period, however, suggesting that spatial and demographic processes were insufficient to stabilize abundance over time. This is consistent with predictions of spatially structured models of territoriality in which suitable and unsuitable habitats are interspersed. It is hypothesized that long‐term decline in habitat suitability is induced by acceleration of woody plant succession due to selective foraging by beavers.
Adaptive precocial reproduction in voles: reproductive costs and multivoltine life‐history strategies in seasonal environments
Authors: Lambin Xavier , Yoccoz Nigel G. 
Published: September 2010

Summary

We determined whether reproductive costs associated with precocious or later breeding by female Townsend’s voles (Microtus townsendii) differ and how this relates to the multivoltine life history of microtines. We related the probability of mothers surviving the lactation period to maternal age and the number of pups per litter using logistic models allowing for a threshold value in either explanatory variable below (for litter size) and above (for age) which survival is constant.
Females born at the beginning of the breeding period were precocious, giving birth for the first time by the time they were 85 days old (min 38 days). Females born at other times delayed sexual maturation by up to 6 months.
The survival of females who gave birth before a fitted threshold of 85 days old declined precipitously if they gave birth to more than five pups per litter. Survival of older females did not vary in relation to the size of their litters.
Precocious females had not reached adult size when they conceived their first litter and substantially increased their structural mass during pregnancy. We estimated that young primiparous females gained on average 127 ± 9% of their conception weight during their 21‐day first pregnancy compared to an average increase of 47 ± 2% per pregnancy for all other females. It appears that the low survival during lactation experienced by this cohort alone may be a consequence of the cumulative costs of gestation, lactation and somatic growth.
We build simple life‐table models to estimate the contribution of very precocious (conception at 25 days), precocious (conception at 50 days) and non‐precocious females (conception > 50 days) to the population as the probability of surviving the spring and summer, plus the total number of females produced and surviving until the end of the summer. We parameterized such models using the empirical survival estimates. Females who conceived five young very precociously made the greatest contribution to the autumn population. Delaying reproduction had a large cost: a very precocious female starting with five young would contribute 7·21 females, while a precocious female with the same initial litter size would contribute only 2·83 females. This advantage stems from both the longer breeding‐life span and from the fact that offspring of very precocious females may themselves reproduce in the year of their birth, such that they compound the precocious investment of their mothers.
Thus iterated reproduction and the multivoltine nature of microtine life history select for cohort‐specific trade‐off between survival and reproduction.
Multiple predators in the pelagic: modelling behavioural cascades
Authors: FIKSEN ØYVIND , ELIASSEN SIGRUNN , TITELMAN JOSEFIN 
Published: September 2010

SummaryThe behaviour of predators is rarely considered in models of predator–prey interactions, nor is it common to include multiple predators in models of animal behaviour.We introduce a model of optimal diel vertical migration in zooplankton prey facing predation from two functionally different predators, fish and other zooplankton. Zooplankton predators are themselves subject to predation from larger zooplankton, and all zooplankton face the classical trade‐off between increasing growth rate and predation risk from fish towards the surface. Prey are most vulnerable to zooplankton predators at small sizes, but become more visible to fish as they grow. However, by habitat selection prey continuously manage their exposure to different sources of risk.We analyse situations with cascading behavioural interactions of size‐structured predator–prey interactions in the pelagic. In particular, we explore how vertical gradients in growth rates and relative abundance of fish and zooplankton predators affect optimal distribution patterns, growth and mortality schedules.A major model prediction is that prey susceptibility to one functional predator type depends on the abundance of the other predator. Higher abundance of zooplankton predators leads to risk enhancement from fish, minor increases in predation rate from zooplankton and unchanged prey growth rates. Increasing abundance of fish does not alter the risk from zooplankton predators, but reduces growth and development rates. Such asymmetric emergent effects may be common when prey and predators share the same spatial refuge from a common top predator.