What Shape Is the Relationship between Body Size and Population Density?

Geographic and bathymetric trends in abundance, biomass and body size of four grenadier fishes along the Iberian coast in the western Mediterranean

Population structure, in terms of the body mass, condition, sex and reproductive status of individuals, has been found to vary in phase with population density in cyclic populations of microtine rodents. Because sustained population cycles involve delayed density dependent changes in the population growth rate, we would expect at least some life history traits also to depend on past densities. Detailed, long‐term studies of changes in vole life history traits are however few, and are largely restricted to northern Europe. In view of the uncertainty as to whether the cyclic microtine populations of western Europe represent the same phenomenon as those of northern Europe, we studied temporal variation in the structure of a clearly cyclic population of the common vole Microtus arvalis Pallas, in the cereal plains of mid‐western France. Our data set contains seasonal, individual‐level data from long‐term, large‐scale trapping covering four entire population cycles. We found considerable cyclic variation in population structure in spring (April), but less so in summer (June). In spring of post‐peak years, animals were of low body weight and body condition (particularly females), litter sizes were smaller and there was a reduction in the proportion of breeders. All of these could be proximal drivers of increased mortality rates, or decreased birth rates, contributing to the population declines. Few life history traits, however, showed direct density dependent variation, and none of the traits studied here showed delayed density dependence. We have shown declines in the fecundity and body condition of voles from a western European population that coincides with, and may be a proximal cause of, cyclic declines in population density. Closer attention to proximal causes, by which ecological processes drive cycles, could clarify the extent to which microtine cycles across Europe represent a single phenomenon.

The worldwide extinction of large terrestrial mammals in the late Pleistocene has been attributed to climate change, overkill by human populations colonizing new continents, or some combination of these two processes. Lack of precision in chronologies for human colonization and mega- faunal extinction suggests that the role of overkill will be difficult or impossible to resolve from the archaeological and fossil record. In this study, we used a simple two species predator-prey model to examine the population density and hunting efficiency of a colonizing Aboriginal population necessary for overkill to have led to extinction (equilibrium density=0), of a range of different sized megafauna (250–1000 kg bodyweight) inhabiting an hypothetical tract of north Australian Eucalyptus savanna. We referred our modelling to this region because estimates of contemporary Aboriginal population density arguably set an upper limit for those occurring during the Pleistocene, and data are available on harvesting rates of large introduced mammals such as buffalo. Modelling results indicated a compensatory trade-off between the effect of Aboriginal population density and hunting efficiency (measured as the rate of effective search for prey) on equilibrium megafauna densities. The modelling also demonstrated that although intrinsic rate of population increase and density at carrying-capacity for mammals increase with declining body size, smaller megafauna would have been more readily exterminated than larger megafauna because they would have been harvested at a higher rate to satisfy the demand for meat. However, while at contemporary Aboriginal densities it appears plausible that over-harvesting could have affected the fate of smaller megafauna (<250 kg), hunting efficiencies required to drive medium (500 kg) and larger (1000 kg) sized megafauna to extinction appear unrealistically high. This conclusion would be reinforced if Aborigines were able to switch prey at low megafauna density, a contingency not considered in our model. Collectively, these results suggest that for overkill to have driven medium to large marsupial megafauna extinct in the northern Eucalyptus savannas, Aboriginal densities must have been considerably higher than contemporary levels, or Aboriginal hunters astonishingly efficient. Alternatively, climate change in the late Pleistocene may have played an important role in the extinction of Australian megafauna.

In an agroecosystem, catches of epigeal invertebrate predators obtained by pitfall traps were compared to absolute population densities estimated by ground photoeclectors in two different habitats, a field and an adjacent set-aside land. In general, abundance of Carabidae and Lycosidae were overestimated by pitfalls, while Staphylinidae and Linyphiidae were underestimated, and beetle larvae showed no obvious trend. The overestimation of Carabidae and Lycosidae by pitfalls had its maximum in spring and summer. Numbers collected by pitfalls did represent actual population densities better in the field than in the set-aside. This is probably caused by the higher vegetation diversity and complexity of the set-aside land which additionally influenced the catches. Pitfalls recovered higher numbers of animals and species, and species composition differed significantly between pitfalls and photoeclectors, in the field as well as in the set-aside. Body size seemed to be the main factor in determining the catch, the relatively larger species being more frequently caught by pitfall traps. In sum, the relationship between pitfall trap catches and actual population densities appeared to be either absent, weak or highly variable among taxa, habitat and time of the season. Thus numbers caught in pitfall traps cannot be considered as reliable indices of “real” abundance nor do they reflect the relative abundance within a given predator community correctly. Therefore, in most cases absolute density estimates should be preferred for the study of epigeal invertebrates in arable land. However, I suggest a combination of both pitfall traps and standardised area samples, because the two approaches possibly provide information of different qualities equally important for the evaluation of epigeal predator species, namely searching activity and population density.

Body size is a fundamental trait that impacts many aspects of species biology and ecology. It is, in turn, influenced by a suite of environmental factors, and often decreases with warming. Although environmental conditions can also impact body shape, which is another functional trait that influences locomotion, resource acquisition and potentially physiological processes, such responses are poorly understood and rarely quantified. We experimentally tested the independent and combined effects of environmental temperature, resource level and interspecific competition on the body shape and size responses of two model protist species. We also tested the degree to which these individual‐level phenotypic responses are associated with population densities and species coexistence. Body shape was strongly influenced by resource competition, whereas body size changes were mainly driven by environmental temperature. In both species, lower resource levels resulted in body shape elongation, suggesting that relatively more elongate individuals with potentially higher swimming speed were advantaged in the resource scarce environment. However, competition had contrasting influence on the body shape of the two species. Competition decreased the population densities of Blepharisma japonicum, which exhibited relative body shape elongation, similar to the response at low resource levels. In contrast, competition increased the population densities of Paramecium aurelia, which exhibited reduced elongation similar to body shape response at high resource levels. Hence, body shape responses could be indicative of changes in resource availability, aiding our understanding of competitive hierarchies and species interactions. Coexistence was observed in all treatment combinations, likely because body size of both species decreased similarly under warming, potentially maintaining constant per capita competitive intensity. These findings, along with recent research on phytoplankton, diverse pelagic invertebrates, and birds highlight the importance of body shape and morphology across different taxonomic groups. Hence, we call for body size and shape to be considered in concert when investigating ecological consequences of climate warming. A free Plain Language Summary can be found within the Supporting Information of this article.

Corticosterone regulation in house sparrows invading Senegal

Urbanized areas can impose selective pressures on insects which can be identified at the individual level based on animal physiological condition. Physiological condition can be measured from variables such as body size, body mass or energetic budget of individuals. We examined whether body mass, wing spot size and energy reserves (proteins, lipids and carbohydrates) were reduced as urbanization increases, using adults of two damselflies, Hetaerina americana and H. vulnerata, in Central Mexico. We used a Habitat Integrity Index to assess the degree of urbanization in our sampled sites, considering biophysical attributes and the impact of anthropogenic activities. We did not find relation of above individual variables with urbanization degree. These results support possible resilience of rubyspot damselflies in the face of radical changes such as urbanization. Our finding echoes other results in damselflies research.Implications for insect conservationOur results highlight the resilience of these damselflies species in the face of urban disturbances. Thus design cities considering not only requirements of humans is essential to promote the presence and conservation of these and other species of insects in cities.Graphical abstract

Our aim in this study was to verify the usefulness of the standardized uptake value (SUV) normalized by individual CT-based lean body mass (LBMCT) in application of PET response criteria in solid tumors (PERCIST).We retrospectively investigated 14 patients (4 male and 10 female) with malignant lymphoma who were undergoing chemotherapy. (18)F-FDG PET/CT examinations were performed before and after chemotherapy. The LBMCT was calculated by estimation of fat weight from CT data (from skull base to pelvis). The mean±standard deviation (SD) and the Bland-Altman plot were used for comparison among body weight, LBMCT, and LBM derived from a predictive equation (LBMPE). Indices for FDG uptake in the liver were: SUV, SUV based on LBMPE (SULPE), and SUV based on LBMCT (SULCT). Overall differences between the uptake values were analyzed by one-way ANOVA. If the ANOVA showed significance, differences between uptake values were investigated further by use of the Tukey-Kramer test. The mean values of body weight, LBMPE, and LBMCT were: 55.4±14.9 (39.0-112.0), 43.0±10.5 (31.3-75.2), and 35.3±9.8 (23.4-75.8) kg, respectively. There was a wide dispersion between LBMPE and LBMCT (differences, 7.6±3.6kg; 95% CI, 6.42-8.85). LBMPE was higher than LBMCT in all the cases except in Case 11. The mean uptake values significantly differed among SUV, SULPE, and SULCT (F=68.3, p<0.05). Whereas SULPE deviated from PERCIST criteria in seven patients, SULCT satisfied the criteria except in one case. These results suggest that liver SULCT is useful for application of PERCIST.

Removal sampling, sweepnet sampling, and visual count sampling conducted while walking at constant velocity through a field were used to sample populations of adults of five coccinellid species in plots established in spring wheat fields, Triticum aestivum L. Estimates of absolute population density obtained from two 20-min removal samples taken from each of six 5- by 5-m sub-plots per plot proved reliable and were used to convert estimates obtained from sweepnet sampling (180 sweeps per plot) and visual counts (36 min per plot walking at 10 m/min) into absolute estimates of population density. Population density estimates obtained by removal sampling were quite precise except for species with low capture efficiencies and low population densities.Crop plant growth stage influenced the numbers of beetles caught in sweepnet samples and was incorporated in regression models for converting sweepnet catch to absolute density. Values of R2 of regressions ranged from 0.51 to 0.90, depending on species. Visual counts were influenced by temperature and aphid density, and these variables were incorporated in regression models. Values of R2 for regressions relating visual counts to population densities ranged from 0.63 to 0.94, depending on species.

The estimation of living body mass from skeletal material can be a useful component of a forensic profile. Previously, forensic anthropologists have generally used body mass estimation equations derived either from the femoral head or from a combination of bi‐iliac breadth and stature. However, these equations were originally generated for use in archaeological or paleontological contexts, and therefore may not perform as well in modern sedentary populations. In particular, these equations may significantly underestimate body mass in overweight and obese individuals, which increasingly account for a greater percentage of living populations.Here, we present new body mass estimation equations derived from measurements of the knee in a modern sample of known body mass. This reference sample consisted of 110 living subjects who participated in the Baltimore Longitudinal Study of Aging. Mediolateral breadth measurements of the distal femur and proximal tibia were taken from anteroposterior radiographs of the knee, and used with recorded body weight to develop prediction equations. We compare the results from equations derived from the entire reference sample with equations derived from a sample that excludes obese individuals (BMI&gt;30). We also compare equations derived from youngest recorded body mass with equations derived from older body mass recorded at the time of x‐ray.R square, % standard error of the estimate, and % prediction errors are minimized in equations that use youngest recorded body mass and exclude obese individuals. Although body mass for obese individuals is underestimated by all equations, it is best approximated by equations derived from the older recorded body mass that include obese individuals. This type of equation also provides very good estimates of body mass for overweight individuals (25&lt;BMI&lt;30). All equations overestimate body mass to some extent in normal weight individuals, but equations derived from young adult body mass excluding obese individuals perform best in this group. Comparison with other studies suggests that certain of these equations may better approximate body mass in obese and overweight individuals than previously used equations.Our results indicate that, due to increasing rates of obesity in modern societies, body mass estimation equations designed for paleontological use should be applied with caution in the forensic context. Equations derived from modern samples with a greater proportion of overweight and obese individuals will perform better in such cases.

Evaluating presence and abundance of small carnivores is essential for their conservation. In Italy, there is scarce information on European pine marten distribution, and no data are published on its abundance. Camera traps have been widely used to estimate population density applying capture–recapture models for species in which individual recognition is possible. Here we estimate the abundance of European pine martens in central Italy using camera trapping and a model that allows the estimation of population density without the need for individual recognition Rowcliffe et al. (Anim Conserv 11:185–186, 2008). Camera trapping was also used to evaluate habitat use patterns by martens. Fifteen camera traps were deployed in 90 placements for 15 days each, for a total of 1,334 camera days. Pine martens were captured in 24% of camera trap placements with a mean trap success rate of 0.33 photographs per camera placement. Estimated pine marten population density in the study area was 0.34 individuals km−2. Marten trap rate was not strongly associated with any habitat type, although there were trends towards lower probability of records at locations with high coverage of cultivated fields and higher probability of records at locations with high coverage of human-made woodland. The results suggest that pine martens in this area are not confined to wooded habitat. To our knowledge, this study is the first application of the Rowcliffe et al. (Anim Conserv 11:185–186, 2008) method to a wild carnivore population and, furthermore, the first estimation of population density of pine martens in Italy.

In this paper, we describe a method for estimating animal population density per unit area from mark, release, recapture (MRR) data. Standard procedures are available for estimating population size from MRR data, but not density per unit area, which is often of more practical value. If data on dispersal movements are available in addition to capture/recapture records, they can be used to estimate the area over which the study population ranges. These area estimates can then be combined with MRR abundances to yield estimates of population density. As a concrete example of how these methods can be applied, we calculated population density estimates for seven MRR data sets for the screwworm, Cochliomyia hominivorax (Diptera: Calliphoridae), from Costa Rica. As a standard of comparison, we also used a different method to calculate estimates of screwworm density for five sets of USDA APHIS Screwworm Eradication Program data from Mexico. Mean densities for both sets of analyses were similar, ranging from 10 to 120 adult flies/km2. General agreement between the Mexican and Costa Rican estimates lends support to the dispersal approach we propose here. Although we have applied these methods to the screwworm as a specific example, they are entirely general and can be applied to virtually any organism for which both MRR records and dispersal data are available.

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The Population Density Tables (PDT) project at Oak Ridge National Laboratory (www.ornl.gov) is developing population density estimates for specific human activities under normal patterns of life based largely on information available in open source. Currently, activity-based density estimates are based on simple summary data statistics such as range and mean. Researchers are interested in improving activity estimation and uncertainty quantification by adopting a Bayesian framework that considers both data and sociocultural knowledge. Under a Bayesian approach, knowledge about population density may be encoded through the process of expert elicitation. Due to the scale of the PDT effort which considers over 250 countries, spans 50 human activity categories, and includes numerous contributors, an elicitation tool is required that can be operationalized within an enterprise data collection and reporting system. Such a method would ideally require that the contributor have minimal statistical knowledge, require minimal input by a statistician or facilitator, consider human difficulties in expressing qualitative knowledge in a quantitative setting, and provide methods by which the contributor can appraise whether their understanding and associated uncertainty was well captured. This paper introduces an algorithm that transforms answers to simple, non-statistical questions into a bivariate Gaussian distribution as the prior for the Beta distribution. Based on geometric properties of the Beta distribution parameter feasibility space and the bivariate Gaussian distribution, an automated method for encoding is developed that responds to these challenging enterprise requirements. Though created within the context of population density, this approach may be applicable to a wide array of problem domains requiring informative priors for the Beta distribution.

Summary1.Many animal species are detected primarily by sound. Although songs, calls and other sounds are often used for population assessment, as in bird point counts and hydrophone surveys of cetaceans, there are few rigorous methods for estimating population density from acoustic data.2.The problem has several parts – distinguishing individuals, adjusting for individuals that are missed, and adjusting for the area sampled. Spatially explicit capture–recapture (SECR) is a statistical methodology that addresses jointly the second and third parts of the problem. We have extended SECR to use uncalibrated information from acoustic signals on the distance to each source.3.We applied this extension of SECR to data from an acoustic survey of ovenbirdSeiurus aurocapilladensity in an eastern US deciduous forest with multiple four‐microphone arrays. We modelled average power from spectrograms of ovenbird songs measured within a window of 0·7 s duration and frequencies between 4200 and 5200 Hz.4.The resulting estimates of the density of singing males (0·19 ha−1SE 0·03 ha−1) were consistent with estimates of the adult male population density from mist‐netting (0·36 ha−1SE 0·12 ha−1). The fitted model predicts sound attenuation of 0·11 dB m−1(SE 0·01 dB m−1) in excess of losses from spherical spreading.5.Synthesis and applications.Our method for estimating animal population density from acoustic signals fills a gap in the census methods available for visually cryptic but vocal taxa, including many species of bird and cetacean. The necessary equipment is simple and readily available; as few as two microphones may provide adequate estimates, given spatial replication. The method requires that individuals detected at the same place are acoustically distinguishable and all individuals vocalize during the recording interval, or that theper capitarate of vocalization is known. We believe these requirements can be met, with suitable field methods, for a significant number of songbird species.