Vertebrate Population Dynamics Research Articles

Non‐linearity and Temporal Variability Are Overlooked Components of Global Vertebrate Population Dynamics

ABSTRACTAimPopulation dynamics are usually assessed through linear trend analysis, quantifying their general direction. However, linear trends may hide substantial variations in population dynamics that could reconcile apparent discrepancies when quantifying the extent of the biodiversity crisis. We seek to determine whether the use of non‐linear methods and the quantification of temporal variability can offer a more complete representation of changes in global population dynamics than commonly‐used linear approaches.MethodsWe analysed 6437 population time series from 1257 vertebrate species from the Living Planet Database over the period 1950–2020. We modelled populations through the use of second‐order polynomials and classified trajectories according to their direction and acceleration. We modelled and classified these same populations using a more classical linear trend analysis. We quantified temporal variability using the mean squared error of the fitted polynomials. We then used generalised linear mixed models to test potential sources of heterogeneity in non‐linear trajectories and temporal variability.ResultsIn all, 44.8% of the analysed population time series were non‐linear. Across all populations, 30% were declining, 30% were increasing, and 40% were with no linear trend. Among the population showing no linear trend, half were concave or convex. Non‐linearity was expressed differently between taxonomic groups, with mammals showing higher prevalence of non‐linearity. Marine and freshwater populations were more variable than terrestrial populations, and fish were more variable than other vertebrates. Differences between geographical regions were detected in both non‐linearity and temporal variability, but no straightforward pattern emerged. There were no differences in both components between IUCN categories.Main ConclusionsNon‐linearity and temporal variability reveal usually overlooked dramatic declines or recovery signals in global population dynamics. Thus, moving beyond linearity can improve our understanding of complex population dynamics and better inform conservation decisions. In particular, populations usually classified as ‘stable’ can hide informative changes in non‐linear and variability patterns that need to be considered in global biodiversity assessments.

Community composition and population dynamics of vertebrates in the State National Nature Park “Burabay”

The article presents the analysis results of vertebrate community composition in the State National Natural Park “Burabay” and its population dynamics for 2016–2020, as a basic component of the ecological network of specially protected natural areas, ensuring the conservation and restoration of biological diversity, both typical and unique landscapes. The route method of animal registration on the trial plot was applied to study and estimate the number of ungulates, carnivores, rodents, and guans. The animal life forms were classified according to the morphology of A.N. Formazov. The typical nature of the species composition of the park is confirmed by the presence of characteristic communities inherent in the steppe zone. The uniqueness of the species composition of vertebrates lies in the presence of species characteristic to the forest ecosystem; boreal relic animals; species of animals listed in the Red Book of Kazakhstan and species diversity.

Main Trends in Vertebrate Population Dynamics in the Clay Semi-desert of the Trans-Volga Region since the Mid-18th Century

The main natural changes related to the climate variations and the economic activities over the past 250 years in the area of the clay semi-desert along the interfluve between the Volga River and the Ural River have been considered. The authors define four climate periods based on humidity in the region: the mid-18th century to the 1820s, the 1830s to the 1950s, the 1960s to the end of the 1980s, and the 1990s to the 2010s. For each period, the area features related to humidity and human economic activities, which are followed by altering life for plants and animals in the region, are described. It is proven that only the existence and patterns of aquatic and waterfront communities are directly dependent on the climatogenic factors. Most changes in wildlife of the other communities reflect the impact of regional economic activities representing different stages and types, while the climate variations only adjust them. The ravine forests that existed in lake depressions until the 19th century could ensure the presence of a ravine-woodland complex in the regional fauna. After clearing these forests, a part of the ravine-woodland species complex completely disappeared from the region, some part became synanthropes, while others, once extinct from the region, then recolonized with the occurrence of polydominant woody-shrub thickets in lake depressions and afforested plains. A shift from a steppe vegetation formation to a desert formation across the plain occurred because of overgrazing during the dry season. Therefore, some steppe animal species also became extinct in the region, while the desert animals occupied the niches left vacant. Plowing of the flatlands caused the occurrence of wildlife species using the arable fields in the region as feeding habitats. Anthropogenic activities of various kinds contributed to the arrival of the range-shifting species.

Long-term variation in abundance of terrestrial mammals and birds in eastern Ecuador as measured by photographic rates and occupancy estimates

Long-term studies from undisturbed forests provide a baseline by which to assess impacts of human activities, including climate change, on vertebrate population dynamics in lowland tropical forests. We use cameratrap data from January to March, 2005 to 2015, to examine patterns of variation in numbers of images and occupancy (proportion of cameras where images of a species were obtained), variables that may reflect changes in abundance or activity patterns of terrestrial mammals and birds in an undisturbed lowland forest of eastern Ecuador. We accumulated 1,961 independent records of 31 mammal species and 427 images of 17 bird species during 5,547 trap-days. Number of mammal species ranged from 15 to 25 per year (107 to 466 images), whereas birds ranged from 3 to 11 species per year (10 to 122 images). Capture rates varied both among species and among years but showed no evidence of declines; populations of several species appeared to increase (Priodontes maximus, Dasypus novemcinctus, Pecari tajacu, and Dasyprocta fuliginosa). Similarly, occupancy rates provided no indication of consistent declines; occupancy rates increased significantly for D. fuliginosa, D. novemcinctus, and P. maximus. There was no indication that variation in either capture rates or occupancy was related to variation in large-scale climate trends as represented by the Southern Oscillation Index. Results suggest that populations of most species that are well sampled by camera traps have remained relatively stable over 11 years. Long-term studies from other regions in the tropics are needed to evaluate the generality of this pattern.

Hunting and Prey Switching by Chimpanzees (Pan troglodytes schweinfurthii) at Ngogo

Predation can have major effects on vertebrate population dynamics, including predator–prey cycles that occur on multiple time scales when predators switch between preferred and alternative prey and changes in the abundance of preferred prey when the availability of alternative prey changes. Predation has been an important selective force in primate social evolution and may regulate some primate populations, but assessing its impact is often difficult. Chimpanzees (Pan troglodytes) provide opportunities for direct collection of data on predation intensity by following habituated predators because they regularly prey on a variety of vertebrates, including other primates. Chimpanzees mostly hunt red colobus monkeys (Procolobus spp.) wherever they live in sympatry. Previous reports have documented heavy predation on red colobus by chimpanzees in the unusually large Ngogo community, in Kibale National Park, Uganda, and have shown an apparent decline in the local red colobus population. Here, we update information on predation at Ngogo, give further evidence of a red colobus population decline, and ask whether the chimpanzees have made more effort to hunt alternative prey in response. Data collected between 1995 and 2014 show that the rate of alternative prey hunts has increased significantly, while the rate of red colobus hunts has declined. Predation on red colobus peaked in 2002; other prey have since accounted for significantly higher proportions of hunts and prey captures. The overall hunting rate has not changed significantly, but per capita meat availability has decreased because hunts of alternative prey lead to fewer captures than hunts of red colobus. The likelihood that the chimpanzees hunt red colobus on encounter has not changed significantly. In contrast, the likelihood of hunting on encounter has increased (redtail monkeys, Cercopithecus ascanius; gray-cheeked mangabeys, Lophocebus albigena) or remained stable (guerezas, Colobus guereza) for other primates that are major alternative prey species. Encounter rates have not changed for redtails and mangabeys, but the guereza encounter rate has decreased. These results imply that the red colobus population is not recovering and raise the possibility that the chimpanzees are having a negative impact on the guereza population. Chimpanzees are not obligate carnivores, but this may make them prone to cause such impacts because their own populations are probably not limited by those of their prey.

Individual trophic specialisation and niche segregation explain the contrasting population trends of two sympatric otariids

Individual specialisation is increasingly recognised to be an ecological and evolutionary process having important consequences for population dynamics of vertebrates. The South American fur seal (SAFS) and the South American sea lion (SASL) are two otariid species with similar ecology that coexist in sympatry in the Uruguayan coast. These two species have contrasting trends and widely different population sizes. The underlying reasons for these population trends, unique in their geographical ranges, remain unknown. We studied the foraging ecology of these otariid species over 2 years at the individual- and population levels using the isotopic ratios (δ13C–δ15N) in whiskers of both sexes. We compared the isotope ratios between species and sexes and used several metrics to characterise the degree of overlap and distinctiveness in the use of isotopic niche space at the individual- and population levels. Interspecific trophic niche overlap was minimal, thus ruling out interspecific competition as the cause for the contrasting population trends of both species. At the intraspecific level, both species had sexual segregation in their foraging areas, but each species had a large overlap in the isotopic niches between sexes. While SAFS had a wider niche and generalist individuals, SASL had the narrower niche with a higher degree of individual specialisation. Behavioural constraints during the breeding season, intraspecific competition and a major dependence on resources of the Uruguayan coastal shelf may explain why SASL had a higher trophic individual specialisation and a larger vulnerability in a heavily exploited habitat by fisheries and, by consequence, a locally declining population trend.

Habitat use, bed‐site selection and mortality rate in neonate fallow deerDama dama

An understanding of mortality patterns, and especially the variation in juvenile mortality, is an important component in vertebrate population dynamics. Our study investigates, for the first time, neonate mortality and two levels of spatial behaviour, in a free‐ranging fallow deerDama damapopulation in southwestern Sweden. In the summers of 2008 and 2009, 36 fawns were marked with radio‐collars. Neonate mortality calculated by the Kaplan‐Meier method was 23.6%. Mortality caused by predation was low, since only one of eight non‐surviving fawns died from predation, probably by red foxVulpes vulpes. The spatial behaviour of the neonates was examined by habitat selection at home‐range level, which in fact is a selection made by the mother, and at bed‐site level within that habitat. Compositional analysis revealed a significant preference for arable land, pasture and coniferous forest between 5‐15 m high, compared to young forest. Selected bed sites showed significantly lower visibility and higher amount of canopy cover than random sites. Surprisingly, we did not find any relationship between canopy cover and visibility in selected bed sites while it showed a significant and negative relationship at random bed sites. We interpret this finding as while high canopy cover and low visibility covary at the habitat level, fawns seem to select these two bed‐site variables independently, perhaps for thermoregulatory reasons. Since there are few predators in our study area and predation pressure is low, this behaviour is not connected to actual survival rates in this area, but would rather be in support of the hypothesis of ‘pleiotropy’ as thermoregulatory reasons for bed‐site selection in neonate fawns might be the most important contemporary selection force in the absence of large predators.

Year‐round sexual harassment as a behavioral mediator of vertebrate population dynamics

Within‐species sexual segregation is a widespread phenomenon among vertebrates, but its causes remain a topic of much debate. Female avoidance of male coercive mating attempts has the potential to influence the social structure of animal populations, yet it has been largely overlooked as a driver of sexual separation. Indeed, its potential role in long‐term structuring of natural populations has not been studied. Here we use a comparative approach to examine the suitability of multiple hypotheses forwarded to account for sexual segregation (i.e., activity budget, predation risk, thermal niche–fecundity, and social factors) as drivers underlying sex‐specific habitat use in a monomorphic model vertebrate, the small‐spotted catshark, Scyliorhinus canicula. Using this hypothesis‐driven approach, we show that year‐round sexual habitat segregation in S. canicula can be accounted for directly by female avoidance of male sexual harassment. Long‐term electronic tracking reveals that sperm‐storing female catsharks form daytime refuging aggregations in shallow‐water caves (∼3.2 m water depth) and undertake nocturnal foraging excursions into deeper water (∼25 m) on most nights. In contrast, males occupy deeper, cooler habitat (∼18 m) by day and exploit a range of depths nocturnally (1–23 m). Males frequent the locations of shallow‐water female refuges, apparently intercepting females for mating when they emerge from, and return to, refuges on foraging excursions. Females partly compensate for higher metabolic costs incurred when refuging in warmer habitat by remaining inactive; however, egg production rates decline in the warmest months, but refuging behavior is not abandoned. Thermal choice experiments confirm that individual females are willing to “pay” in energy terms to avoid aggressive males and unsolicited male mating attempts. Long‐term evasion of sexual harassment influences both the social structure and fecundity of the study population, with females trading off potential injury and unsolicited matings with longer‐term fitness. This identifies sexual harassment as a persistent cost to females that can mediate vertebrate population dynamics.

Predation, individual variability and vertebrate population dynamics

Both predation and individual variation in life history traits influence population dynamics. Recent results from laboratory predator-prey systems suggest that differences between individuals can also influence predator-prey dynamics when different genotypes experience different predation-associated mortalities. Despite the growing number of studies in this field, there is no synthesis identifying the overall importance of the interactions between predation and individual heterogeneity and their role in shaping the dynamics of free-ranging populations of vertebrates. We aim to fill this gap with a review that examines how individual variability in prey susceptibility, in predation costs, in predator selectivity, and in predatory performance, might influence prey population dynamics. Based on this review, it is clear that (1) predation risk and costs experienced by free-ranging prey are associated with their phenotypic attributes, (2) many generalist predator populations consist of individual specialists with part of the specialization associated with their phenotypes, and (3) a complete understanding of the population dynamic consequences of predation may require information on individual variability in prey selection and prey vulnerability. Altogether, this work (1) highlights the importance of maintaining long-term, detailed studies of individuals of both predators and prey in contrasting ecological conditions, and (2) advocates for a better use of available information to account for interactive effects between predators and their prey when modelling prey population dynamics.

Towards a vertebrate demographic data bank

The development of computers, appropriate statistical methodology and specialized software has induced an explosion in empirical research on vertebrate population dynamics. Many long-term programs have led to impressive datasets and to the publication of hundreds of estimates of vital rates critical to many areas of ecology: evolution of life history strategies, conservation biology, behavioral ecology, population management, etc. Such estimates are still usually available through regular scientific articles, and their use for comparative purposes suffers from several shortcomings: duplication of technical work, lack of evaluation of methodological bias, and difficulties in linking vital rates estimates with other basic traits such as body size. It thus seems it is time to propose a demographic databank to collect the information on vertebrate demography published and being published and make it widely available. The resulting database should become the equivalent for vertebrate demography to what “Genbank” is for DNA sequences. Bird demography has a critical mass of knowledge adequate for a first step. This paper reviews, based on a prototype database, the outline of such a project of demographic database: type of data and estimates stored, assessment of methodology and data quality, data documentation, taxonomical and phylogenetical information, link with other existing biodiversity databases, procedures for depositing information, links with scientific journals, etc. The contours of a collaborative group to launch such a project are also discussed.

Demography of alpine red squirrel populations in relation to fluctuations in seed crop size

Vertebrate population dynamics, social organisation and space use often are closely associated with the distribution of critical resources, such as food. Tree squirrels are ideal models to study these relationships, since both key demographic parameters (reproduction, survival and dispersal) and spatio‐temporal variation in food supplies (measured as seed‐crop size) can be reliably estimated. In this paper we test the following two predictions underlying the association between annual food abundance and demography in six alpine red squirrel populations, both with and without time‐lag effects: 1) between‐season and between‐year fluctuations in survival rate, population density and increase parallel those in food availability; and 2) individuals follow a resource tracking strategy and increase in density mainly the year after a rich seed‐crop. Red squirrels occurred at higher densities in Scots pine forest, characterised by stable seed‐crops, than in Norway spruce with more abundant but more variable seed crops. Fluctuations in numbers were positively correlated with food availability, measured as annual conifer seed‐crop sizes. Overall, adult survival rates were higher than those of subadults, and survival substantially fluctuated between seasons and years. Autumn densities and rates of population increase (summer‐autumn) were strongly correlated with the same year's autumn seed‐crop, while correlations with the previous year's seed‐crop (time‐lag models) were either weak (population density) or absent (population increase). Results of this paper show that fluctuations in red squirrel densities in habitats with strong temporal variation in seed production are more closely linked with food availability than in more stable habitats. In addition, in the Alpine conifer forests squirrel population sizes, in autumn, increase in synchrony with food resources, eliminating the population lag normally present when resources are produced in pulses.

Dynamical and statistical models of vertebrate population dynamics

Population dynamics methodology now powerfully combines discrete time models (with constant parameters, density dependence, random environment, and/or demographic stochasticity) and capture–recapture models for estimating demographic parameters. Vertebrate population dynamics has strongly benefited from this progress: survival estimates have been revised upwards, trade-offs between life history traits have been demonstrated, analyses of population viability and management are more and more realistic. Promising developments concern random effects, multistate and integrated models. Some biological questions (density dependence, links between individual and population levels, and diversification of life histories) can now be efficiently attacked. To cite this article: J.-D. Lebreton, C. R. Biologies 329 (2006).

A long‐term study of non‐native‐heartworm transmission among coyotes in a Mediterranean ecosystem

In Mediterranean ecosystems, abiotic factors are known to affect vertebrate population dynamics, but little is known about how these factors affect population dynamics of parasites. We conducted a 9‐year investigation of the roles of temperature, precipitation, and vector abundance as determinants of transmission of the non‐native canine heartworm (Dirofilaria immitis), a dangerous parasite of pets, among coyotes (Canis latrans), an important reservoir, in north‐coastal California. Dates of heartworm transmission and total annual transmission were determined, respectively, from lengths and numbers of heartworms found in known‐age coyotes. Vector host‐seeking activity was assessed through weekly mosquito trapping. Within years, heartworm transmission occurred only when cumulative temperatures were sufficient to allow larval heartworms to develop to the infective stage (as predicted by an existing degree‐day model), and when suitable vectors were available. Most (95%) heartworms infected their hosts between 1 July and 14 September. The onset of transmission periods always occurred after the peak in vector host‐seeking activity and varied annually. Transmission periods ended before temperatures became limiting due to absence of vectors. The timing of host‐seeking activity of the primary vector species, Ochlerotatus sierrensis, also was correlated with the onset of warming temperatures such that parasite and vector phenology were synchronized. For this reason (partly), the variation in timing of seasonal warming had no detectable effect on total annual transmission. Abundance of host‐seeking Oc. sierrensis was positively correlated with annual precipitation, and annual heartworm transmission was positively correlated with abundance of host‐seeking Oc. sierrensis. Annual transmission also was positively correlated with abundance of a less numerous vector species, Anopheles punctipennis, and was directly correlated with precipitation. This study demonstrates that multiannual variability in temperature, which affects seasonality of transmission, has little effect on annual transmission, but that precipitation is a driving force determining annual transmission. These findings imply that in California, and possibly other Mediterranean climate zones, it is especially important to preventively treat pets in summers following high‐rainfall winters.

Signatures of large-scale and local climates on the demography of white-tailed ptarmigan in Rocky Mountain National Park, Colorado, USA.

Global climate change may impact wildlife populations by affecting local weather patterns, which, in turn, can impact a variety of ecological processes. However, it is not clear that local variations in ecological processes can be explained by large-scale patterns of climate. The North Atlantic oscillation (NAO) is a large-scale climate phenomenon that has been shown to influence the population dynamics of some animals. Although effects of the NAO on vertebrate population dynamics have been studied, it remains uncertain whether it broadly predicts the impact of weather on species. We examined the ability of local weather data and the NAO to explain the annual variation in population dynamics of white-tailed ptarmigan ( Lagopus leucurus) in Rocky Mountain National Park, USA. We performed canonical correlation analysis on the demographic subspace of ptarmigan and local-climate subspace defined by the empirical orthogonal function (EOF) using data from 1975 to 1999. We found that two subspaces were significantly correlated on the first canonical variable. The Pearson correlation coefficient of the first EOF values of the demographic and local-climate subspaces was significant. The population density and the first EOF of local-climate subspace influenced the ptarmigan population with 1-year lags in the Gompertz model. However, the NAO index was neither related to the first two EOF of local-climate subspace nor to the first EOF of the demographic subspace of ptarmigan. Moreover, the NAO index was not a significant term in the Gompertz model for the ptarmigan population. Therefore, local climate had stronger signature on the demography of ptarmigan than did a large-scale index, i.e., the NAO index. We conclude that local responses of wildlife populations to changing climate may not be adequately explained by models that project large-scale climatic patterns.

Could asynchrony in activity between the sexes cause intersexual social segregation in ruminants?

In many sexually dimorphic mammal species, the sexes live outside the mating season in separate social groups ('social segregation'). Social segregation occurs in a wide range of environmental conditions, but its cause in unknown. I suggest that social segregation is caused by a lower level of activity synchrony between individuals in mixed-sex groups than in single-sex groups, owing to sex differences in activity rhythm. As a consequence, mixed-sex groups are more likely to break up than single-sex groups, resulting in a predominance of single-sex groups at equilibrium. To test this hypothesis in red deer (Cervus elaphus L.), I developed an index of activity synchronization and showed that deer in mixed-sex groups were significantly less synchronized in their activity than deer in single-sex groups. Thus, low intersexual synchrony in activity can lead to social segregation. However, a lower level of intrasexual (female-female and male-male) activity synchrony within mixed-sex than within single-sex groups implies that additional factors (other than sex differences in foraging rhythm) contribute to the higher degree of instability of mixed-sex groups.

Diverse and Contrasting Effects of Habitat Fragmentation

Different components of an ecosystem can respond in very different ways to habitat fragmentation. An archipelago of patches, representing different levels of fragmentation, was arrayed within a successional field and studied over a period of 6 years. Ecosystem processes (soil mineralization and plant succession) did not vary with the degree of subdivision, nor did most measures of plant and animal community diversity. However, fragmentation affected vertebrate population dynamics and distributional patterns as well as the population persistence of clonal plant species. The results highlight the dangers of relying on broad community measures in lieu of detailed population analyses in studies of fragmented habitats.

Central Pacific Seabirds and the El Niño Southern Oscillation: 1982 to 1983 Perspectives

The breeding chronology and reproductive attempts of the seabird community on Christmas Island in the central Pacific Ocean (2 degrees N, 157 degrees W) were interrupted by the 1982-1983 El Niño Southern Oscillation. The resultant reproductive failure and disappearance of the entire seabird community of this equatorial atoll represents the most dramatic interruption on record of a seabird community located distant from coastal upwelling. Our data indicate the effect that the abiotic and biotic aspects of a global atmospheric-oceanic anomaly have on marine birds. The 1982-1983 El Niño Southern Oscillation provides an example of selective pressures and a natural experiment in the study of vertebrate population dynamics.

The Cost of Mating

The Cost of Mating

Vertebrate Ecology in Public Health

MY OBJECTIVE IS to indicate the scope and place of vertebrate in modem public health. Ecology is a term which has recently gained vogue; today an ecologist is almost never called upon to explain its meaning. Yet, because of the broad scope of the termencompassing all interrelationships between an organism and its environment-he usually finds it necessary to specify the branch of in which he has specialized. If one accepts the literal definition of ecology, nearly every worker in the biological or medical field can be considered an ecologist, for each is concerned with the relationships of organisms to their environment in one sense or another. A viral geneticist, for example, studies the effects of naturally occurring or purposeful changes in the environment upon the genetic characteristics of viruses. Similar examples can be drawn from practically any biological field, yet the workers in these fields rarely identify themselves a,s ecologists. The term can be applied far from its original intent, such as the ecology of thymus cells, and still be well understood. Actually, most people today think of as the study of an integrated system, the study of living organisms in situ. Traditional evolved from the study of natural history. The application of scientific methods to the already broad field of natural history brought about an inevitable fractionation. No single man can now hope to identify himself as simply an ecologist; he is either a plant ecologist or an animal ecologist. He also has major fields of interest, such as the effects of stress on the population dynamics of vertebrates or the effects of ionizing radiation on the phytoecosystem. In addition, ecological technique,s have become sophisticated. Foir example, lightweight, relatively powerful radio transmitters have been developed for the telemetry of physiological information from free-living wild animals, and the application of radiological techniques has created the whole new field of radiation ecology.