Predicting changes in the Antarctic krill, Euphausia superba, population at South Georgia

Variability in the Southern Ocean is frequently reflected in changes in the abundance of Antarctic krill Euphausia superba and subsequent effects on dependent predators. However, the nature and consequences of changes in krill population dynamics that accompany fluctuations in its abundance are essentially unknown. A conceptual model, developed from quantitative measures of krill length in the diet of predators at South Georgia from 1991 to 1997, allowed predictions to be made about the abundance and population structure of krill in 1998 and the consequences for predators. Consistent with model predictions, in 1998 there was a serial change in krill population structure, low krill biomass and low reproductive performance of predators. The change in the modal size of krill, from 56 mm in December to 42 mm in March, was apparently a result of the transport of krill into the region. This is the first occasion when the future status and structure of the krill population at South Georgia has been successfully predicted. By representing local krill population dynamics, which may also reflect large-scale physical and biological processes, predators have a potential key role as indicators of environmental variation in the Southern Ocean at a range of spatial scales. Received: 6 March 1999 / Accepted: 3 September 1999     

Sink populations in carnivore management: cougar demography and immigration in a hunted population.

Carnivores are widely hunted for both sport and population control, especially where they conflict with human interests. It is widely believed that sport hunting is effective in reducing carnivore populations and related human-carnivore conflicts, while maintaining viable populations. However, the way in which carnivore populations respond to harvest can vary greatly depending on their social structure, reproductive strategies, and dispersal patterns. For example, hunted cougar (Puma concolor) populations have shown a great degree of resiliency. Although hunting cougars on a broad geographic scale (> 2000 km2) has reduced densities, hunting of smaller areas (i.e., game management units, < 1000 km2), could conceivably fail because of increased immigration from adjacent source areas. We monitored a heavily hunted population from 2001 to 2006 to test for the effects of hunting at a small scale (< 1000 km2) and to gauge whether population control was achieved (lambda < or = 1.0) or if hunting losses were negated by increased immigration allowing the population to remain stable or increase (lambda > or = 1.0). The observed growth rate of 1.00 was significantly higher than our predicted survival/fecundity growth rates (using a Leslie matrix) of 0.89 (deterministic) and 0.84 (stochastic), with the difference representing an 11-16% annual immigration rate. We observed no decline in density of the total population or the adult population, but a significant decrease in the average age of independent males. We found that the male component of the population was increasing (observed male population growth rate, lambda(OM) = 1.09), masking a decrease in the female component (lambda(OF) = 0.91). Our data support the compensatory immigration sink hypothesis; cougar removal in small game management areas (< 1000 km2) increased immigration and recruitment of younger animals from adjacent areas, resulting in little or no reduction in local cougar densities and a shift in population structure toward younger animals. Hunting in high-quality habitats may create an attractive sink, leading to misinterpretation of population trends and masking population declines in the sink and surrounding source areas.     

Mountain environment and population in Georgia: case study of Upper Svaneti

The purpose of the presented research is to identify local community opinions toward ecological problems in one of the mountainous region of Georgia (Upper Svaneti), to analyze how population ‘perceive, experience, and interpret’ the social, and ecological issues.

The paper is based on the results of Upper Svanet ipopulation’s survey which was carried out by the authors of presented paper during the August of 2015 and 2016.The questionnaire was elaborated taking into account the peculiarities of the region. Stratified-cluster selection method was used for selection of respondents and database compilation. For statistical analysis of polling data the SPSS package was used.

Based on the statistical analysis of survey results, the following issues have been studied: the most important ecological problems, environmental problems with respect to socio-economic ones, information sources on ecological problems, people’s trust in environmental issues, awareness level of the population on environmental policy, their personal contribution in environmental protection, ways to solve ecological problems, implemented environmental measures.

The obtained results are important to foster mountain population’s active participation in processes that contribute to decision-making processes, planning and implementing programs for sustainable development.     

Making a stand: five centuries of population growth in colonizing populations of Pinus ponderosa

The processes underlying the development of new populations are important for understanding how species colonize new territory and form viable long-term populations. Life-history-mediated processes such as Allee effects and dispersal capability may interact with climate variability and site-specific factors to govern population success and failure over extended time frames. We studied four disjunct populations of ponderosa pine in the Bighorn Basin of north-central Wyoming to examine population growth spanning more than five centuries. The study populations are separated from continuous ponderosa pine forest by distances ranging from 15 to >100 km. Strong evidence indicates that the initial colonizing individuals are still present, yielding a nearly complete record of population history. All trees in each population were aged using dendroecological techniques. The populations were all founded between 1530 and 1655 cal yr CE. All show logistic growth patterns, with initial exponential growth followed by a slowing during the mid to late 20th century. Initial population growth was slower than expectations from a logistic regression model at all four populations, but increased during the mid-18th century. Initial lags in population growth may have been due to strong Allee effects. A combination of overcoming Allee effects and a transition to favorable climate conditions may have facilitated a mid-18th century pulse in population growth rate.     

Finding regulation among seemingly unregulated populations: a practical framework for analyzing multivariate population time series for their interactions

The structure of ecological communities is often thought to be strongly influenced by population interactions. The interactions are often labeled as bottom-up and top-down control. Previous approaches to identify these processes often assume each population in the community is itself regulated. Therefore, each time series follows a stationary process. However, complex community structure and a lack of regulation in an individual population can result in inappropriate inferences based on traditional statistical approaches. Here, we introduce a statistical framework to analyze potentially non-stationary time series that are collectively regulated. We demonstrate the method with catch-per-unit-effort time series data of selected populations in the Gulf of Mexico. In the Gulf, we found that most of the time series data, which span 26 years, were non-stationary, thus individually unregulated. Species interaction patterns were location-dependent, but where brown shrimp interacted significantly with other species, we identified significant bottom-up forcing. On the other hand, we find almost no evidence of top-down forcing throughout the study areas.     

Upwelling-generated plankton strandlines: important predictable food sources for seabirds at Husvik,South Georgia

Sustained strong offshore winds generate upwelling in the fjords of northern South Georgia. Deepwater plankton is pumped by upwelling towards sandy beaches at the heads of the fjords; calanoid copepods, chaetognaths and pteropods are stranded by the sand filter in large quantities on falling tides. Local benthonic species (harpacticoid copepods and amphipods) are present in the plankton but do not strand. Strandlines are very rich (<4 kg wet mass m^-2) and provide large fractions of the food of kelp gulls, sheathbills and terns in the austral summer. Birds can only exploit fresh strandlines, since air-drying of the plankton soon makes it too salty to eat.     

Are penguins and seals in competition for Antarctic krill at South Georgia?

The Antarctic fur seal (Arctocephalus gazella) and macaroni penguin (Eudyptes chrysolophus) are sympatric top predators that occur in the Southern Ocean around South Georgia where they are, respectively, the main mammal and bird consumers of Antarctic krill (Euphausia superba). In recent years the population of fur seals has increased, whereas that of macaroni penguins has declined. Both species feed on krill of similar size ranges, dive to similar depths and are restricted in their foraging range at least while provisioning their offspring. In this study we test the hypothesis that the increased fur seal population at South Georgia may have resulted in greater competition for the prey of macaroni penguins, leading to the decline in their population. We used: (1) satellite-tracking data to investigate the spatial separation of the Bird Island populations of these two species whilst at sea during the breeding seasons of 1999 and 2000 and (2) diet data to assess potential changes in their trophic niches between 1989 and 2000. Foraging ranges of the two species showed considerable overlap in both years, but the concentrations of foraging activity were significantly segregated spatially. The size of krill taken by both species was very similar, but over the last 12 years the prevalence of krill in their diets has diverged, with nowadays less krill in the diet of macaroni penguins than in that of Antarctic fur seals. Despite a significant degree of segregation in spatial resource use by the study populations, it is likely that the South Georgia populations of Antarctic fur seal and macaroni penguin exploit the same krill population during their breeding season. For explaining the opposing population trends of the two species, the relative contributions of independent differential response to interannual variation in krill availability and of interspecies competition cannot be resolved with available evidence. The likely competitive advantage of Antarctic fur seals will be enhanced as their population continues to increase, particularly in years of krill scarcity.     

Intertidal distribution,population dynamics and production of the amphipod Uhlorchestia spartinophila in a Georgia,USA, salt marsh

The talitrid amphipod Uhlorchestia spartinophila Bousfield and Heard occurs in close association with the smooth cordgrass Spartina alterniflora Loisel in salt marshes along the U.S. Atlantic coast. In order to assess its potential as a prey resource for secondary consumers, we followed the population and production dynamics of this amphipod from 3 November 1990 to 2 October 1991 in a salt marsh on Sapelo Island, Georgia. Semimonthly samples were taken along an intertidal transect, which extended from a vegetated creekbank levee landward 140 m to a site near the upland edge of the marsh. Amphipod densities ranged from 9 to 826 indm^-2 and were greatest in the levee and high marsh habitats at opposite ends of the transect. The highest densities occurred in March to May and the lowest in November and December. Specific growth rates, which ranged from 0.001 to 0.024 mm mm^-1 d^-1 length and 0.003 to 0.068 mg mg^-1 d^-1 AFDW (ash-free dry weight), were least in winter and decreased with increasing amphipod size. Although some reproduction occurred year-round, most of the population's reproductive output was from January to May, when adults had the greatest size-specific mass. Sex ratio usually favored females, which were larger than males. Minimum adult female size was 5.4 mm total length (TL). Broods included from 1 to 28 eggs or young and increased with increasing body size, averaging 7.4 young for an average-size female of 7.6 mm TL. Annual production, which ranged from 0.769 to 1.444 g AFDW m^-2, was least in the low marsh and greatest in the levee habitat. Production:biomass ratios were 15.4 to 17.3 in different habitats. Such high turnover rates, together with the population's broad intertidal distribution, suggest a greater contribution to trophic dynamics than is implied by the relatively low standing stock biomass of U. spartinophila in this marsh system.     

The ecology of two sandy beaches in south west India. III. Observations on the population of Donax incarnatus and D. spiculum

The biology of two species of Donax, D. incarnatus Gmelin and D. spiculum Reeve on two beaches in south west India is described. Two year groups of D. incarnatus were present on both beaches, from settlements during the monsoon period in 1967 and 1968. At Shertallai, both groups were studied through the year, and data on growth, mortality and production are presented. At Cochin, the rate of growth was slower and the maximum size attained smaller, but mortality during the early monsoon precluded study of D. incarnatus through a full year. D. spiculum occurred at Cochin mainly during the pre-monsoon period, and at Shertallai during the post-monsoon. The species has a shorter life-span than D. incarnatus, but its irregular occurrence did not allow detailed production estimates.     

Repeated geographic divergence in behavior: a case study employing phenotypic trajectory analyses

Environmental effects on behavior have long been a focus of behavioral ecologists. Among the important drivers of behavior is predation environment, which can include the presence/absence of predators, differences in resource availability, and variation in individual density. Environments with predators are often more ecologically complex and “risky” than those without predators. Populations from these environments are sometimes more active and explorative than populations from low-risk, less complex environments. To date, most comparative studies of behavior are limited to within-species comparisons of populations from divergent environments, but neglect comparisons between species following speciation, thus limiting our understanding of post-speciation behavioral evolution. Brachyrhaphis fishes provide an ideal system for studying correlations between divergent environments and behavior within and between species. Here, we test for differences in two behavioral traits—activity and exploration —between sister species Brachyrhaphis roseni and Brachyrhaphis terrabensis that occur in divergent predation environments. Species differed in activity and exploration, with higher activity and exploration levels in populations that co-occur with predators. Furthermore, we found drainage-by-species interactions, indicating that the nature of divergence varied geographically. Using the recently developed phenotypic trajectory analysis (PTA), we quantified this difference and found that, while the geographically isolated populations of sister species tended to evolve in parallel, the magnitude of divergence between species differed between drainages. Our results highlight the utility of PTA for multivariate behavioral data and corroborate past predictions that complex and risky environments are correlated with increased activity and exploration levels and that divergence continues post-speciation.     

Chernobyl as a population sink for barn swallows: tracking dispersal using stable-isotope profiles.

Stable-isotope profiles of feathers can reveal the location or habitat used by individual birds during the molting period. Heterogeneity in isotope profiles will reflect heterogeneity in molt locations, but also heterogeneity in breeding locations, because spatial heterogeneity in molt locations will be congruent with spatial heterogeneity in breeding locations in species with high connectivity between breeding and molting sites. We used information on the congruence of spatial heterogeneity in molt and breeding location to study population processes in Barn Swallows (Hirundo rustica) from a region. near Chernobyl, Ukraine, that has been radioactively contaminated since 1986; from an uncontaminated control region near Kanev, Ukraine; and from a sample of pre-1986 museum specimens used to investigate patterns prior to the nuclear disaster at Chernobyl, from both regions. Previous studies have revealed severe reductions in Barn Swallow reproductive performance and adult survival in the Chernobyl region, implying that the population is a sink and unable to sustain itself. Female Barn Swallows are known to disperse farther from their natal site than males, implying that female stable-isotope profiles should tend to be more variable than profiles of males. However, if the Barn Swallows breeding at Chernobyl are not self-sustaining, we would expect males there also to originate from a larger area than males from the control region. We found evidence that the sample of adult Barn Swallows from the Chernobyl region was more isotopically heterogeneous than the control sample, as evidenced from a significant correlation between feather sigma13C and sigma15N values in the control region, but not in the Chernobyl region. Furthermore, we found a significant difference in feather sigma15N values between regions and periods (before and after 1986). When we compared the variances in sigma13C values of feathers, we found that variances in both sexes from post-1986 samples from Chernobyl were significantly larger than variances for feather samples from the control region, and than variances for historical samples from both regions. These findings suggest that stable-isotope measurements can provide information about population processes following environmental perturbations.     

Wet deposition chemistry studies at Suva, Fiji, a remote tropical island site in the south Pacific

A field project encompassing wet-only rainwater sampling was initiated as a bilateral Fiji/Australia activity. Normally, biweekly samples were collected, using a wet-only rainwater sampler, and analysed for H⁺, Na⁺, K⁺, Mg²⁺, NH₄ ⁺, Cl^–, NO₃ ^–, SO₄ ^2–, PO₄ ^3-, methane sulphonic acid, oxalic acid, formic acid and acetic acid. The pH of the rainwater ranged between 5.730 and 4.480 with an average value of 5.176, slightly lower than the pH of unpolluted rainwater saturated with atmospheric CO₂(pH = 5.650). Na⁺and Cl^–were the major ions with average concentrations of 98.15 M and 109.57 M respectively. There is an excellent correlation between the cation sum (average 147.71 eq L^-1) and the anion sum (average 142.12 eq L^-1) attesting to the quality of the data generated. This paper presents the detailed results of the study for a relatively clean remote island site in Suva, Fiji, latitude 18° 09 S, longitude 178° 27 E, height 6 m, and outlines prospects for further work.     

Graph theory as a proxy for spatially explicit population models in conservation planning.

Spatially explicit population models (SEPMs) are often considered the best way to predict and manage species distributions in spatially heterogeneous landscapes. However, they are computationally intensive and require extensive knowledge of species' biology and behavior, limiting their application in many cases. An alternative to SEPMs is graph theory, which has minimal data requirements and efficient algorithms. Although only recently introduced to landscape ecology, graph theory is well suited to ecological applications concerned with connectivity or movement. This paper compares the performance of graph theory to a SEPM in selecting important habitat patches for Wood Thrush (Hylocichla mustelina) conservation. We use both models to identify habitat patches that act as population sources and persistent patches and also use graph theory to identify patches that act as stepping stones for dispersal. Correlations of patch rankings were very high between the two models. In addition, graph theory offers the ability to identify patches that are very important to habitat connectivity and thus long-term population persistence across the landscape. We show that graph theory makes very similar predictions in most cases and in other cases offers insight not available from the SEPM, and we conclude that graph theory is a suitable and possibly preferable alternative to SEPMs for species conservation in heterogeneous landscapes.     

Integral projection models for finite populations in a stochastic environment

Continuous types of population structure occur when continuous variables such as body size or habitat quality affect the vital parameters of individuals. These structures can give rise to complex population dynamics and interact with environmental conditions. Here we present a model for continuously structured populations with finite size, including both demographic and environmental stochasticity in the dynamics. Using recent methods developed for discrete age-structured models we derive the demographic and environmental variance of the population growth as functions of a continuous state variable. These two parameters, together with the expected population growth rate, are used to define a one-dimensional diffusion approximation of the population dynamics. Thus, a substantial reduction in complexity is achieved as the dynamics of the complex structured model can be described by only three population parameters. We provide methods for numerical calculation of the model parameters and demonstrate the accuracy of the diffusion approximation by computer simulation of specific examples. The general modeling framework makes it possible to analyze and predict future dynamics and extinction risk of populations with various types of structure, and to explore consequences of changes in demography caused by, e.g., climate change or different management decisions. Our results are especially relevant for small populations that are often of conservation concern.     

Temporal patterns of populations in a warming world: a modelling framework

In this paper, we present an approach for describing the environmentally induced temporal pattern of structured populations by partial integro-differential equations. Populations are structured according to size or stage. Growth, energy allocation and stage transitions are affected by environmental conditions of which temperature, photoperiod, water depth and food supply were taken into account. The resulting modelling framework was applied to describe, analyse and predict alterations in populations with continuous development, populations with distinct state structures and interacting populations. Our exemplary applications consider populations of freshwater Amphipoda, Isopoda and Odonata. The model was capable of simulating life cycle alterations in dependence on temperature in interaction with other environmental factors: (1) population dynamics, (2) seasonal regulation, (3) water depth-dependent dispersal, (4) intraguild predation and (5) consumer-resource dynamics.     

Primary sex ratios in zebra finches: no evidence for adaptive manipulation in wild and semi-domesticated populations.

When breeding diet is restricted, domesticated zebra finches,Taeniopygia guttata, produce male-biased primary and secondary sex ratios, but unexpectedly produce unbiased ratios when food is unrestricted. We investigated the primary sex ratios (at laying) of wild zebra finches in southeastern Australia in response to food supplementation and environmental factors predicted to enhance female breeding condition and to bias the primary sex ratio towards daughters. Molecular sexing of all nestlings in 54 complete broods where every egg hatched, failed to show any significant biases from random. Time of egg laying (month, season) and environmental conditions (rainfall, temperature) did not significantly predict variation in the primary sex ratio, but time of breeding did affect clutch size. Wild zebra finches at our colony did not bias their sex allocation as there were no differences in the primary sex ratio and no differences in the numbers and mass of sons and daughters at the end of parental care (day 35–40 post-hatch). Biases in primary sex ratio of our wild population are probably weak or non-existent possibly due to the unpredictable environment and/or multiple contrary selective forces acting on sex ratios. We also investigated the effects of photoperiod, biases in the adult sex ratio, and parental attractiveness on primary sex ratios of semi-domesticated, laboratory zebra finches. Molecular sexing of three-day old embryos from complete clutches, failed to reveal significant biases from random. In contrast to previous studies, sex of eggs did not correlate with laying order and egg mass declined with order, rather than increased. Domestication may be responsible for these differences.     

Environmental and social determinants of anuran lekking behavior: intraspecific variation in populations at thermal extremes

Environmental and social factors are critical to determine the timing and duration of lekking behavior since they provide species with signs to maximize benefits over costs in sexual displays. However, these factors have rarely been studied under different environmental conditions, and thus, it remains unclear whether exogenous factors affecting group displays show a general species-specific pattern or whether they are population-specific. Using audio-trapping techniques, we compared factors influencing the daily occurrence and duration of lekking behavior in two populations of Hyla molleri and two populations of Hyla meridionalis located at the thermal extremes (coldest vs. hottest) of their Iberian distribution range. From 12,240 hourly recordings over one season, multimodel inference revealed that the major determinants of chorus occurrence were similar between populations and species (i.e., chorus size the previous day, daytime air temperature, relative humidity, and barometric pressure), and accounted for 51–79 % of its deviance. In contrast, the major determinants of chorus duration differed between populations and species (i.e., chorus size, number of day, and air temperature and relative humidity at the onset of the chorus), and accounted for 38–69 % of its variance. Our findings suggest that the decision making related to lek attendance is environment-dependent, takes place at time between lekking events, and is associated with exogenous factors that may be both stable across species ranges and population-specific when populations are under different climatic conditions. This intraspecific variation might be underlain by plasticity mechanisms providing tree frogs with means to cope with changing environments. Moreover, social facilitation related to male-male acoustic competition seems to play a relevant role on the daily time invested by males in lek attendance.     

Copper tolerance in a population of Silene vulgaris ssp. maritima (A. & D. Love) at Dolfrwynog Bog near Dolgellau,North Wales

Clones of Silene vulgaris ssp. maritima individuals from Dolfrwynog Bog, North Wales and from a coastal control site were propagated under standardised environmental conditions. After five months, cuttings were taken and tested for copper tolerance by means of root extension analysis in solutions of various different copper concentrations. Indices of tolerance suggested that individuals from the Dolfrwynog population were more resistant to elevated copper concentrations than were the control population individuals. Due to the initial five months under standardised conditions, it was assumed that the cloned plant material would have lost all plastic adaptive responses to its native environment. If this assumption was valid then the differences in copper tolerance observed between the two populations had a genetic basis and the Dolfrwynog Bog population is a copper tolerant ecotype.