Population Biology

Estimating colony and breeding population size for nocturnal burrow-nesting seabirds.

by Alex Chubaty

Heather L. Major & Alex M. Chubaty (2009) Marine Ecology Progress Series 454:83-90

Estimating colony areas, locations, population sizes, and trends, are all important aspects of managing animal... more Estimating colony areas, locations, population sizes, and trends, are all important aspects of managing animal populations. The ability to assess population trends and delineate important wildlife areas remains a top priority for managers and conservation biologists. Yet, outdated labourious estimation methods remain in high use. By simulating known populations on known island sizes and using established transect and quadrat survey methods we asked whether using inverse distance weighting (IDW) interpolations in ArcGIS improved estimates of colony area and population size for nocturnal burrow-nesting seabirds over conventional global interpolation methods. We performed 100 simulations for each of three population sizes (500, 1000, and 50 000 breeding pairs) on three island sizes (10 ha, 50 ha, and 500 ha), excluding the largest population size on the smallest island size, for a total of 800 simulated islands. We estimated colony area and population size for each simulated island using both IDW interpolations and an established global interpolation method. Accuracy of each estimate was then calculated and using an information theoretic approach we found that IDW interpolation estimates were overall more accurate when estimating population size but we found no difference in colony area accuracy between interpolation methods. We recommend using IDW interpolations to estimate colony area and population size along with consistency in survey structure both among study sites and years. We also recommend maintaining a consistent transect length whenever possible to ensure observer bias does not influence areas surveyed.

VARIATION AMONG INDIVIDUALS IN CONE PRODUCTION IN PINUS PALUSTRIS (PINACEAE)

by Gordon Fox

American Journal of Botany 99: 1-6

• Premise of the study: Reproductive output varies considerably among individuals within plant populations, and this... more • Premise of the study: Reproductive output varies considerably among individuals within plant populations, and this is especially
so in cone production of conifers. While this variation can have substantial effects on populations, little is known about
its magnitude or causes.
• Methods: We studied variation in cone production for 2 years within a population of Pinus palustris Mill. (longleaf pine;
Pinaceae). Using hurdle models, we evaluated the importance of burn treatments, tree size (dbh), canopy status (open, dominant,
subordinate), and number of conspecifi c neighbors within 4 m (N 4 ).
• Key results: Cone production of individuals — even after accounting for other variables — was strongly correlated between
years. Trees in plots burned every 1, 2, or 5 years produced more cones than those burned every 7 years, or unburned. Larger
trees tend to produce more cones, but the large effects of the other factors studied caused substantial scatter in the dbh-cone
number relationship. Among trees in the open, dbh had little explanatory power. Subordinate trees with three neighbors produced
no cones.
• Conclusions: Tree size alone was a weak predictor of cone production. Interactions with neighbors play an important role in
generating reproductive heterogeneity, and must be accounted for when relating cone production to size. The strong betweenyear
correlation, together with the large variance in cone production among trees without neighbors, suggests that still more of
the variance may be explainable, but requires factors outside of our study.

Annual cycle of activity, reproduction, and body mass of Anatolian ground squirrels (Spermophilus xanthoprymnus) in Turkey

by Hakan Gur

RESEARCH ARTICLE. GÜR H. and KART GÜR M. 2005. Annual cycle of activity, reproduction, and body mass of Anatolian ground squirrels (Spermophilus xanthoprymnus) in Turkey. JOURNAL OF MAMMALOGY. 86: 7-14. With cover photograph.

Over a 3-year period (1999–2001), we monitored the annual timing of reproduction and hibernation and accompanying... more Over a 3-year period (1999–2001), we monitored the annual timing of reproduction and hibernation and accompanying changes in body mass of free-living Anatolian ground squirrels (Spermophilus xanthoprymnus) in steppe habitat about 50 km south of Ankara, Turkey. Adult males emerged from hibernation during March, before breeding females. Yearling males emerged with adult males in 2000 but not in 2001. Yearlings of both sexes and adult females were at their lowest body mass of the active season at emergence. Adult males were 139–205% heavier than other age and sex classes when they emerged. Their body mass was near the lowest of the active season at the end of mating season. All adult males had descended testes at emergence, and most yearling males were reproductively active after their 1st hibernation. Females mated shortly after their emergence from hibernation and weaned only 1 litter each year. Females 1st reproduced as yearlings. Parturition occurred in April, and juveniles appeared aboveground from mid- to late May. Thereafter, all age and sex classes were simultaneously active until immergence. In each year, juveniles immerged into hibernation after nonjuveniles. Thus, the annual cycle of Anatolian ground squirrels resembles generally those of most species of hibernating ground squirrels in Europe and North America.

Keywords: Anatolian ground squirrels; Ankara; annual cycle; body mass; reproduction; Rodentia; Sciuridae; Spermophilus xanthoprymnus

Sex ratio of a population of Anatolian ground squirrels Spermophilus xanthoprymnus in Central Anatolia, Turkey

by Hakan Gur

RESEARCH ARTICLE. GÜR H. and BARLAS N. 2006. Sex ratio of a population of Anatolian ground squirrels Spermophilus xanthoprymnus in Central Anatolia, Turkey. ACTA THERIOLOGICA. 51: 61-67.

We studied the sex ratio of a population of Anatolian ground squirrels, Spermophilus xanthoprymnus (Bennett, 1835),... more We studied the sex ratio of a population of Anatolian ground squirrels, Spermophilus xanthoprymnus (Bennett, 1835), living in a steppe area about 50 km south of Ankara, Central Anatolia, Turkey in 1999–2001. The sex ratio among juveniles and yearlings did not differ from 1:1, but the sex ratio among adults (³ 2 years old) was biased toward females. We concluded that from their second summer of life as yearlings onwards, males experienced higher mortality than did females. Such higher mortality is common in ground squirrels, and is likely due to the risks encountered when males disperse from their natal areas.

Keywords: Life span; population demography; predation; sex ratio; Spermophilus; survival

A global population redistribution in a migrant shorebird detected with continent‐wide qualitative breeding survey data

by Yvonne Verkuil

Diversity and Distributions 17, 144–151, 2011

Aim: Over the last two decades, thousands of northward migrating ruffs (Philomachus pugnax) have disappeared from... more Aim: Over the last two decades, thousands of northward migrating ruffs (Philomachus pugnax) have disappeared from western European staging sites. These migratory ruffs were partly temperate breeding birds, but most individuals head towards the Eurasian Arctic tundras where 95% of the global population breeds. This regional decline may represent either: (1) local loss of breeding birds in western Europe, (2) a global decline, (3) shift(s) in distribution or (4) a combination of these.

Location: Northern Eurasia.

Methods: To put the declines in western Europe in context, we analysed Arctic monitoring data from the last two decades (Soloviev & Tomkovich, 2009) to detect changes in regional breeding densities across northern Eurasia. We used a novel approach applying generalized additive modelling (GAM) and generalized estimations equations (GEE).

Results: We show that the global breeding population of ruffs has made a significant eastwards shift into the Asian part of the breeding range. In the European Arctic, ruffs decreased during the last 18 years. At the same time, in western Siberia, ruffs increased. In eastern Siberia, no significant population changes could be detected. These changes corroborate the finding that during northward migration, growing numbers of ruffs avoided staging areas in the Netherlands and Sweden and started migrating along a more easterly route leading into western Siberia.

Main conclusions: We detected an unprecedented large-scale population redistribution of ruffs and suggest that this is a response to loss of habitat quality at the traditional staging site in the Netherlands.

Role of recent and old riverine barriers in fine-scale population genetic structure of Geoffroy's tamarin (Saguinus geoffroyi) in the Panama Canal watershed

by Sam Diaz-Munoz

Ecology and Evolution (Early View 2011)

The role of physical barriers in promoting population divergence and genetic structuring is well known. While it is... more The role of physical barriers in promoting population divergence and genetic structuring is well known. While it is well established that animals can show genetic structuring at small spatial scales, less well-resolved is how the timing of the appearance of barriers affects population structure. This study uses the Panama Canal watershed as a test of the effects of old and recent riverine barriers in creating population structure in Saguinus geoffroyi, a small cooperatively breeding Neotropical primate. Mitochondrial sequences and microsatellite genotypes from three sampling localities revealed genetic structure across the Chagres River and the Panama Canal, suggesting that both waterways act as barriers to gene flow. F-statistics and exact tests of population differentiation suggest population structure on either side of both riverine barriers. Genetic differentiation across the Canal, however, was less than observed across the Chagres. Accordingly, Bayesian clustering algorithms detected between two and three populations, with localities across the older Chagres River always assigned as distinct populations. While conclusions represent a preliminary assessment of genetic structure of S. geoffroyi, this study adds to the evidence indicating that riverine barriers create genetic structure across a wide variety of taxa in the Panama Canal watershed and highlights the potential of this study area for discerning modern from historical influences on observed patterns of population genetic structure.

Kendall, B. E., G. A. Fox, M. Fujiwara, and T. Nogeire. 2011. Demographic heterogeneity, cohort selection and population growth.

by Gordon Fox

Ecology 92:1985-1993.

Demographic heterogeneity—variation among individuals in survival and reproduction—is ubiquitous in natural... more Demographic heterogeneity—variation among individuals in survival and reproduction—is ubiquitous in natural populations. Structured population models address heterogeneity due to age, size, or major developmental stages. However, other important
sources of demographic heterogeneity, such as genetic variation, spatial heterogeneity in the environment, maternal effects, and differential exposure to stressors, are often not easily measured and hence are modeled as stochasticity. Recent research has elucidated the role of demographic heterogeneity in changing the magnitude of demographic stochasticity in small populations. Here we demonstrate a previously unrecognized effect: heterogeneous survival in long-lived species can increase the long-term growth rate in populations of any size. We illustrate this result using simple models in which each individual’s annual survival rate is independent of age but survival may differ among individuals within a cohort. Similar models, but with nonoverlapping generations, have been extensively studied by demographers, who showed that, because the more ‘‘frail’ individuals are more likely to die at a young age, the average survival rate of the cohort increases with age. Within ecology and evolution, this phenomenon of ‘‘cohort selection’’ is increasingly appreciated as a confounding factor in studies of senescence. We show that, when placed in a population model with overlapping generations, this heterogeneity also causes the asymptotic population growth rate k to increase, relative to a homogeneous population with the same mean survival rate at birth. The increase occurs because, even integrating over all the cohorts in the population, the population becomes increasingly dominated by the more robust individuals. The growth rate increases monotonically with the variance in survival rates, and the effect can be substantial, easily doubling the growth rate of slow-growing populations. Correlations between parent and
offspring phenotype change the magnitude of the increase in k, but the increase occurs even for negative parent–offspring correlations. The effect of heterogeneity in reproductive rate on
k is quite different: growth rate increases with reproductive heterogeneity for positive parent–offspring correlation but decreases for negative parent–offspring correlation. These effects of demographic heterogeneity on k have important implications for population dynamics, population viability analysis, and evolution.

Variation among individuals and reduced demographic stochasticity

by Gordon Fox

Demographic stochasticity and the variance reduction effect

by Gordon Fox

Spatial structure, environmental heterogeneity, and population dynamics: analysis of the coupled logistic map

by Gordon Fox

Extinction risk of heterogeneous populations

by Gordon Fox

Consequences of heterogeneity in survival probability in a population of Florida scrub‐jays

by Gordon Fox

Variation in recruitment and early demography in Pinus rigida following crown fire in the pine barrens of Long Island, New York

by Gordon Fox

Sources of variation in growth, form, and survival in dwarf and normal-stature pitch pines (Pinus rigida, Pinaceae) in long-term transplant experiments

by Gordon Fox

Modeling density dependence and climatic disturbances in caribou: a case study from the Bathurst Island complex, Canadian High Arctic

by Mike Ferguson

Tews J, Ferguson MAD, Fahrig L. 2007. Modeling density dependence and climatic disturbances in caribou: A case study from the Bathurst Island complex, Canadian high arctic. Journal of Zoology 272(2): 209-217.

Keywords: climate change; density independence; environmental stochasticity; Peary caribou; population dynamics; population viability analysis; simulation model

Peary caribou Rangifer tarandus pearyi is the northernmost subspecies of Rangifer in North America and endemic to the... more Peary caribou Rangifer tarandus pearyi is the northernmost subspecies of Rangifer in North America and endemic to the Canadian High Arctic. Because of severe population declines following years of unfavorable winter weather with ice coating on the ground or thicker snow cover, it is believed that density-independent disturbance events are the primary driver for Peary caribou population dynamics. However, it is unclear to what extent density dependence may affect population dynamics of this species. Here, we test for different levels of density dependence in a stochastic, single-stage population model, based on available empirical information for the Bathurst Island complex (BIC) population in the Canadian High Arctic. We compare predicted densities with observed densities during 1961–2001 under various assumptions of the strength of density dependence. On the basis of our model, we found that scenarios with no or very low density dependence led to population densities far above observed densities. For average observed disturbance regimes, a carrying capacity of 0.1 caribou km−2 generated an average caribou density similar to that estimated for the BIC population over the past four decades. With our model we also tested the potential effects of climate change-related increases in the probability and severity of disturbance years, that is unusually poor winter conditions. On the basis of our simulation results, we found that, in particular, potential increases in disturbance severity (as opposed to disturbance frequency) may pose a considerable threat to the persistence of this species.

Sex structure of populations of Glechoma hederacea L. (Lamiaceae) in Izhevsk

by Denis Melnikov

Экологический сборник 3. Труды молодых ученых Поволжья, Тольятти

The analysis of the structure of sexual forms in the population Glechoma hederacea city of Izhevsk. (article in Russian) The analysis of the structure of sexual forms in the population Glechoma hederacea city of Izhevsk. (article in Russian)

Local Mobile Gene Pools Rapidly Cross Species Boundaries To Create Endemicity within Global Vibrio cholerae Populations.

by Otto X. Cordero Sanchez

Yan Boucher*, Otto X. Cordero, Alison Takemura, Dana E. Hunt, Klaus Schliep, Eric Bapteste, Philippe Lopez, Cheryl L. Tarrd, and Martin F. Polz
(2011) Mbio.

Vibrio cholerae represents both an environmental pathogen and a widely distributed microbial species comprised of... more Vibrio cholerae represents both an environmental pathogen and a widely distributed microbial species comprised of closely related strains occurring in the tropical to temperate coastal ocean across the globe (Colwell RR, Science 274:2025-2031, 1996; Griffith DC, Kelly-Hope LA, Miller MA, Am. J. Trop. Med. Hyg. 75:973-977, 2006; Reidl J, Klose KE, FEMS Microbiol. Rev. 26:125-139, 2002). However, although this implies dispersal and growth across diverse environmental conditions, how locally successful populations assemble from a possibly global gene pool, relatively unhindered by geographic boundaries, remains poorly understood. Here, we show that environmental Vibrio cholerae possesses two, largely distinct gene pools: one is vertically inherited and globally well mixed, and the other is local and rapidly transferred across species boundaries to generate an endemic population structure. While phylogeographic analysis of isolates collected from Bangladesh and the U.S. east coast suggested strong panmixis for protein-coding genes, there was geographic structure in integrons, which are the only genomic islands present in all strains of V. cholerae (Chun J, et al., Proc. Natl. Acad. Sci. U. S. A. 106:15442-15447, 2009) and are capable of acquiring and expressing mobile gene cassettes. Geographic differentiation in integrons arises from high gene turnover, with acquisition from a locally cooccurring sister species being up to twice as likely as exchange with conspecific but geographically distant V. cholerae populations. IMPORTANCE Functional predictions of integron genes show the predominance of secondary metabolism and cell surface modification, which is consistent with a role in competition and predation defense. We suggest that the integron gene pool's distinctness and tempo of sharing are adaptive in allowing rapid conversion of genomes to reflect local ecological constraints. Because the integron is frequently the main element differentiating clinical strains (Chun J, et al., Proc. Natl. Acad. Sci. U. S. A. 106:15442-15447, 2009) and its recombinogenic activity is directly stimulated by environmental stresses (Guerin E, et al., Science 324:1034, 2009), these observations are relevant for local emergence and subsequent dispersal.

A Discrete Event System Specification (DEVS)-Based Model of Consanguinity

by Muaz Niazi

Citation:

Noreen Akhtar, Muaz Niazi, Amir Hussain & Farah Mustafa (2011), A Discrete Event System Specification (DEVS)-Based Model of Consanguinity, Elsevier Journal of Theoretical Biology 285(1), 103-112, doi:10.1016/j.jtbi.2011.05.038.

http://dx.doi.org/10.1016/j.jtbi.2011.05.038

Consanguinity or inter-cousin marriage is a phenomenon quite prevalent in certain regions around the globe.... more Consanguinity or inter-cousin marriage is a phenomenon quite prevalent in certain regions around the globe. Consanguineous parents have a higher risk of having offspring with congenital disorders. It is difficult to model large scale consanguineous parental populations because of disparate cultural issues unique to regions and cultures across the globe. Although consanguinity has previously been studied as a social problem, it has not been
modeled from a biological perspective. Discrete Event System Specification (DEVS) is a powerful modeling formalism for the study of intricate details of real-world complex systems. In this paper, we have developed a DEVS model to get an insight into the role of consanguineous marriages in the evolution of congenital disorders in a population. As proof-of-concept, we further developed a consanguinity simulation model in Simio simulation software. Simulation results validated using population growth data show the effectiveness of this approach in the modeling of consanguinity in populations.

Status and trends of Rangifer tarandus and Ovibos moschatus populations in Canada

by Mike Ferguson

We identified 97 Rangifer tarandus and 17 Ovibos moschatus populations in Canada. In July 1991, the Canadian... more We identified 97 Rangifer tarandus and 17 Ovibos moschatus populations in Canada. In July 1991, the Canadian populations totalled 1.9 to 2.6 million caribou, 13 600 reindeer and 108 600 muskoxen. Seven barren-ground caribou populations contributed about 75% to Canada's total number of caribou. Most population trends of these barren-ground caribou had shiftet from increasing in the early 1980s to stable or decreasing in the late 1980s. The George River herd of Quebec and Labrador has been decreasing since 1987, but remains the largest Canadian caribou population. The ecological factors driving barren-ground caribou population dynamics are not well understood. Arctic islands caribou are about 17% of all Canadian caribou. Over 60% of Arctic islands caribou occurred on Baffin Island. Most Arctic islands populations were decreasing with the exceptions of Southampton, Bathurst, Victoria and Baffin islands. Movements within and between islands are not well understood, and probably limit the usefulness of small surveys for indicating long-term trends of Arctic islands caribou populations. Woodland caribou form about 7% of all Canadian caribou, with about 40% of these occurring on the island of Newfoundland. Most Canadian woodland caribou have not been well studied or censused. In many areas, they were faced with an increasing rate of habitat loss. Exceptions included: some eastern Yukon populations and most Newfoundland populations which were increasing. Over 70% of the Canadian muskox population occurred on Banks and Victoria islands. Almost all muskox populations were increasing, especially those on Banks, Victoria, Melville and Bathurst islands. Muskoxen on the mainland Northwest Territories are re-colonizing southern portions of their historical distribution.

Mass emigration of Arctic tundra caribou from a traditional winter range: population dynamics and physical condition

by Mike Ferguson

Ferguson and Messier. 2000. Mass Emigration of Arctic Tundra Caribou from a Traditional Winter Range: Population Dynamics and Physical Condition. Journal of Wildlife Management 64: 168-178

Keywords: Baffin Island, Canada, caribou, cumulative density-dependent effects, fecundity, habitat fidelity, Northwest Territories, Nunavut, plant-herbivore interactions, range shift, Rangifer tarandus, winter forage depletion

Major declines of populations of caribou and reindeer (Rangifer tarandus) that permanently reside on Arctic tundra... more Major declines of populations of caribou and reindeer (Rangifer tarandus) that permanently reside on Arctic tundra have been attributed to short-term inaccessibility of forage through restrictive snow cover. Such density-independent phenomena would produce unpredictable changes in populations of Arctic tundra caribou. In 1985, Inuit correctly predicted mass emigration from the winter range of a caribou subpopulation on Foxe Peninsula (FP), southern Baffin Island, Canada. During 1982-94, we conducted aerial surveys, satellite telemetry, and physical condition studies to examine features of the predicted range shift. Between 1984 and 1992, caribou density on upland terrain on FP dropped (P < 0.001) from 6.2 to 0.3 caribou/km2. Cows began to emigrate en masse during winter 1988-89 (P = 0.10) toward Meta Incognita Peninsula (MIP), where caribou showed greater fidelity to that wintering area during 1988-94 (P = 0.005). Density of caribou on upland terrain on MIP increased (P = 0.001) from 0.2 to 5.0 caribou/km2 between 1982 and 1992. In April 1992, body size did not differ (P - 0.47) between FP and MIP. Cows on MIP had greater (P - 0.04) fat and muscle reserves than cows on FP, while only fat reserves of MIP bulls were greater than (P - 0.03) those of FP bulls. Our results support Inuit observations of declining physical condition of FP caribou in the early 1980's, and their view that the range shift was caused by cumulative annual overgrazing of the winter range during the previous 10 to 30 yr. Fewer cows on FP were pregnant (2 of 8) than on MIP (10 of 10; P = 0.002). Calf:cow ratios were higher (P = 0.05) on MIP than on FP in 1992. Although few caribou had occupied MIP for 50 yr before 1988-89, MIP caribou were in relatively poor condition by April 1992 compared to those on overgrazed Coats Island during mild winters. Winter range shifts and population declines by Arctic tundra caribou may be predictable. Ecological indicators may enable managers to mitigate the effects of overgrazing on caribou populations through intensive harvesting at critical stages during long-term population increases.