Spatial Variation In Population Dynamics Research Articles

Spatio-temporal metapopulation trends: The coconut crabs of Zanzibar.

Species experience a variety of environmental and anthropogenic conditions across their ranges leading to spatial variation in population dynamics. Understanding population dynamics under different conditions is important but it is challenging to allocate limited effort to spatial and temporal subpopulation monitoring. Using GLMMs, we analyze survey data of a metapopulation of coconut crabs spanning 7 years and 15 sites in and near the Pemba archipelago, Zanzibar, to estimate trends in population size (based on catch per unit effort), weight and sex ratio at the meta- and subpopulation level and investigate anthropogenic drivers of these trends. We found that the overall metapopulation has remained stable in terms of size and composition over the survey period, but observed diverging trends in population size and sex ratio at some subpopulations. Formal protection of sites was associated with positive population trends. Of nine sites for which we could estimate site-specific trends, three showed increasing and two decreasing trends, whereas four sites had stable subpopulations. Although anthropogenic factors affected the average weight, and the incidence of small and large individuals, we found no temporal trends in any weight-related measures. Furthermore, there were no apparent patterns between weight-related measures and subpopulation trends. The metapopulation was biased toward males, and exploitation appeared to be associated with declining trends in the proportion of females, likely an artifact of a strong decline in the proportion of females in one of only two exploited sites in the dataset. Educational campaigns implemented in 2020 at six sites were not related to higher population sizes in later surveys. The variable trends in subpopulation sizes and composition highlight the need for spatially replicated monitoring in metapopulations. The analyses further provide a detailed baseline for future subpopulation studies of this vulnerable species in one of its last remaining metapopulations in the Western Indian Ocean.

Life History Traits of the Stygophilous Amphipod Synurella ambulans in the Hyporheic Zone of the Lower Reaches of the Upper Sava River (Croatia)

Estimating the growth and population dynamics of crustaceans is important for understanding the role of species in ecosystems and for conservation and monitoring purposes. This study investigated temporal and spatial variation in population dynamics (growth rate, instantaneous mortality rates, and longevity) of the stygophilous freshwater amphipod Synurella ambulans (F. Müller, 1846), and influencing environmental factors. Seasonal sampling was conducted from December 2018 to October 2019 at two sampling sites (Jarun and Medsave) along the Sava River in northwestern Croatia. A Bhattacharya cohort analysis was applied to the length-frequency data using the FISAT software package. At least four cohorts were distinguished during the year. The possible influence of environmental factors on growth parameters was investigated using Canonical Correspondence Analysis (CCA), which revealed that the important environmental factors influencing S. ambulans abundance were water temperature and dissolved oxygen concentration. The average total body length (TBL) of females was 4.25 mm, while the TBL of males was 3.34 mm. The asymptotic length (L∞) and growth coefficient (K) were estimated to be 6.30 mm and 0.92 year−1 for females and 5.40 mm and 0.59 year−1 for males, respectively, at the Jarun site. L∞ and K were estimated to be 7.20 mm and 0.34 year−1, respectively, for females and 4.00 mm and 1.20 year−1, respectively, for males at the Medsave site. Estimated total mortality (Z) for each sex had higher values for males than females at both sampling sites. The lack of ecological knowledge on S. ambulans populations and relationships with invertebrate communities in the hyporheic zone of the large river ecosystems emphasises the importance of a detailed study for protecting this species and its vulnerable ecotonal groundwater-connected environment.

Drivers of large‐scale spatial demographic variation in a perennial plant

AbstractTo understand how the environment drives spatial variation in population dynamics, we need to assess the effects of a large number of potential drivers on vital rates (survival, growth, and reproduction) and explore these relationships over large geographical areas and broad environmental gradients. In this study, we examined the effects of a wide variety of abiotic and biotic environmental factors on the demography of the forest understory herb Actaea spicata between 2017 and 2019 at 40 sites across Sweden, including the northern range margin of its distribution. We assessed the effects of potential environmental drivers on vital rates using generalized linear mixed models (GLMMs) and then quantified the impact of each important driver on population growth rate (λ) using integral projection models (IPMs). Population dynamics of A. spicata were mostly driven by environmental factors affecting survival and growth, such as air humidity, soil depth, and forest tree species composition, and thus, those drivers jointly determined the realized niche of the species. Soil pH had a strong effect on the flowering probability, while the effect on λ was relatively small. In addition to identifying specific drivers for A. spicata’s population dynamics, our study illustrates the impact that spatial variation in environmental conditions can have on λ. Assessing the effects of a broad range of potential drivers, as done in this study, is important not only to quantify the relative importance of different drivers for population dynamics but also to understand species distributions and abundance patterns.

Seedling maturation drives spatial variability in demographic dynamics of an invader with multiple introductions: insights from an LTRE analysis

Multiple introductions are hypothesized to facilitate the success of invasive plant species, because they can result in novel genotypes through intraspecific hybridization potentially increasing the ability to adapt to the novel environment. In this study, we address the question of how the demography of an invader with multiple introductions and intraspecific hybridization varies across sites. This was done by modeling the population dynamics of Brazilian pepper, Schinus terebinthifolia Raddi (Anacardiaceae), a shrub native to Brazil, Paraguay and Argentina that has invaded the global subtropics and was introduced to Florida on two separate occasions. This species exhibits variability in growth form such that vertical and lateral growth are not strongly associated. Our demographic field work took place at six sites spanning the introduced range in Florida and differing in introduction history. For each site we constructed integral projection models where the probabilities of survival, growth and reproduction were modeled as functions of two different metrics of size, the continuous variables diameter and height, metrics of vertical and lateral growth, respectively. We performed a Life Table Response Experiment analysis to decompose the effects of variation among sites in vital rates on the population dynamics of S. terebinthifolia. We found that spatial variation in population dynamics was driven primarily by site-level differences in the maturation of seedlings into reproductive adults. The survival and growth of the largest individuals had the highest elasticity, suggesting that management actions capable of decreasing these vital rates would have the greatest effect on reducing the population growth rate.

Local spatial variation in the population dynamics of two tree species in a region of Atlantic Rainforest, SE Brazil

The population dynamics of species with distinct geographic distribution ranges and local abundances can be differently influenced by environmental differences at both the regional and local scales. Here, we test for local spatial variation in the dynamics of different populations of two tree species with these distinct characteristics. We took advantage of one population census and carried out a new census of two populations of Faramea picinguabae M.Gomes (Rubiaceae) and Mollinedia schottiana (Spreng.) Perkins (Monimiaceae) at two non-contiguous, permanent 1-ha plots (B and E) located at a region of Atlantic Rainforest, SE Brazil. The plots differed in declivity and soil coverage by rocky boulders. The annual population growth rate (λ) differed only for F. picinguabae (λB = 1.009, λE = 0.959), which presents restricted geographic distribution range and low local abundance in relation to M. schottiana (λB = 0.982, λE = 0.987). The decline in three out of four populations may result from a severe drought in SE Brazil in the last decade. The increase in F. picinguabae at plot B is likely a response to the lower soil coverage by rocky boulders at this plot. Even though we evaluated only two populations of two species, our conclusions open a new venue for the investigation of population dynamics. Within the same forest, some species might show spatial variation in population dynamics mediated by environmental differences at the local scale, while others might not. In the long term, differences among species are likely to result in important changes in community structure and dynamics, as well as in ecosystem functions.

Bayesian hierarchical surplus production model of the common whelk Buccinum undatum in Icelandic waters

Whelk fisheries globally suffer a from a lack of data and dearth of stock assessments, even though they are growing and can contribute important income locally in some regions. Hierarchical Bayesian methods are especially suitable for estimating biological parameters and reference points for data-poor stocks, as they can borrow strength from stocks with more information. Here we analyze the common whelk (Buccinum undatum) fishery in Iceland, which was initiated in late 1996 and is restricted to Breiðafjörður in Western Iceland. Whelk may be vulnerable to overexploitation due to low dispersal, differences in growth and maturation on small spatial scales, and limited regulation. A population dynamics model for whelk was used to test whether inclusion of spatial variation improved model fit, and demonstrates where more data are needed to improve stock assessment. We used CPUE data as an index of biomass and catches to fit a Bayesian hierarchical Schaefer surplus production model that included six sub-regions, and compared this model with all models that included successively less hierarchical structure. We also consolidated environmental and whelk demographic data from Iceland, including growth, maturity, and mortality rates, to form prior probability distributions for population growth and carrying capacity parameters. To determine whether spatial catch distribution would aid sustainability, we compared results when catches were evenly distributed over sub-regions to those based on status-quo catch distributions. The best model chosen included spatial variation in population dynamics, but more contrast in the data or additional abundance data are needed to be useful for stock assessment. As whelk is traditionally a data-poor fishery, our results yield hyperparameter distributions that can be used as prior information for assessments of whelk elsewhere, as well as sensitivity analyses that show how influential prior distributions can be on model selection and results.

The generality of management recommendations across populations of an invasive perennial herb

Demographic models are widely used to produce management recommendations for different species. For invasive plants, current management recommendations to control local population growth are often based on data from a limited number of populations per species, and the assumption of stable population structure (asymptotic dynamics). However, spatial variation in population dynamics and deviation from a stable structure may affect these recommendations, calling into question their generality across populations of an invasive species. Here, I focused on intraspecific variation in population dynamics and investigated management recommendations generated by demographic models across 37 populations of a short-lived, invasive perennial herb (Lupinus polyphyllus). Models that relied on the proportional perturbations of vital rates (asymptotic elasticities) indicated an essential role for plant survival in long-term population dynamics. The rank order of elasticities for different vital rates (survival, growth, retrogression, fecundity) varied little among the 37 study populations regardless of population status (increasing or declining asymptotically). Summed elasticities for fecundity increased, while summed elasticities for survival decreased with increasing long-term population growth rate. Transient dynamics differed from asymptotic dynamics, but were qualitatively similar among populations, that is, depending on the initial size structure, populations tended to either increase or decline in density more rapidly than predicted by asymptotic growth rate. These findings indicate that although populations are likely to exhibit transient dynamics, management recommendations based on asymptotic elasticities for vital rates might be to some extent generalised across established populations of a given short-lived invasive plant species.

Using demographic attributes from long‐term monitoring data to delineate natural population structure

Summary The concept of ‘natural’ populations is a foundation of modern ecology and conservation, with a large body of theoretical literature using these discrete demographic units to understand population dynamics and prioritize conservation strategies. To date, there are currently no objective methods for empirically delineating large‐scale population boundaries using demographic data. We present a novel approach for using large‐scale, citizen‐science monitoring data to quantify geographic structure in trend and abundance and identify distinct natural populations. We demonstrate this approach by delineating populations of eight passerine species using data collected as part of the North American Breeding Bird Survey. Our approach was able to identify geographic structure in both trend and abundance and to delineate distinct populations for all eight species. An independent validation of three species indicated this demographic variation was reflected in underlying vital rates. Synthesis and applications. Natural populations are biologically based alternatives to the traditional geographically defined units that can improve the ability of researchers and managers to quantify spatial variation in population dynamics. Our analysis of natural population structure in breeding songbirds demonstrates that species can show substantial geographic variation in population attributes and underlying demography. We recommend managers define spatial units using natural populations when setting regional population objectives for both single and multispecies conservation plans.

Improved state‐space models for inference about spatial and temporal variation in abundance from count data

Models of population dynamics are frequently used for purposes such as testing hypotheses about density dependence and predicting species' responses to future environmental change or conservation actions. Fitting models of population dynamics to field data is challenging because most data sets are characterized by observation error, which can inflate estimates of process variation if ignored. Recently, state‐space models have been developed to deal with this problem by directly modeling both the observation error and the ecological process of interest. Conventional state‐space models, however, have several important limitations: (1) they assume that random effects are Gaussian distributed, which implies that abundance can be negative and that false positive observation errors are equally likely as false negative errors; (2) they do not admit spatial variation in population dynamics; and (3) some of the parameters of the model are not estimable. We demonstrate how each of these problems can be resolved using a class of hierarchical models proposed byDail and Madsen (2011)that attributes observation error to imperfect detection. We expand this class of models to accommodate classical growth models (e.g., exponential and Ricker‐logistic), zero‐inflation, and random effects. We also present methods for forecasting population size under future environmental conditions. Implementation of these ideas is possible using either frequentist or Bayesian methods, as demonstrated by accompanying R and JAGS code. Results of a simulation study suggest that bias is negligible and coverage nominal in most cases for the proposed model extensions. An analysis of data from the North American Breeding Bird Survey highlights how these methods can be readily applied to existing data, but it also suggests that precision will be low when direct information about detection probability (such as is collected using distance sampling or replicated counts) is lacking.

Small-Scale Spatial Variation in Population Dynamics and Fishermen Response in a Coastal Marine Fishery

A major challenge for small-scale fisheries management is high spatial variability in the demography and life history characteristics of target species. Implementation of local management actions that can reduce overfishing and maximize yields requires quantifying ecological heterogeneity at small spatial scales and is therefore limited by available resources and data. Collaborative fisheries research (CFR) is an effective means to collect essential fishery information at local scales, and to develop the social, technical, and logistical framework for fisheries management innovation. We used a CFR approach with fishing partners to collect and analyze geographically precise demographic information for grass rockfish (Sebastes rastrelliger), a sedentary, nearshore species harvested in the live fish fishery on the West Coast of the USA. Data were used to estimate geographically distinct growth rates, ages, mortality, and length frequency distributions in two environmental subregions of the Santa Barbara Channel, CA, USA. Results indicated the existence of two subpopulations; one located in the relatively cold, high productivity western Channel, and another in the relatively warm, low productivity eastern Channel. We parameterized yield per recruit models, the results of which suggested nearly twice as much yield per recruit in the high productivity subregion relative to the low productivity subregion. The spatial distribution of fishing in the two environmental subregions demonstrated a similar pattern to the yield per recruit outputs with greater landings, effort, and catch per unit effort in the high productivity subregion relative to the low productivity subregion. Understanding how spatial variability in stock dynamics translates to variability in fishery yield and distribution of effort is important to developing management plans that maximize fishing opportunities and conservation benefits at local scales.

Explaining Spatial Heterogeneity in Population Dynamics and Genetics from Spatial Variation in Resources for a Large Herbivore

Fine-scale spatial variation in genetic relatedness and inbreeding occur across continuous distributions of several populations of vertebrates; however, the basis of observed variation is often left untested. Here we test the hypothesis that prior observations of spatial patterns in genetics for an island population of feral horses (Sable Island, Canada) were the result of spatial variation in population dynamics, itself based in spatial heterogeneity in underlying habitat quality. In order to assess how genetic and population structuring related to habitat, we used hierarchical cluster analysis of water sources and an indicator analysis of the availability of important forage species to identify a longitudinal gradient in habitat quality along the length of Sable Island. We quantify a west-east gradient in access to fresh water and availability of two important food species to horses: sandwort, Honckenya peploides, and beach pea, Lathyrus japonicas. Accordingly, the population clusters into three groups that occupy different island segments (west, central, and east) that vary markedly in their local dynamics. Density, body condition, and survival and reproduction of adult females were highest in the west, followed by central and east areas. These results mirror a previous analysis of genetics, which showed that inbreeding levels are highest in the west (with outbreeding in the east), and that there are significant differences in fixation indices among groups of horses along the length of Sable Island. Our results suggest that inbreeding depression is not an important limiting factor to the horse population. We conclude that where habitat gradients exist, we can anticipate fine-scale heterogeneity in population dynamics and hence genetics.

Population processes in European Blackbirds Turdus merula: a state–space approach

Understanding the demographic processes driving populations is critical in formulating effective management plans. State–space models offer an appealing framework in which to construct models to examine temporal and spatial variation in population dynamics, as they make efficient use of the varied sources of data available. We develop a Bayesian state–space model of the population dynamics of European Blackbird Turdus merula using data collected as part of the British Trust for Ornithology’s Integrated Population Monitoring programme. Previous models of similar data have concentrated on simultaneous estimation of abundance and survival parameters and we extend this approach by incorporating the direct estimation of brood size and nesting success. We show that annual population change is most correlated with adult survival, but that population processes appear to differ in eastern and western regions of Britain which themselves differ markedly in their landscape composition.

Larval recruitment in a region of strong, persistent upwelling and recruitment limitation

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 394:79-99 (2009) - DOI: https://doi.org/10.3354/meps08216 Larval recruitment in a region of strong, persistent upwelling and recruitment limitation Steven G. Morgan1,2,*, Jennifer L. Fisher1, Amber J. Mace1,3 1Bodega Marine Laboratory, University of California Davis, 2099 Westside Drive, PO Box 247, Bodega Bay, California 94923-0247, USA 2Department of Environmental Science and Policy, University of California Davis, 1 Shields Avenue, Davis, California 93510, USA 3Present address: California Ocean Science Trust, 1330 Broadway, Suite 1135, Oakland, California 94612-2530, USA *Email: sgmorgan@ucdavis.edu ABSTRACT: Larvae are thought to be highly vulnerable to offshore transport of upwelling regions, limiting recruitment to infrequent wind relaxation and downwelling events. However, larvae could also be transported onshore by upwelled bottom waters, onshore wind-forcing or internal tides throughout the water column. We determined the relative importance of these hypothetical mechanisms for the timing of recruitment of 8 invertebrate taxa during the peak upwelling season in a region of strong, persistent upwelling. Recruitment was determined for 5 yr at an open embayment near the surface and bottom of the water column to examine the interaction of behavioral and physical processes regulating larval recruitment. Postlarvae consistently recruited near the surface or near the bottom depending on the species. Onshore delivery of larvae during wind relaxations and reversals did not best explain recruitment patterns in our area for most taxa. Only mussels consistently recruited more during these events, and they recruited in bottom rather than surface waters. Six crab taxa recruited primarily during upwelling. Recruitment of 7 taxa was intermittently correlated with the maximum tidal range, suggesting that internal waves also may deliver larvae onshore. Thus larvae may recruit by multiple processes in upwelling regions rather than being limited to infrequent relaxation events, leaving the mechanisms responsible for observed spatial patterns in larval recruitment and adult densities unexplained. Comprehensive studies of the behavioral and physical processes underlying larval recruitment and post-settlement mortality are needed to explain observed temporal and spatial variation in population dynamics and community structure in upwelling regions. KEY WORDS: Larval recruitment · Recruitment limitation · Larval transport · Upwelling · Population dynamics · Community structure Full text in pdf format PreviousNextCite this article as: Morgan SG, Fisher JL, Mace AJ (2009) Larval recruitment in a region of strong, persistent upwelling and recruitment limitation. Mar Ecol Prog Ser 394:79-99. https://doi.org/10.3354/meps08216 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 394. Online publication date: November 18, 2009 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2009 Inter-Research.

Spatial variation in population dynamics of juvenile Atlantic salmon: implications for conservation and management

Application of habitat models for predicting expected local densities of Atlantic Salmon Salmo salar in healthy populations has been hampered by a lack of generality in their fit to data from different systems. It is believed that this problem results at least in part from difficulties of effectively integrating factors that act across a range of spatial and temporal scales. Here, as an aid to developing more robust modelling and sampling methodologies, a simple process‐based model for local‐scale dynamics of Atlantic salmon juveniles is developed from first principles by integrating contemporary understanding of self‐thinning, density‐dependent growth and dispersal. The aim is to present a readily understood structure to illustrate the links between spawning and stocking strategies, habitat, migration and fish production. Based on this structure, contemporary understanding of the more complex biological processes that affect density, growth and habitat are discussed in relation to some of the key requirements of managers, including stocking for rehabilitation, assessment of predation impact and development of strategies for sampling populations effectively when deriving habitat‐production models. A major conclusion is that more structured, integrated research is required to provide the basic variables needed to model links between local and global scale habitat and fish production effectively. Nevertheless, application of the current understanding of the biology of Atlantic salmon should be of great benefit to managers in extracting key information from field surveys.

Spatial Variation in Population Dynamics of Sitka Mice in Floodplain Forests

Population dynamics and demography of the Sitka mouse, Peromyscus keeni sitkensis, were studied by mark-recapture live-trapping over a 4-year period in four floodplain and upland forest habitats: old-growth Sitka spruce (Picea sitchensis) floodplain; red alder (Alnus rubra) floodplain; beaver-pond floodplain; and nearby old-growth Sitka spruce-western hemlock (Tsuga heterophylla) upland forest. We did not find the expected source-sink population dynamics resulting from flood disturbance or between-habitat variation in food resources. We found significant between-year differences (P < 0.05) in population densities, age and sex ratios, survival rates, growth rates, and movements. Within-year differences in all demographic variables were consistently greater between replicate trapping grids within habitat types than between habitat types, and there was no year-to-year consistency in any demographic difference between replicates or habitat types. We conclude that floodplain forests, per se, do not provide unique habitat for Sitka mice in either a strongly positive or negative sense compared with upland old-growth forests.

Dynamics of Metapopulations of Small Mammals

This paper reviews the development and application of the metapopulation concept to mammalian population dynamics. Studies of mammalian population dynamics documenting spatial variation in demography contributed importantly to the evolution of a landscape approach to ecology. At the same time, important theoretical developments such as the theory of island biogeography and Levin's metapopulation model provided ecologists with testable hypotheses regarding spatial variation in population dynamics. Empirical studies of mammalian populations indicate a spectrum of spatial structures from large homogeneous populations integrated by dispersal to highly isolated populations not connected by dispersal. The metapopulation approach to mammalian population dynamics resolves some of the earlier controversy regarding the nature of regulation of populations. It has also contributed importantly to the conservation biology of mammals.

A metapopulation approach to the population biology of the Song Sparrow Melospiza melodia

In this paper, we describe spatial variation in the demography of the Song Sparrow Melospiza melodia. Long‐term population studies of birds have generally considered only single sites in optimal habitat, but recent theory has shown the value of taking spatial variation in population dynamics into account. In this theory, collections of local populations in habitat patches connected by dispersal are denned as metapopulations. We review metapopulation models briefly and then use these ideas in a study of the Song Sparrow. Sparrows were studied on islands of varying size and degree of isolation from the North American continent. For analysis, these islands are grouped into three areas. Sparrows on the isolated Mandarte Island usually reproduced and survived well over 17 years but suffered from catastrophic mortality in some winters. After such events, the population recovered quickly without much immigration. Sparrows on smaller islets near Mandarte also survived and reproduced well during 4 years, and they did not experience severe mortality in a winter in which those on Mandarte declined by over 90%. These small islets frequently exchanged first year birds, but only one yearling bird moved between the small islets and the more isolated Mandarte. Sparrows at one of two sites on the larger Westham Island, near the continental mainland, survived less well than on the small offshore islands. Reproduction on Westham Island was poor because of frequent nest failure and high levels of brood parasitism by Brown‐headed Cowbirds Molothrus ater. Despite this poor reproduction and survival, the Westham population remained stable as a result of immigration. We interpret the dynamics of these sparrow populations in terms of H. R. Pulliam's source‐sink metapopulation model.