scholarly journals A modelling exercise to show why population models should incorporate distinct life histories of dispersers

2018 ◽  
Author(s):  
Jacques A. Deere ◽  
Ilona van den Berg ◽  
Gregory Roth ◽  
Isabel M. Smallegange
Keyword(s):  
Life History ◽  
Population Growth ◽  
Life Histories ◽  
Population Level ◽  
Population Models ◽  
Integral Projection Model ◽  
Projection Model ◽  
Individual Level ◽  
Population Growth Rates ◽  
Dispersal Probability

AbstractDispersal is an important form of movement influencing population dynamics, species distribution, and gene flow between populations. In population models, dispersal is often included in a simplified manner by removing a random proportion of the population. Many ecologists now argue that models should be formulated at the level of individuals instead of the population-level. To fully understand the effects of dispersal on natural systems, it is therefore necessary to incorporate individual-level differences in dispersal behaviour in population models. Here we parameterised an integral projection model (IPM), which allows for studying how individual life histories determine population-level processes, using bulb mites, Rhizoglyphus robini, to assess to what extent dispersal expression (frequency of individuals in the dispersal stage) and dispersal probability affect the proportion of dispersers and natal population growth rate. We find that allowing for life-history differences between resident phenotypes and disperser phenotypes shows that multiple combinations of dispersal probability and dispersal expression can produce the same proportion of leaving individuals. Additionally, a given proportion of dispersing individuals results in different natal population growth rates. The results highlight that dispersal life histories, and the frequency with which disperser phenotypes occur in the natal population, significantly affect population-level processes. Thus, biological realism of dispersal population models can be increased by incorporating the typically observed life history differences between resident phenotypes and disperser phenotypes, and we here present a methodology to do so.

Example Four: Facultative Anadromy in Salmonid Fishes

2020 ◽  
pp. 86-92
Keyword(s):  
Life History ◽  
Life Histories ◽  
Population Level ◽  
Dynamic State ◽  
Salmonid Fishes ◽  
Individual Level ◽  
State Variable ◽  
Level Model ◽  
Fitness Benefits ◽  
The Individual

This chapter offers a fourth example model, with the objective of (1) illustrating the application of state- and prediction-based theory (SPT) to a new kind of decision—a life history decision—in a case where dynamic state variable modeling (DSVM) has been applied successfully; and (2) describing the unique ability of models utilizing SPT to address population-level questions of particular interest to conservationists and managers. In this case, SPT produced individual-level decisions similar to those of DSVM, but including them in a population-level model led to quite different conclusions than those implied by the individual-level DSVM analysis. Salmonid fishes exhibit amazing life history diversity. One fundamental distinction among salmonid life histories is whether or not individuals migrate to the ocean. In general, facultative anadromy can be seen as an adaptive behavior that trades off the fitness benefits of going to the ocean versus those of remaining resident. The anadromy versus residency decision is important to fish conservation and resource management.

Demography of Xenosaurus platyceps (Squamata: Xenosauridae): a comparison between tropical and temperate populations

2008 ◽  
Vol 29 (2) ◽  
pp. 245-256 ◽  
Author(s):  
Carissa Jones ◽  
Isaac Rojas-González ◽  
Julio Lemos-Espinal ◽  
Jaime Zúñiga-Vega
Keyword(s):  
Life History ◽  
Population Growth ◽  
Adult Mortality ◽  
Life History Strategies ◽  
Relative Importance ◽  
Theoretical Frameworks ◽  
Population Growth Rates ◽  
Relative Contribution ◽  
Two Populations ◽  
Average Fitness

Abstract There appears to be variation in life-history strategies even between populations of the same species. For ectothermic organisms such as lizards, it has been predicted that demographic and life-history traits should differ consistently between temperate and tropical populations. This study compares the demographic strategies of a temperate and a tropical population of the lizard Xenosaurus platyceps. Population growth rates in both types of environments indicated populations in numerical equilibrium. Of the two populations, we found that the temperate population experiences lower adult mortality. The relative importance (estimated as the relative contribution to population growth rate) of permanence and of the adult/reproductive size classes is higher in the temperate population. In contrast, the relative importance for average fitness of fecundity and growth is higher in the tropical population. These results are consistent with the theoretical frameworks about life-historical differences among tropical and temperate lizard populations.

Assessment of invasive rodent impacts on island avifauna: methods, limitations and the way forward

2015 ◽  
Vol 42 (2) ◽  
pp. 185 ◽  
Author(s):  
Lise Ruffino ◽  
Diane Zarzoso-Lacoste ◽  
Eric Vidal
Keyword(s):  
Population Growth ◽  
Population Level ◽  
Bird Conservation ◽  
Bird Population ◽  
Breeding Parameters ◽  
Population Growth Rates ◽  
Bird Populations ◽  
Field Evidence ◽  
Bird Breeding

Bird conservation is nowadays a strong driving force for prioritising rodent eradications, but robust quantitative estimates of impacts are needed to ensure cost-effectiveness of management operations. Here, we review the published literature to investigate on what methodological basis rodent effects on island bird communities have been evaluated for the past six decades. We then discuss the advantages and limitations of each category of methods for the detection and quantification of impacts, and end with some recommendations on how to strengthen current approaches and extend our knowledge on the mechanisms of impacts. Impact studies (152 studies considered) emphasised seabirds (67%), black rats (63%) and the Pacific Ocean (57%). Among the most commonly used methods to study rodent impacts on birds were the observation of dead eggs or empty nests while monitoring bird breeding success, and the analyses of rodent diets, which can both lead to misleading conclusions if the data are not supported by direct field evidence of rodent predation. Direct observations of rodent–bird interactions (19% of studies) are still poorly considered despite their potential to reveal cryptic behaviours and shed light on the mechanisms of impacts. Rodent effects on birds were most often measured as a change or difference in bird breeding parameters (74% of studies), while estimates of bird population growth rates (4%) are lacking. Based on the outcomes of this literature review, we highlight the need for collecting unbiased population-level estimates of rodent impacts, which are essential prerequisites for predicting bird population growth scenarios and prioritising their conservation needs. This could be achieved by a more systematic integration of long-term monitoring of bird populations into rodent management operations and modelling bird population dynamics. We also strongly recommend including various complementary methods in impact assessment strategies to unravel complex interactions between rodents and birds and avoid faulty evidence. Finally, more research should be devoted to a better understanding of the cases of non-impacts (i.e. long-term coexistence) and those impacts mediated by mechanisms other than predation and ecosystem-level processes.

Life history and environmental influences on population dynamics in sockeye salmon

2014 ◽  
Vol 71 (8) ◽  
pp. 1198-1208 ◽  
Author(s):  
Douglas C. Braun ◽  
John D. Reynolds
Keyword(s):  
Population Dynamics ◽  
Life History ◽  
Population Growth ◽  
Growth Rates ◽  
Environmental Conditions ◽  
Sockeye Salmon ◽  
Life History Traits ◽  
Relative Importance ◽  
Population Growth Rates ◽  
Habitat Variables

Understanding linkages among life history traits, the environment, and population dynamics is a central goal in ecology. We compared 15 populations of sockeye salmon (Oncorhynchus nerka) to test general hypotheses for the relative importance of life history traits and environmental conditions in explaining variation in population dynamics. We used life history traits and habitat variables as covariates in mixed-effect Ricker models to evaluate the support for correlates of maximum population growth rates, density dependence, and variability in dynamics among populations. We found dramatic differences in the dynamics of populations that spawn in a small geographical area. These differences among populations were related to variation in habitats but not life history traits. Populations that spawned in deep water had higher and less variable population growth rates, and populations inhabiting streams with larger gravels experienced stronger negative density dependence. These results demonstrate, in these populations, the relative importance of environmental conditions and life histories in explaining population dynamics, which is rarely possible for multiple populations of the same species. Furthermore, they suggest that local habitat variables are important for the assessment of population status, especially when multiple populations with different dynamics are managed as aggregates.

scholarly journals Range expansion is associated with increased survival and fecundity in a long-lived bat species

2019 ◽  
Vol 286 (1906) ◽  
pp. 20190384 ◽  
Author(s):  
P.-L. Jan ◽  
L. Lehnen ◽  
A.-L. Besnard ◽  
G. Kerth ◽  
M. Biedermann ◽  
...  
Keyword(s):  
Life History ◽  
Population Growth ◽  
Range Expansion ◽  
Empirical Studies ◽  
Simulated Data ◽  
Adult Survival ◽  
Juvenile Survival ◽  
Average Growth ◽  
Population Growth Rates ◽  
Expanding Population

The speed and dynamics of range expansions shape species distributions and community composition. Despite the critical impact of population growth rates for range expansion, they are neglected in existing empirical studies, which focus on the investigation of selected life-history traits. Here, we present an approach based on non-invasive genetic capture–mark–recapture data for the estimation of adult survival, fecundity and juvenile survival, which determine population growth. We demonstrate the reliability of our method with simulated data, and use it to investigate life-history changes associated with range expansion in 35 colonies of the bat species Rhinolophus hipposideros . Comparing the demographic parameters inferred for 19 of those colonies which belong to an expanding population with those inferred for the remaining 16 colonies from a non-expanding population reveals that range expansion is associated with higher net reproduction. Juvenile survival was the main driver of the observed reproduction increase in this long-lived bat species with low per capita annual reproductive output. The higher average growth rate in the expanding population was not associated with a trade-off between increased reproduction and survival, suggesting that the observed increase in reproduction stems from a higher resource acquisition in the expanding population. Environmental conditions in the novel habitat hence seem to have an important influence on range expansion dynamics, and warrant further investigation for the management of range expansion in both native and invasive species.

scholarly journals Slow Life History Leaves Endangered Snake Vulnerable to Illegal Poaching

2020 ◽  
Author(s):  
Chris Jolly ◽  
Brenton von Takach ◽  
Jonathan Webb
Keyword(s):  
Life History ◽  
Population Growth ◽  
Life Histories ◽  
Extinction Risk ◽  
Adult Mortality ◽  
Sensitivity Analyses ◽  
Wildlife Trade ◽  
Pet Trade ◽  
The Impact ◽  
Negative Population

Abstract Global wildlife trade is a multibillion-dollar industry and a significant driver of vertebrate extinction risk. Yet, few studies have quantified the impact of wild harvesting for the illicit pet trade on populations. Long-lived species, by virtue of their slow life history characteristics, may be unable to sustain even low levels of harvesting. Here, we assessed the impact of illegal poaching on a metapopulation of endangered broad-headed snakes (Hoplocephalus bungaroides) at gated (protected) and ungated (unprotected) populations. Because broad-headed snakes are long-lived, grow slowly and reproduce infrequently, populations are likely vulnerable to increases in adult mortality. Long-term data revealed that annual survival rates of snakes were significantly lower in the ungated population than the gated population, consistent with the hypothesis of human removal of snakes for the pet trade. Population viability analysis showed that the ungated population has a strongly negative population growth rate and is only prevented from ultimate extinction by dispersal of small numbers of individuals from the gated population. Sensitivity analyses showed that the removal of a small number of adult females was sufficient to impose negative population growth and suggests that threatened species with slow life histories are likely to be especially vulnerable to illegal poaching.

scholarly journals Do we need demographic data to forecast plant population dynamics?

2015 ◽  
Author(s):  
Andrew T. Tredennick ◽  
Mevin B. Hooten ◽  
Peter B. Adler
Keyword(s):  
Environmental Change ◽  
Forecast Accuracy ◽  
Population Level ◽  
Population Models ◽  
Demographic Model ◽  
Percent Cover ◽  
Climate Effects ◽  
Individual Level ◽  
Level Data ◽  
Significant Difference

1. Rapid environmental change has generated growing interest in forecasts of future population trajectories. Traditional population models built with detailed demographic observations from one study site can address the impacts of environmental change at particular locations, but are difficult to scale up to the landscape and regional scales relevant to management decisions. An alternative is to build models using population-level data that are much easier to collect over broad spatial scales than individual-level data. However, it is unknown whether models built using population-level data adequately capture the effects of density-dependence and environmental forcing that are necessary to generate skillful forecasts. 2. Here, we test the consequences of aggregating individual responses when forecasting the population states (percent cover) and trajectories of four perennial grass species in a semi-arid grassland in Montana, USA. We parameterized two population models for each species, one based on individual-level data (survival, growth and recruitment) and one on population-level data (percent cover), and compared their forecasting accuracy and forecast horizons with and without the inclusion of climate covariates. For both models, we used Bayesian ridge regression to weight the influence of climate covariates for optimal prediction. 3. In the absence of climate effects, we found no significant difference between the forecast accuracy of models based on individual-level data and models based on population-level data. Climate effects were weak, but increased forecast accuracy for two species. Increases in accuracy with climate covariates were similar between model types. 4. In our case study, percent cover models generated forecasts as accurate as those from a demographic model. For the goal of forecasting, models based on aggregated individual-level data may offer a practical alternative to data-intensive demographic models. Long time series of percent cover data already exist for many plant species. Modelers should exploit these data to predict the impacts of environmental change.

A dynamic energy budget–integral projection model (DEB-IPM) to predict population-level dynamics based on individual data: a case study using the small and rapidly reproducing species Engraulis japonicus

2020 ◽  
Vol 71 (4) ◽  
pp. 461
Author(s):  
Baochao Liao ◽  
Xiujuan Shan ◽  
Can Zhou ◽  
Yanan Han ◽  
Yunlong Chen ◽  
...  
Keyword(s):  
Energy Budget ◽  
Environmental Changes ◽  
Population Level ◽  
Model Parameters ◽  
Integral Projection Model ◽  
Dynamic Energy Budget ◽  
Projection Model ◽  
Engraulis Japonicus ◽  
Integral Projection ◽  
Primary Model

The coupling of a dynamic energy budget (DEB) model with an integral projection model (IPM; i.e. generating a DEB-IPM) is a promising new method to predict the population-level dynamics of species based on individuals. In a single framework, the DEB component provides links to the individual-level physiological processes, and the IPM component provides an alternative way to investigate ecological changes in quantitative life history characteristics and population dynamics. In this paper we present a DEB-IPM to analyse a Japanese anchovy (Engraulis japonicus) population in Chinese seas. The coupled model describes the dynamics of a population of individuals, where each individual follows an energy budget. Primary model parameters (e.g. energy conductance, ὺ; allocation coefficient, κ; and volume-specific somatic maintenance, [ṗM]) were estimated. The mean population growth rate (rp) was calculated to be 3.4year–1. The predicted demographic rates (e.g. growth, survival and reproduction) were well within observed ranges, and fit within average recorded values, and captured known seasonal trends. DEB-IPMs could be a useful tool to capture the dynamics of biodiversity amidst global environmental changes.

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