scholarly journals Beyond demographic buffering: Context dependence in demographic strategies across animals

2021 ◽  
Author(s):  
Omar Lenzi ◽  
Arpat Ozgul ◽  
Roberto Salguero-Gomez ◽  
Maria Paniw
Keyword(s):  
Growth Rate ◽  
Population Growth ◽  
Temporal Variation ◽  
Population Growth Rate ◽  
Natural Populations ◽  
Environmental Context ◽  
Context Dependence ◽  
Vital Rate ◽  
Rate Variation ◽  
Vital Rates

Temporal variation in vital rates (e.g., survival, reproduction) can decrease the long-term mean performance of a population. Species are therefore expected to evolve demographic strategies that counteract the negative effects of vital rate variation on the population growth rate. One key strategy, demographic buffering, is reflected in a low temporal variation in vital rates critical to population dynamics. However, comparative studies in plants have found little evidence for demographic buffering, and little is known about the prevalence of buffering in animal populations. Here, we used vital rate estimates from 31 natural populations of 29 animal species to assess the prevalence of demographic buffering. We modeled the degree of demographic buffering using a standard measure of correlation between the standard deviation of vital rates and the sensitivity of the population growth rate to changes in such vital rates across populations. We also accounted for the effects of life-history traits, i.e., age at first reproduction and spread of reproduction across the life cycle, on these correlation measures. We found no strong or consistent evidence of demographic buffering across the study populations. Instead, key vital rates could vary substantially depending on the specific environmental context populations experience. We suggest that it is time to look beyond concepts of demographic buffering when studying natural populations towards a stronger focus on the environmental context-dependence of vital-rate variation.

scholarly journals The demographic buffering strategy has a threshold of effectiveness to increases in environmental stochasticity

2020 ◽  
Author(s):  
R.C. Rodríguez-Caro ◽  
P. Capdevila ◽  
E. Graciá ◽  
J. M. Barbosa ◽  
A. Giménez ◽  
...  
Keyword(s):  
Growth Rate ◽  
Population Growth ◽  
Temporal Variation ◽  
Population Growth Rate ◽  
Environmental Stochasticity ◽  
Environmental Data ◽  
Vital Rate ◽  
Environmental Drivers ◽  
List Type ◽  
Animal Populations

AbstractAnimal populations have developed multiple strategies to deal with environmental change. Among them, the demographic buffering strategy consists on constraining the temporal variation of the vital rate(s) (e.g., survival, growth, reproduction) that most affect(s) the overall performance of the population. Given the increase in environmental stochasticity of the current global change scenario, identifying the thresholds beyond which populations are not able to remain viable -despite their potential buffering strategies- is of utmost importance.Tortoises are known to buffer the temporal variation in survival (i.e. this vital rate has the highest contribution to the population growth rate λ) at the expense of a high variability on reproductive rates (lowest contribution to λ). To identify the potential threshold in buffering ability, here we use field data collected across a decade on 15 locations of Testudo graeca along South-Eastern Spain. We analyse the effects of environmental variables (precipitation, temperature, and NDVI) on the probability of laying eggs and the number of eggs per clutch. Finally, we couple the demographic and environmental data to parametrise integral projection models (IPMs) to simulate the effects of different scenarios of drought recurrence on population growth rate.We find that droughts negatively affect the probability of laying eggs, but the overall effects on the population growth rates of T. graeca under the current drought frequencies (one per decade) are negligible. However, increasing the annual frequency of droughts decreases the buffering ability of T. graeca populations, with a threshold at three droughts per decade.Although some species may buffer current environmental regimes by carefully orchestrating how their vital rates vary through time, a demographic buffering strategy may alone not warrant population viability in extreme regimes. Our findings support the hypothesis that the buffering strategy indeed has a threshold of effectiveness. Our methodological approach also provides a useful pipeline for ecologists and managers to determine how effective the management of environmental drivers can be for demographically buffering populations, and which scenarios may not provide long-term species persistence.

Population dynamics of an Egyptian desert shrub, Thymelaea hirsuta

1997 ◽  
Vol 75 (12) ◽  
pp. 2027-2037 ◽  
Author(s):  
Ali El-Keblawy ◽  
K. H. Shaltout ◽  
J. Lovett-Doust ◽  
A. Ramadan
Keyword(s):  
Growth Rate ◽  
Population Growth ◽  
Population Growth Rate ◽  
Seedling Recruitment ◽  
Natural Populations ◽  
Plant Size ◽  
Population Variation ◽  
Adult Survival ◽  
Thymelaea Hirsuta ◽  
Egyptian Desert

Natural populations of the evergreen shrub, Thymelaea hirsuta (L.) Endl., were studied over 6 years at five desert habitats, in terms of seedling recruitment and adult survival and as a function of plant size and gender class. Habitat and time significantly influenced mortality of both reproductive and non-reproductive plants. Plant size also significantly affected adult mortality. Seedling recruitment varied significantly with habitat and year and approached zero some years. Significant among-year and among-population variation in population growth rates were observed over the 6 years of study, and all populations declined in size (ranging from −1.7% per year at the coastal dune site to −10.9% per year at the inland plateau site). Spearman rank correlation analysis between habitats ranked according to a north–south gradient and demographic variables indicates that this gradient is associated with a pattern of lower seedling emergence and survival and a lower population growth rate and greater mortality for all size-classes of Thymelaea plants. In experimental botanic garden plots, germination of seed collected from five natural populations, and seedling survival in the following year were assessed under conditions of high, medium, and low seedling density. Seedling emergency differed significantly according to maternal habitat. With regular watering, seeding survival to one year was 72% (averaged across habitats and densities). This compares with 64% for seedlings grown at the highest density, suggesting that the intense mortality observed under field conditions is more likely to be a result of water shortage than intraspecific competition. Key words: Egyptian desert, Thymelaea hirsuta, germination and establishment, seedlings, recruitment, competition, population growth rate.

scholarly journals Warming, soil moisture, and loss of snow increase Bromus tectorum’s population growth rate

Elem Sci Anth ◽  
2014 ◽  
Vol 2 ◽  
Author(s):  
Aldo Compagnoni ◽  
Peter B. Adler
Keyword(s):  
Growth Rate ◽  
Population Growth ◽  
Snow Cover ◽  
Population Growth Rate ◽  
Experimental Manipulation ◽  
Direct Effects ◽  
Vital Rates ◽  
Positive Effects ◽  
The North ◽  
Increasing Temperature

Abstract Climate change threatens to exacerbate the impacts of invasive species. In temperate ecosystems, direct effects of warming may be compounded by dramatic reductions in winter snow cover. Cheatgrass (Bromus tectorum) is arguably the most destructive biological invader in basins of the North American Intermountain West, and warming could increase its performance through direct effects on demographic rates or through indirect effects mediated by loss of snow. We conducted a two-year experimental manipulation of temperature and snow pack to test whether 1) warming increases cheatgrass population growth rate and 2) reduced snow cover contributes to cheatgrass’ positive response to warming. We used infrared heaters operating continuously to create the warming treatment, but turned heaters on only during snowfalls for the snowmelt treatment. We monitored cheatgrass population growth rate and the vital rates that determine it: emergence, survival and fecundity. Growth rate increased in both warming and snowmelt treatments. The largest increases occurred in warming plots during the wettest year, indicating that the magnitude of response to warming depends on moisture availability. Warming increased both fecundity and survival, especially in the wet year, while snowmelt contributed to the positive effects of warming by increasing survival. Our results indicate that increasing temperature will exacerbate cheatgrass impacts, especially where warming causes large reductions in the depth and duration of snow cover.

Effects of territorial status and life history on Sandhill Crane (Antigone canadensis) population dynamics in south-central Wisconsin, USA

2019 ◽  
Vol 97 (2) ◽  
pp. 112-120 ◽  
Author(s):  
Michael E. Wheeler ◽  
Jeb A. Barzen ◽  
Shawn M. Crimmins ◽  
Timothy R. Van Deelen
Keyword(s):  
Growth Rate ◽  
Population Growth ◽  
Population Growth Rate ◽  
Demographic Data ◽  
Bird Species ◽  
Adult Survival ◽  
Vital Rates ◽  
Management Actions ◽  
South Central ◽  
Sandhill Cranes

Population growth rate in long-lived bird species is often most sensitive to changes in adult survival. Sandhill Cranes (Antigone canadensis (Linnaeus, 1758)) have long life spans, small broods, and delayed first reproduction. Only territorial adult Sandhill Cranes participate in breeding, and territory acquisition reflects the interplay between the availability of suitable territories and the variation in mortality of adult birds occupying those territories. We estimated vital rates of a population at equilibrium using long-term resightings data (2000–2014; n = 451 marked individuals) in a multistate mark–resight model and used a stage-structured projection matrix to assess how strongly territorial adult survival affects population growth rate. Elasticity analysis indicated territorial birds surviving and retaining territories had a 2.58 times greater impact on population growth compared with the next most important transition rate (survival of nonterritorial adults remaining nonterritorial). Knowing how changes in vital rates of various stage classes will differentially impact population growth rate allows for targeted management actions including encouraging growth in recovering populations, assessing opportunity for recreational harvest, or maintaining populations at a desired level. This study also highlights the value of collecting demographic data for all population segments, from which one can derive reproductive output or growth rate.

scholarly journals Drivers of large-scale spatial demographic variation in a perennial plant

2020 ◽  
Author(s):  
Gesa Römer ◽  
Ditte M. Christiansen ◽  
Hendrik de Buhr ◽  
Kristoffer Hylander ◽  
Owen R. Jones ◽  
...  
Keyword(s):  
Growth Rate ◽  
Population Dynamics ◽  
Environmental Factors ◽  
Population Growth ◽  
Spatial Variation ◽  
Population Growth Rate ◽  
Forest Understory ◽  
Environmental Drivers ◽  
Vital Rates ◽  
The Impact

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 the vital rates (survival, growth and reproduction), and explore these relationships over large geographical areas and long environmental gradients. In this study, we examined the effects of a broad variety of abiotic and biotic environmental factors, including intraspecific density, 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 effect 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 population growth rate 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.

scholarly journals Spatiotemporal dynamics in vital rates of Humboldt’s flying squirrels and Townsend’s chipmunks in a late-successional forest

2019 ◽  
Vol 101 (1) ◽  
pp. 187-198
Author(s):  
Matt Weldy ◽  
Clinton W Epps ◽  
Damon B Lesmeister ◽  
Tom Manning ◽  
Eric D Forsman
Keyword(s):  
Growth Rate ◽  
Population Growth ◽  
Pacific Northwest ◽  
Population Growth Rate ◽  
Habitat Associations ◽  
Spatiotemporal Variability ◽  
Life History Strategies ◽  
Vital Rates ◽  
Annual Survival ◽  
Flying Squirrels

Abstract Knowledge of the spatiotemporal variability of abundance and vital rates is essential to the conservation of wildlife populations. In Pacific Northwest forests, previous small mammal research has focused on estimating abundance; few studies have focused on vital rates. We used robust design temporal symmetry models and live-trapping data collected 2011–2016 at nine sites to estimate apparent annual survival, population growth rate, and recruitment of Humboldt’s flying squirrels (Glaucomys oregonensis) and Townsend’s chipmunks (Neotamias townsendii) in a late-successional forest of the Cascade Mountains of Oregon, United States. We also estimated the proportional contribution of apparent annual survival and recruitment to population growth rate. Covariates previously associated with abundance were also associated with vital rates for Townsend’s chipmunks, but less so for Humboldt’s flying squirrels. Apparent annual survival was nearly constant (range = 0.47 to 0.51) among years and sites for Humboldt’s flying squirrels but was consistently lower and more variable among years for Townsend’s chipmunks (range = 0.13 to 0.31). Recruitment was variable among years for both species. Apparent annual survival generally contributed more than recruitment to the population growth rate of Humboldt’s flying squirrels. For Townsend’s chipmunks, recruitment consistently contributed more than apparent annual survival to population growth rate. These findings suggest that life history strategies differed for these co-occurring species. This study demonstrates substantial temporal variation in vital rates and some differences in abundance and vital rate habitat associations, suggesting that habitat suitability inferences based on short time series or variation in abundance could be misleading.

scholarly journals Demographic analysis of the shortfin mako shark, Isurus oxyrinchus, in the Northwest Pacific using a two-sex stage-based matrix model

2014 ◽  
Vol 71 (7) ◽  
pp. 1604-1618 ◽  
Author(s):  
Wen-Pei Tsai ◽  
Chi-Lu Sun ◽  
André E. Punt ◽  
Kwang-Ming Liu
Keyword(s):  
Growth Rate ◽  
Population Growth ◽  
Matrix Model ◽  
Population Growth Rate ◽  
Future Research ◽  
Northwest Pacific ◽  
Vital Rates ◽  
Mako Shark ◽  
Shortfin Mako ◽  
The Impact

Most demographic models are single sex, and assume both sexes have the same vital rates. However, many species, including the shortfin mako shark, are sexually dimorphic in vital rates, which suggests the need for two-sex models. In this study, a two-sex stage-structured matrix model was constructed to estimate shortfin mako shark demography and population dynamics. Monte Carlo simulations were used to evaluate the impact of uncertainties on the estimate of population growth rate. The number of shortfin mako sharks is found to be dropping under current conditions, but will stabilize if size-limit management is implemented. The simulations indicated that population growth rate estimates are mainly influenced by the uncertainty related to survival rate and fecundity. The effects of uncertainty regarding the age at maturity and longevity were found to be relatively minor. Future research should focus on obtaining estimates of natural mortality and reproductive traits for this species to improve the accuracy of demographic estimates.

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