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.

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 Breeding transients in capture–recapture modeling and their consequences for local population dynamics

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Daniel Oro ◽  
Daniel F. Doak
Keyword(s):  
Growth Rate ◽  
Population Dynamics ◽  
Population Growth ◽  
Population Growth Rate ◽  
Local Population ◽  
Environmental Stochasticity ◽  
Adult Survival ◽  
Local Survival ◽  
First Reproduction ◽  
Capture Recapture

Abstract Standard procedures for capture–mark–recapture modelling (CMR) for the study of animal demography include running goodness-of-fit tests on a general starting model. A frequent reason for poor model fit is heterogeneity in local survival among individuals captured for the first time and those already captured or seen on previous occasions. This deviation is technically termed a transience effect. In specific cases, simple, uni-state CMR modeling showing transients may allow researchers to assess the role of these transients on population dynamics. Transient individuals nearly always have a lower local survival probability, which may appear for a number of reasons. In most cases, transients arise due to permanent dispersal, higher mortality, or a combination of both. In the case of higher mortality, transients may be symptomatic of a cost of first reproduction. A few studies working at large spatial scales actually show that transients more often correspond to survival costs of first reproduction rather than to permanent dispersal, bolstering the interpretation of transience as a measure of costs of reproduction, since initial detections are often associated with first breeding attempts. Regardless of their cause, the loss of transients from a local population should lower population growth rate. We review almost 1000 papers using CMR modeling and find that almost 40% of studies fitting the searching criteria (N = 115) detected transients. Nevertheless, few researchers have considered the ecological or evolutionary meaning of the transient phenomenon. Only three studies from the reviewed papers considered transients to be a cost of first reproduction. We also analyze a long-term individual monitoring dataset (1988–2012) on a long-lived bird to quantify transients, and we use a life table response experiment (LTRE) to measure the consequences of transients at a population level. As expected, population growth rate decreased when the environment became harsher while the proportion of transients increased. LTRE analysis showed that population growth can be substantially affected by changes in traits that are variable under environmental stochasticity and deterministic perturbations, such as recruitment, fecundity of experienced individuals, and transient probabilities. This occurred even though sensitivities and elasticities of these parameters were much lower than those for adult survival. The proportion of transients also increased with the strength of density-dependence. These results have implications for ecological and evolutionary studies and may stimulate other researchers to explore the ecological processes behind the occurrence of transients in capture–recapture studies. In population models, the inclusion of a specific state for transients may help to make more reliable predictions for endangered and harvested species.

scholarly journals Reduced growth with increased quotas of particulate organic and inorganic carbon in the coccolithophore <i>Emiliania huxleyi</i> under future ocean climate change conditions

2020 ◽  
Author(s):  
Yong Zhang ◽  
Sinéad Collins ◽  
Kunshan Gao
Keyword(s):  
Growth Rate ◽  
Population Growth ◽  
Ocean Acidification ◽  
Population Growth Rate ◽  
Inorganic Carbon ◽  
Inorganic Nitrogen ◽  
Emiliania Huxleyi ◽  
Environmental Drivers ◽  
Nutrient Concentrations ◽  
Organic And Inorganic Carbon

Abstract. Effects of ocean acidification and warming on marine primary producers can be modulated by other environmental factors, such as levels of nutrients and light. Here, we investigated the interactive effects of five oceanic environmental drivers (CO2, temperature, light, dissolved inorganic nitrogen and phosphate) on growth rate, particulate organic (POC) and inorganic (PIC) carbon quotas of the cosmopolitan coccolithophore Emiliania huxleyi. Population growth rate increased with increasing temperature (16 to 20 °C) and light intensities (60 to 240 μmol photons m−2  s−1), but decreased with elevated pCO2 concentrations (370 to 960 μatm) and reduced availability of nitrate (24.3 to 7.8 μmol L−1) and phosphate (1.5 to 0.5 μmol L−1). POC quotas were predominantly enhanced by combined effects of increased pCO2 and decreased availability of phosphate. PIC quotas increased with decreased availability of nitrate and phosphate. Our results show that concurrent changes in nutrient concentrations and pCO2 levels predominantly affected growth, photosynthetic carbon fixation and calcification of E. huxleyi, and imply that plastic responses to progressive ocean acidification, warming and decreasing availability of nitrate and phosphate reduce population growth rate while increasing cellular quotas of particulate organic and inorganic carbon of E. huxleyi, ultimately affecting coccolithophore-related ecological and biogeochemical processes.

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 Full life-cycle models from ring-recovery data: estimating fecundity from age ratios at capture

2018 ◽  
Author(s):  
Todd. W. Arnold
Keyword(s):  
Growth Rate ◽  
Life Cycle ◽  
Population Growth ◽  
Population Growth Rate ◽  
Large Scale ◽  
Adult Survival ◽  
List Type ◽  
Vital Rates ◽  
Full Life Cycle ◽  
Full Life

AbstractTag-recovery data from organisms captured and marked post breeding are commonly used to estimate juvenile and adult survival. If annual fecundity could also be estimated, tagging studies such as European and North American bird-ringing schemes could provide all parameters needed for building full life-cycle projection models.I modified existing tag-recovery models to allow estimation of annual fecundity using age composition and recapture probabilities obtained during routine banding operations of northern pintails (Anas acuta) and dark-eyed juncos (Junco hyemalis), and I conducted simulations to assess estimator performance in relation to sample size.For pintails, population growth rate from band-recovery data (λ = 0.929, SD 0.060) was similar but less precise than count-based estimates from the Waterfowl Breeding Pair and Habitat Survey (λ 0.945, SE 0.001). Models with temporal variation in vital rates indicated that annual population growth in pintails was driven primarily by variation in fecundity. Juncos had lower survival but greater fecundity, and their estimated population growth rate (λ 1.01, SD 0.19) was consistent with count-based surveys (λ 0.986).Simulations indicated that reliable (CV < 0.10) estimates of fecundity could be obtained with >1000 same-season live encounters. Although precision of survival estimates depended primarily on numbers of adult recoveries, estimates of population growth rate were most sensitive to total number of live encounters.Synthesis and applications: Large-scale ring-recovery programmes could be used to estimate annual fecundity in many species of birds, but the approach requires better data curation, including accurate assessment of age, better reporting of banding totals and greater emphasis on obtaining and reporting same-season live encounters.

scholarly journals Reduced growth with increased quotas of particulate organic and inorganic carbon in the coccolithophore <i>Emiliania huxleyi</i> under future ocean climate change conditions

2020 ◽  
Vol 17 (24) ◽  
pp. 6357-6375
Author(s):  
Yong Zhang ◽  
Sinéad Collins ◽  
Kunshan Gao
Keyword(s):  
Growth Rate ◽  
Population Growth ◽  
Ocean Acidification ◽  
Population Growth Rate ◽  
Inorganic Carbon ◽  
Inorganic Nitrogen ◽  
Emiliania Huxleyi ◽  
Environmental Drivers ◽  
Nutrient Concentrations ◽  
Organic And Inorganic Carbon

Abstract. Effects of ocean acidification and warming on marine primary producers can be modulated by other environmental factors, such as levels of nutrients and light. Here, we investigated the interactive effects of five oceanic environmental drivers (CO2, temperature, light, dissolved inorganic nitrogen and phosphate) on the growth rate, particulate organic carbon (POC) and particulate inorganic carbon (PIC) quotas of the cosmopolitan coccolithophore Emiliania huxleyi. The population growth rate increased with increasing temperature (16 to 20 ∘C) and light intensities (60 to 240 µmolphotonsm-2s-1) but decreased with elevated pCO2 concentrations (370 to 960 µatm) and reduced availability of nitrate (24.3 to 7.8 µmol L−1) and phosphate (1.5 to 0.5 µmol L−1). POC quotas were predominantly enhanced by the combined effects of increased pCO2 and decreased availability of phosphate. PIC quotas increased with decreased availability of nitrate and phosphate. Our results show that concurrent changes in nutrient concentrations and pCO2 levels predominantly affected the growth, photosynthetic carbon fixation and calcification of E. huxleyi and imply that plastic responses to progressive ocean acidification, warming, and decreasing availability of nitrate and phosphate reduce the population growth rate while increasing cellular quotas of particulate organic and inorganic carbon of E. huxleyi, ultimately affecting coccolithophore-related ecological and biogeochemical processes.

scholarly journals Biological scaling in green algae: the role of cell size and geometry

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Helena Bestová ◽  
Jules Segrestin ◽  
Klaus von Schwartzenberg ◽  
Pavel Škaloud ◽  
Thomas Lenormand ◽  
...  
Keyword(s):  
Growth Rate ◽  
Population Growth ◽  
Population Growth Rate ◽  
Internal Diffusion ◽  
Scaling Exponent ◽  
Power Scaling ◽  
Nutrient Distribution ◽  
Metabolic Scaling ◽  
Key Factor ◽  
Size And Morphology

AbstractThe Metabolic Scaling Theory (MST), hypothesizes limitations of resource-transport networks in organisms and predicts their optimization into fractal-like structures. As a result, the relationship between population growth rate and body size should follow a cross-species universal quarter-power scaling. However, the universality of metabolic scaling has been challenged, particularly across transitions from bacteria to protists to multicellulars. The population growth rate of unicellulars should be constrained by external diffusion, ruling nutrient uptake, and internal diffusion, operating nutrient distribution. Both constraints intensify with increasing size possibly leading to shifting in the scaling exponent. We focused on unicellular algae Micrasterias. Large size and fractal-like morphology make this species a transitional group between unicellular and multicellular organisms in the evolution of allometry. We tested MST predictions using measurements of growth rate, size, and morphology-related traits. We showed that growth scaling of Micrasterias follows MST predictions, reflecting constraints by internal diffusion transport. Cell fractality and density decrease led to a proportional increase in surface area with body mass relaxing external constraints. Complex allometric optimization enables to maintain quarter-power scaling of population growth rate even with a large unicellular plan. Overall, our findings support fractality as a key factor in the evolution of biological scaling.

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