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 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.

Diagnosing declining grassland wader populations using simple matrix models

2009 ◽  
Vol 59 (1) ◽  
pp. 127-144 ◽  
Author(s):  
Lia Hemerik ◽  
Chris Klok ◽  
Maja Roodbergen
Keyword(s):  
Growth Rate ◽  
Population Growth ◽  
Matrix Models ◽  
Population Growth Rate ◽  
Adult Stage ◽  
Demographic Data ◽  
Leslie Matrix ◽  
Adult Survival ◽  
Demographic Parameters ◽  
Survival And Reproduction

AbstractMany populations of wader species have shown a strong decline in number in Western-Europe in recent years. The use of simple population models such as matrix models can contribute to conserve these populations by identifying the most profitable management measures. Parameterization of such models is often hampered by the availability of demographic data (survival and reproduction). In particular, data on survival in the pre-adult (immature) stage of wader species that remain in wintering areas outside Europe are notoriously difficult to obtain, and are therefore virtually absent in the literature. To diagnose population decline in the wader species; Black-tailed Godwit, Curlew, Lapwing, Oystercatcher, and Redshank, we extended an existing modelling framework in which incomplete demographic data can be analysed, developed for species with a pre-adult stage of one year. The framework is based on a Leslie matrix model with three parameters: yearly reproduction (number of fledglings per pair), yearly pre-adult (immature) and yearly adult (mature) survival. The yearly population growth rate of these populations and the relative sensitivity of this rate to changes in survival and reproduction parameters (the elasticity) were calculated numerically and, if possible, analytically. The results showed a decrease in dependence on reproduction and an increase in pre-adult survival of the population growth rate with an increase in the duration of the pre-adult stage. In general, adult survival had the highest elasticity, but elasticity of pre-adult survival increased with time to first reproduction, a result not reported earlier. Model results showed that adult survival and reproduction estimates reported for populations of Redshank and Curlew were too low to maintain viable populations. Based on the elasticity patterns and the scope for increase in actual demographic parameters we inferred that conservation of the Redshank and both Curlew populations should focus on reproduction. For one Oystercatcher and the Black-tailed Godwit populations we suggested a focus on both reproduction and pre-adult survival. For the second Oystercatcher population pre-adult survival seemed the most promising target for conservation. And for the Lapwing populations all demographic parameters should be considered.

scholarly journals Fall supplemental feeding increases population growth rate of an endangered caribou herd

PeerJ ◽  
2021 ◽  
Vol 9 ◽  
pp. e10708
Author(s):  
Douglas C. Heard ◽  
Kathryn L. Zimmerman
Keyword(s):  
Growth Rate ◽  
Population Growth ◽  
Population Growth Rate ◽  
Population Increase ◽  
Adult Survival ◽  
Management Approach ◽  
Annual Growth Rate ◽  
Supplemental Feeding ◽  
Management Actions ◽  
The Impact

Most woodland caribou (Rangifer tarandus caribou) populations are declining primarily because of unsustainable predation resulting from habitat-mediated apparent competition. Wolf (Canis lupus) reduction is an effective recovery option because it addresses the direct effect of predation. We considered the possibility that the indirect effects of predation might also affect caribou population dynamics by adversely affecting summer foraging behaviour. If spring and/or summer nutrition was inadequate, then supplemental feeding in fall might compensate for that limitation and contribute to population growth. Improved nutrition and therefore body condition going into winter could increase adult survival and lead to improved reproductive success the next spring. To test that hypothesis, we fed high-quality food pellets to free-ranging caribou in the Kennedy Siding caribou herd each fall for six years, starting in 2014, to see if population growth rate increased. Beginning in winter 2015–16, the Province of British Columbia began a concurrent annual program to promote caribou population increase by attempting to remove most wolves within the Kennedy Siding and the adjacent caribou herds’ ranges. To evaluate the impact of feeding, we compared lambdas before and after feeding began, and to the population trend in the adjacent Quintette herd over the subsequent four years. Supplemental feeding appeared to have an incremental effect on population growth. Population growth of the Kennedy Siding herd was higher in the year after feeding began (λ = 1.06) compared to previous years (λ = 0.91) and to the untreated Quintette herd (λ = 0.95). Average annual growth rate of the Kennedy Siding herd over the subsequent four years, where both feeding and wolf reduction occurred concurrently, was higher than in the Quintette herd where the only management action in those years was wolf reduction (λ = 1.16 vs. λ = 1.08). The higher growth rate of the Kennedy Siding herd was due to higher female survival (96.2%/yr vs. 88.9%/yr). Many caribou were in relatively poor condition in the fall. Consumption of supplemental food probably improved their nutritional status which ultimately led to population growth. Further feeding experiments on other caribou herds using an adaptive management approach would verify the effect of feeding as a population recovery tool. Our results support the recommendation that multiple management actions should be implemented to improve recovery prospects for caribou.

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 Reef manta ray life history and demography: is it really all about survival?

2016 ◽  
Author(s):  
Isabel M Smallegange ◽  
Isabelle BC van der Ouderaa ◽  
Yara Tibiriçá
Keyword(s):  
Growth Rate ◽  
Survival Rate ◽  
Population Growth ◽  
Population Growth Rate ◽  
Survival Rates ◽  
Adult Survival ◽  
Lifetime Reproductive Success ◽  
Annual Survival ◽  
Manta Ray ◽  
Reef Manta Ray

Background. The trade in gill plates of devil and manta rays has increased greatly over the last two decades. The resulting increased mortality, in addition to mortality caused by by-catch, means that many ray populations are declining in size. The aim of this study was to ascertain the main demographic drivers of population change in reef manta rays (Manta alfredi) to increase our understanding of their demography and hence provide insight into potential conservation measures. Methods. We developed a population projection model for reef manta rays and used published life history data to parameterise the model and also used these data as points of reference to compare our model output to. Because little is known about yearling and juvenile survival of reef manta rays, we conducted our analyses across a range of plausible survival rate values of yearlings, juveniles, and also adults. Results. The model accurately captured observed patterns of variation in population growth rate, lifetime reproductive success and cohort generation time for different reef manta ray populations around the world. Varying the survival rates of the different life stages revealed that increasing adult annual survival rate always positively and additively affected population growth rate, lifetime reproductive success and cohort generation time. Variation in yearling and juvenile annual survival rate, however, had different and varying effects on the latter three population descriptors, highlighting the importance of obtaining accurate estimates of these survival rates from natural populations. Our elasticity analysis revealed that for both declining and stable populations, the population growth rate is most sensitive to changes in either juvenile or adult survival rate, depending on yearling and adult annual survival rate values. Discussion. Many reef manta ray populations are declining, resulting in local extinction unless effective conservation measures are taken. Based on our detailed demographic analysis, we suggest that reef manta ray conservation would particularly benefit from focusing on increasing juvenile and adult survival.

scholarly journals Density Dependence and Adult Survival Drive Dynamics in Two High Elevation Amphibian Populations

Diversity ◽  
2020 ◽  
Vol 12 (12) ◽  
pp. 478
Author(s):  
Amanda M. Kissel ◽  
Simone Tenan ◽  
Erin Muths
Keyword(s):  
Growth Rate ◽  
Population Growth ◽  
Density Dependence ◽  
Population Growth Rate ◽  
Geometric Mean ◽  
High Elevation ◽  
Amphibian Conservation ◽  
Adult Survival ◽  
Extrinsic Factors ◽  
Open Population

Amphibian conservation has progressed from the identification of declines to mitigation, but efforts are hampered by the lack of nuanced information about the effects of environmental characteristics and stressors on mechanistic processes of population regulation. Challenges include a paucity of long-term data and scant information about the relative roles of extrinsic (e.g., weather) and intrinsic (e.g., density dependence) factors. We used a Bayesian formulation of an open population capture-recapture model and >30 years of data to examine intrinsic and extrinsic factors regulating two adult boreal chorus frogs (Pseudacris maculata) populations. We modelled population growth rate and apparent survival directly, assessed their temporal variability, and derived estimates of recruitment. Populations were relatively stable (geometric mean population growth rate >1) and regulated by negative density dependence (i.e., higher population sizes reduced population growth rate). In the smaller population, density dependence also acted on adult survival. In the larger population, higher population growth was associated with warmer autumns. Survival estimates ranged from 0.30–0.87, per-capita recruitment was <1 in most years, and mean seniority probability was >0.50, suggesting adult survival is more important to population growth than recruitment. Our analysis indicates density dependence is a primary driver of population dynamics for P. maculata adults.

scholarly journals Reef manta ray life history and demography: is it really all about survival?

2016 ◽  
Author(s):  
Isabel M Smallegange ◽  
Isabelle BC van der Ouderaa ◽  
Yara Tibiriçá
Keyword(s):  
Growth Rate ◽  
Survival Rate ◽  
Population Growth ◽  
Population Growth Rate ◽  
Survival Rates ◽  
Adult Survival ◽  
Lifetime Reproductive Success ◽  
Annual Survival ◽  
Manta Ray ◽  
Reef Manta Ray

Background. The trade in gill plates of devil and manta rays has increased greatly over the last two decades. The resulting increased mortality, in addition to mortality caused by by-catch, means that many ray populations are declining in size. The aim of this study was to ascertain the main demographic drivers of population change in reef manta rays (Manta alfredi) to increase our understanding of their demography and hence provide insight into potential conservation measures. Methods. We developed a population projection model for reef manta rays and used published life history data to parameterise the model and also used these data as points of reference to compare our model output to. Because little is known about yearling and juvenile survival of reef manta rays, we conducted our analyses across a range of plausible survival rate values of yearlings, juveniles, and also adults. Results. The model accurately captured observed patterns of variation in population growth rate, lifetime reproductive success and cohort generation time for different reef manta ray populations around the world. Varying the survival rates of the different life stages revealed that increasing adult annual survival rate always positively and additively affected population growth rate, lifetime reproductive success and cohort generation time. Variation in yearling and juvenile annual survival rate, however, had different and varying effects on the latter three population descriptors, highlighting the importance of obtaining accurate estimates of these survival rates from natural populations. Our elasticity analysis revealed that for both declining and stable populations, the population growth rate is most sensitive to changes in either juvenile or adult survival rate, depending on yearling and adult annual survival rate values. Discussion. Many reef manta ray populations are declining, resulting in local extinction unless effective conservation measures are taken. Based on our detailed demographic analysis, we suggest that reef manta ray conservation would particularly benefit from focusing on increasing juvenile and adult survival.

Hierarchies of cause: understanding rarity in an endemic shrub Verticordia staminosa (Myrtaceae) with a highly restricted distribution

2007 ◽  
Vol 55 (3) ◽  
pp. 194 ◽  
Author(s):  
Colin J. Yates ◽  
Philip G. Ladd ◽  
David J. Coates ◽  
Shelley McArthur
Keyword(s):  
Growth Rate ◽  
Genetic Variation ◽  
Population Growth ◽  
Population Growth Rate ◽  
Seedling Recruitment ◽  
Population Viability ◽  
Stochastic Simulations ◽  
Early Pleistocene ◽  
Climatic Fluctuations ◽  
Restricted Distribution

Verticordia staminosa C.Gardner & A.C.George subsp. staminosa is an extremely rare shrub occurring as an isolated population of ~1200 plants on a granite outcrop in the semi-arid agricultural region of Western Australia, separated from its closest relative V. staminosa subsp. cylindracea by 400 km. We aimed to determine a hierarchy of causes for explaining the extremely restricted distribution of subsp. staminosa, and to determine the genetic relationships among populations within both subspecies. We measured allozyme variation in all known populations of the two subspecies. There were exceptionally high levels of genetic divergence between subsp. staminosa and subsp. cylindracea, including an apparent duplication of the gene encoding phosphoglucomutase, leading to an additional gene in subsp. cylindracea. These findings combined with UPGMA analysis indicate a very long period of historical separation, perhaps originating in the early Pleistocene. Genetic variation was partitioned mostly between rather than within populations, with very low levels of genetic variation within populations of both subspecies. For subsp. staminosa we quantified seed production for three consecutive years and demography for five consecutive years. We used transition matrix models to describe the shrub’s population dynamics and stochastic simulations to explicitly compare the effects of low rainfall and disturbance on population viability. Verticordia staminosa subsp. staminosa produces large numbers of seeds each year and has flower to fruit ratios greater than reported for related rare and common congeners. Seedling recruitment occurs in most years, with pulses in the wettest years. The mean finite population growth rate was 1.031. Elasticity analyses showed that population growth rate was more sensitive to stasis of established plants than to seedling recruitment. Population viability declined with lower rainfall and increased fire-related mortality of adult plants. Rarity in subsp. staminosa is best explained by evolutionary history and the interaction of climate change and disturbances such as fire that kill plants. Climatic fluctuations since the late Pliocene might have led to stochastic extinction episodes of populations on other granite outcrops, resulting in the currently restricted distribution. We discuss the implications of our findings for management of the species.

scholarly journals Adult survival and population growth rate in Colorado big brown bats (Eptesicus fuscus)

2011 ◽  
Vol 92 (2) ◽  
pp. 433-443 ◽  
Author(s):  
Thomas J. O'Shea ◽  
Laura E. Ellison ◽  
Thomas R. Stanley
Keyword(s):  
Growth Rate ◽  
Population Growth ◽  
Population Growth Rate ◽  
Eptesicus Fuscus ◽  
Adult Survival ◽  
Big Brown Bats
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