Consequences of heterogeneity in survival probability in a population of Florida scrub‐jays

Fox, Gordon A.; Kendall, Bruce E.; Fitzpatrick, John W.; Woolfenden, Glen E.

doi:10.1111/j.1365-2656.2006.01110.x

Cited by 49 publications

(56 citation statements)

References 37 publications

(55 reference statements)

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“…As such, it can be easily integrated with models of environmental stochasticity and demographic heterogeneity, as has already been done for survival (e.g., Kendall 1998;Fox et al 2006), facilitating the rigorous development of integrated models (Melbourne and Hastings 2008). The model can also be integrated with recent advances in life-history dynamics (Tuljapurkar et al 2009) to more rigorously evaluate how patterns of variation in reproductive success affect evolutionary demography.…”

Section: Discussionmentioning

confidence: 99%

A Stochastic Model for Annual Reproductive Success

Kendall

Wittmann

2010

The American Naturalist

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Demographic stochasticity can have large effects on the dynamics of small populations as well as on the persistence of rare genotypes and lineages. Survival is sensibly modeled as a binomial process, but annual reproductive success (ARS) is more complex and general models for demographic stochasticity do not exist. Here we introduce a stochastic model framework for ARS and illustrate some of its properties. We model a sequence of stochastic events: nest completion, the number of eggs or neonates produced, nest predation, and the survival of individual offspring to independence. We also allow multiple nesting attempts within a breeding season. Most of these components can be described by Bernoulli or binomial processes; the exception is the distribution of offspring number. Using clutch and litter size distributions from 53 vertebrate species, we demonstrate that among-individual variability in offspring number can usually be described by the generalized Poisson distribution. Our model framework allows the demographic variance to be calculated from underlying biological processes and can easily be linked to models of environmental stochasticity or selection because of its parametric structure. In addition, it reveals that the distributions of ARS are often multimodal and skewed, with implications for extinction risk and evolution in small populations.

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Section: Discussionmentioning

confidence: 99%

A Stochastic Model for Annual Reproductive Success

Kendall

Wittmann

2010

The American Naturalist

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“…More than a theoretical curiosity, cohort selection has been rigorously demonstrated in experimental laboratory populations (Manton et al 1981, Carey et al 1992, Vaupel and Carey 1993. The underlying frailty heterogeneity has been documented in a variety of species, including crocodiles (Isberg et al 2006), baboons (Bronikowski et al 2002), birds (Wintrebert et al 2005, Fox et al 2006, wild plants (Beckage andClark 2003, Landis et al 2005), domestic animals (Ducrocq et al 2000, Casellas et al 2004, humans (Yashin et al 1999, Garibotti et al 2006, and British aristocrats (Doblhammer and Oeppen 2003).…”

Section: Introductionmentioning

confidence: 99%

“…Another reason to think so is that a number of common processes can generate persistent heterogeneity in both frailty and reproduction among individuals in a cohort. These include fine-scale spatial habitat heterogeneity (e.g., Gates and Gysel 1978, Boulding and Van Alstyne 1993, Menge et al 1994, Winter et al 2000, Franklin et al 2000 Bollinger andGavin 2004, Landis et al 2005), unequal allocation of parental care (e.g., Manser andAvey 2000, Johnstone 2004), maternal family effect (e.g., Fox et al 2006), conditions during early development, including birth order effects (e.g., Lindstro¨m 1999), persistent social rank (e.g., von Holst et al 2002), and genetics (e.g., Yashin et al 1999, Ducrocq et al 2000, Gerdes et al 2000, Casellas et al 2004, Isberg et al 2006. Thus, we would expect cohort selection to be quite common in nature.…”

Section: Introductionmentioning

confidence: 99%

Demographic heterogeneity, cohort selection, and population growth

Kendall

Fox

Fujiwara

et al. 2011

Ecology

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129

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Abstract. Demographic heterogeneity-variation among individuals in survival and reproduction-is ubiquitous in natural populations. Structured population models address heterogeneity due to age, size, or major developmental stages. However, other important sources of demographic heterogeneity, such as genetic variation, spatial heterogeneity in the environment, maternal effects, and differential exposure to stressors, are often not easily measured and hence are modeled as stochasticity. Recent research has elucidated the role of demographic heterogeneity in changing the magnitude of demographic stochasticity in small populations. Here we demonstrate a previously unrecognized effect: heterogeneous survival in long-lived species can increase the long-term growth rate in populations of any size. We illustrate this result using simple models in which each individual's annual survival rate is independent of age but survival may differ among individuals within a cohort. Similar models, but with nonoverlapping generations, have been extensively studied by demographers, who showed that, because the more ''frail'' individuals are more likely to die at a young age, the average survival rate of the cohort increases with age. Within ecology and evolution, this phenomenon of ''cohort selection'' is increasingly appreciated as a confounding factor in studies of senescence. We show that, when placed in a population model with overlapping generations, this heterogeneity also causes the asymptotic population growth rate k to increase, relative to a homogeneous population with the same mean survival rate at birth. The increase occurs because, even integrating over all the cohorts in the population, the population becomes increasingly dominated by the more robust individuals. The growth rate increases monotonically with the variance in survival rates, and the effect can be substantial, easily doubling the growth rate of slow-growing populations. Correlations between parent and offspring phenotype change the magnitude of the increase in k, but the increase occurs even for negative parent-offspring correlations. The effect of heterogeneity in reproductive rate on k is quite different: growth rate increases with reproductive heterogeneity for positive parentoffspring correlation but decreases for negative parent-offspring correlation. These effects of demographic heterogeneity on k have important implications for population dynamics, population viability analysis, and evolution.

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“…With 35 years of data on the survival rates of a Florida scrub-jay population, one study found that at least 10 years of data were needed to estimate the parameters representing how family and age affect survival (Fox et al 2006). A simulation study found that stochastic population growth rates remained imprecise even with 11 years of data (Fieberg and Ellner 2001).…”

Section: Effects Of Dataset Lengthmentioning

confidence: 99%

“…Although data availability is a wellrecognized limitation to demographic studies, few studies have examined how many years of data would be sufficient (Fieberg andEllner 2001, Doak et al 2005), especially for long-lived species (but see Fox et al 2006). Encouragingly, a demographic model based on a three-year dataset accurately predicted the observed population growth, generation time, and net reproductive rate for the long-lived monocarp Campanula thyrsoides (Kuss et al 2008).…”

Section: Introductionmentioning

confidence: 99%

The effects of dataset length and mast seeding on the demography ofFrasera speciosa, a long-lived monocarpic plant

Che‐Castaldo

Inouye

2011

Ecosphere

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Citation: Che-Castaldo, J. P., and D. W. Inouye. 2011. The effects of dataset length and mast seeding on the demography of Frasera speciosa, a long-lived monocarpic plant. Ecosphere 2(11):126. doi:10.1890/ES11-00263.1Abstract. Frasera speciosa (Gentianaceae) is a long-lived monocarpic plant with mast seeding, a type of plant whose demography is rarely studied. Using a 35-year dataset from an ongoing study, we described the population dynamics of F. speciosa using matrix projection models, addressed how many years of data are needed to estimate population growth and elasticity values consistently, and examined the effects of mast seeding on demographic parameter estimates. Our results indicated that our population is likely stable, with the annual population growth rate near one (k ¼ 0.969, k s ¼ 0.967 with 95% CI ¼ 0.923-1.013). Mean generation time was 40 years and the mean estimated lifespan was 6.86 years with a high variance of 181.8 years for individuals starting in the seedling stage, consistent with observations of very long-lived individuals in the field. Elasticity values were highest for the transitions representing stasis and lowest for reproduction. For dataset length, 15 years of data yielded lambda estimates that were within 1% of the long-term estimate, but 20 years of data were needed to yield lambdas with confidence intervals that consistently overlap one. Although mast seeding is generally defined using the inter-annual variation in seed production per unit area, stochastic lambdas were not correlated with this measure of reproduction but instead correlated with per capita dormant seed production and per capita recruit production. Mean survival rate was also positively correlated with stochastic lambda estimates, despite the necessary increase in mortality in years with high reproduction. Our results indicated that the demography of F. speciosa is similar to that of other long-lived monocarps without mast seeding, that long datasets may be needed to capture the variation in demographic rates even for stable populations, and that life history stages with low elasticity values can still be very important to population growth.

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Consequences of heterogeneity in survival probability in a population of Florida scrub‐jays

Cited by 49 publications

References 37 publications

A Stochastic Model for Annual Reproductive Success

A Stochastic Model for Annual Reproductive Success

Demographic heterogeneity, cohort selection, and population growth

The effects of dataset length and mast seeding on the demography ofFrasera speciosa, a long-lived monocarpic plant

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