The Relative 'Importance' of Life-History Stages to Population Growth: Prospective and Retrospective Analyses

Horvitz, Carol C.; Schemske, Douglas W.; Caswell, Hal

doi:10.21236/ada330618

Cited by 94 publications

(166 citation statements)

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“…We used a two-way life table response experiment (LTRE) with sheep density treatment and year as fixed effects to quantify the contribution of different matrix elements to the differences in k between populations and years (Horvitz et al 1997;Caswell 2001). To investigate if some life history components contributed consistently to the variation in k between years, we calculated Pearson's correlation coefficients between LTRE contributions to the year effect and deviations of k from k of the overall mean matrix.…”

Section: Statistical Analyses and Transition Matrix Modellingmentioning

confidence: 99%

Interactions between local climate and grazing determine the population dynamics of the small herb Viola biflora

et al. 2010

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Plants of low stature may benefit from the presence of large herbivores through removal of tall competitive neighbours and increased light availability. Accordingly, removal of grazers has been predicted to disfavour small species. In addition to this indirect beneficial effect, the population dynamics of plants is strongly influenced by variation in external conditions such as temperature and precipitation. However, few studies have examined the interaction between large herbivores and inter-annual variation in climate for the population dynamics of small plant species not preferred by herbivores. We studied three populations of the perennial herb Viola biflora exposed to different sheep densities (high, low and zero) for 6 years in a field experiment. Plants were also impacted by invertebrate and small vertebrate herbivores (rodents). Rates of growth were marginally higher at high sheep densities, and during warm summers both survival and growth were higher when sheep were present. Thus, while the height of tall herbs was positively related to July temperature, it was less so in the treatments with sheep, suggesting that sheep reduce the negative effects of interspecific competition for this small herb. Life table response experiment analyses revealed that the population growth rate (k) was slightly lower in the absence of sheep, but between-year variation in k was larger than variation among sheep density treatments. k was negatively related to July temperature, with an additional negative effect of vertebrate grazing frequency (sheep or rodent grazing). The evidence from this 6-year study suggests that the population dynamics of Viola biflora is determined by a complex interplay between climate and grazing by both large and small herbivores.

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Section: Statistical Analyses and Transition Matrix Modellingmentioning

confidence: 99%

Interactions between local climate and grazing determine the population dynamics of the small herb Viola biflora

et al. 2010

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“…Elasticities can be used for comparison of life history strategies within and among taxa (de Kroon et al 2000) and for assessing the relative contribution of fitness components to variation in k (van Tienderen 1995; Horvitz et al 1997). We used the acronym ''k PM '' to identify the estimate of k using the projection matrix.…”

Section: Contributions Of Demographic Parameters To K and Variabilitymentioning

confidence: 99%

“…We did not have an estimate of juvenile survival so we used an estimate from a study of California We assessed the sensitivity of k to individual fitness components by calculating the elasticityê ð Þ of model parameters (Benton and Grant 1996;Caswell 2001). The relative sensitivity ofk PM to variation in fitness components (i.e., R, u, and juvenile survival) depends on both theê and the temporal variation of the fitness components (Horvitz et al 1997;Gaillard et al 2000). For example, u may have high elasticity but have less importance in determining annual changes in k than components with lower elasticity yet greater temporal variability.…”

Section: Contributions Of Demographic Parameters To K and Variabilitymentioning

confidence: 99%

Sources of variability in spotted owl population growth rate: testing predictions using long-term mark–recapture data

Seamans

Gutiérrez

2006

Oecologia

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For long-lived iteroparous vertebrates that annually produce few young, life history theory predicts that reproductive output (R) and juvenile survival should influence temporal variation in population growth rate (lambda) more than adult survival does. We examined this general prediction using 15 years of mark-recapture data from a population of California spotted owls (Strix occidentalis occidentalis). We found that survival of individuals > or =1 year old (phi) exhibited much less temporal variability (CV = 0.04), where CV is coefficient of variation, than R (CV = 0.83) and that R was strongly influenced by environmental stochasticity. Although lambda was most sensitive (ê; log-transformed sensitivity) to phi (ê = 0.77), and much less sensitive to either R (ê = 0.12) or juvenile survival (survival rate of owls from fledging to 1 year old; ê = 0.12), we estimated that R contributed as much as phi to the observed annual variability in lambda. The contribution of juvenile survival to variability in lambda was proportional to its ê. These results are consistent with the hypothesis that natural selection may have favored the evolution of longevity in spotted owls as a strategy to increase the probability of experiencing favorable years for reproduction. Our finding that annual weather patterns that most affected R (temperature and precipitation during incubation) and phi (conditions during winter related to the Southern Oscillation Index) were equally good at explaining temporal variability in lambda supports the conclusion that R and phi were equally responsible for variability in lambda. Although currently accepted conservation measures for spotted owl populations attempt to enhance survival, our results indicated that conservation measures that target R may be as successful, as long as actions do not reduce phi.

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“…One may think that the low contribution of fecundity to the variation in k is expected in perennial plants whose demography is predicted to be less sensitive to changes in fecundity by sensitivity and elasticity analysis (Silvertown et al 1996;Franco and Silvertown 2004). However, the relative contribution of fecundity depends not only on the pattern of sensitivity but also on that of variability of demographic rates (Horvitz et al 1997;Caswell 2000), and recent studies using retrospective LTRE analysis gave variable results among perennials. In an understory herb Heliconia acuminata, reduced k in small experimentally fragmented forests compared to continuous forests was attributable to reduction both in fecundity and in plant growth (Bruna and Oli 2005), while in a rare monocarpic herb Centaurea corymbosa, Fréville et al (2004) found a predominant effect of fecundity on spatial and temporal (Bruna 2002;Aguilar et al 2006), and frequently suggested that these changes threaten the persistence of populations (Jennersten 1988;Kéry et al 2000).…”

Section: Discussionmentioning

confidence: 99%

“…Whereas the lack of sufficient data tends to result in substituting spatial variation for temporal variation in demographic models (e.g., Silva et al 1991), we do not generally know whether plant demography responds similarly to these two types of environmental variability (Horvitz et al 1997;Jongejans and de Kroon 2005). A better understanding will probably come from studies that investigate long-term dynamics of multiple populations by analyzing both temporal and spatial variations in demography.…”

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confidence: 99%

Demographic response of plant populations to habitat fragmentation and temporal environmental variability

Tomimatsu

Ohara

2009

Oecologia

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Many plant species currently exist in fragmented populations of different sizes, while they also experience unpredictable climatic fluctuation over time. However, we still understand little about how plant demography responds to such spatial and temporal environmental variability. We studied population dynamics of an understory perennial herb Trillium camschatcense in the Tokachi plain of Hokkaido, Japan, where a significant effect of forest fragmentation on seedling recruitment was previously reported. Four populations across a range of fragment sizes were studied for 6 years, and the data were analyzed using matrix population models. Per capita fecundity (the number of recruits per plant) varied greatly among populations, but the variation in population growth rates (lambda) was mainly driven by the variation in stasis and growth rates, suggesting that the general trend of reduced fecundity in fragmented populations may not be readily translated into subsequent dynamics. Temporal variation in lambda among years was more than 2 times larger than spatial variation among populations, and this result was likely attributable to the contrasting response of correlation structures among demographic rates. The among-population variation in lambda was dampened by negative covariation between matrix elements possibly due to density-dependent regulation as well as an inherent constraint that some elements are not independent, whereas positive covariation between matrix elements resulted in large temporal variation in lambda. Our results show that population dynamics responded differently to habitat fragmentation and temporal variability of the environment, emphasizing the need to discriminate these spatial and temporal variations in demographic models. Although no populations were projected to be declining in stochastic simulations, correlation between current habitat size and plant density implies historical lambda is positively related to habitat size.

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The Relative 'Importance' of Life-History Stages to Population Growth: Prospective and Retrospective Analyses

Cited by 94 publications

References 0 publications

Interactions between local climate and grazing determine the population dynamics of the small herb Viola biflora

Interactions between local climate and grazing determine the population dynamics of the small herb Viola biflora

Sources of variability in spotted owl population growth rate: testing predictions using long-term mark–recapture data

Demographic response of plant populations to habitat fragmentation and temporal environmental variability

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