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opencc-zeroDec 2017View details →

Data from: Reproductive skipping as an optimal life history strategy in the southern elephant seal, Mirounga leonina

Intermittent breeding by which organisms skip some current reproductive opportunities in order to enhance future reproductive success is a common life history tradeoff among long-lived, iteroparous species. The southern elephant seal Mirounga leonina engages in intermediate breeding when body condition is low. While it is anticipated that this strategy may increase the lifetime reproductive output of this species, the conditions under which reproductive skipping are predicted to occur are not clear. Here I develop a dynamic state variable model based on published data that examines when southern elephant seals are predicted to optimally skip reproduction in order to maximize lifetime reproductive output as a function of current body mass, maternal age, and survivorship. I demonstrate that the optimal reproductive strategy for this species can include reproductive skipping, and that the conditions where this is optimal depend on patterns of mass-dependent adult female survival. I further show that intermittent breeding can increase lifetime reproductive output, and that the magnitude of this benefit increases with the ability of individual animals to replenish depleted body mass through foraging. Finally, I show that when the environment is variable and foraging is reduced in bad years, the benefit of adopting an optimal strategy that includes reproductive skipping increases asymptotically with the frequency of bad years. These results highlight the importance of characterizing the pattern of adult survival in this species, as well as the need to identify other factors that may influence the prevalence and benefits of reproductive skipping.

Figure 5 in Analysis of shape variability and life history strategies of Illex argentinus in the northern extreme of species distribution as a tool to differentiate spawning groups

Figure 5. Scatterplot of the relationship of PC1 on body weight separated by group (a), on body weight separated by sex (b), OvWBW (c) and NgWBW (d) for females separated by group.

Figure 3 in Analysis of shape variability and life history strategies of Illex argentinus in the northern extreme of species distribution as a tool to differentiate spawning groups

Figure 3. Schematic representation of the series of growth increments (GINC) read over the dorsal surface of the gladius, the filtering process and the back-calculation of the gladius growth.

Figure 1 in Analysis of shape variability and life history strategies of Illex argentinus in the northern extreme of species distribution as a tool to differentiate spawning groups

Figure 1. Spatial representation of the study area. (a–c) Positions of the samples of Illex argentinus collected from trawlers south-southeast of Brazil between 22° and 33°S and 45 and 722 m depth from 2001 to 2013. (b) Samples used in geometric morphometric analysis. (c) Samples used in traditional morphometric analysis. (d) Samples collected during a research cruise during August of 2004 in the same area to identify size-selective processes. Lines in maps represent 100, 300 and 700 m depth.

Figure 4 in Analysis of shape variability and life history strategies of Illex argentinus in the northern extreme of species distribution as a tool to differentiate spawning groups

Figure 4. Length distributions of the (a) Local Group (LG) and the (b) Migratory Group (MG) captured south-southeast of Brazil between 2009 and 2013. Scatterplots of the first (PC1) and second (PC2) components of the principal component analysis using body landmarks separated by group (c) and by sex (d). Scatterplot of relationship of PC1 on centroid size separated by group (e) and by sex (f).

Figure 2 in Analysis of shape variability and life history strategies of Illex argentinus in the northern extreme of species distribution as a tool to differentiate spawning groups

Figure 2. Landmark configuration on the body of Illex argentinus. Dashed line represents the longitudinal axis of the body.

Figure 8 in Analysis of shape variability and life history strategies of Illex argentinus in the northern extreme of species distribution as a tool to differentiate spawning groups

Figure 8. Length distributions of Illex argentinus captured in south-southeastern Brazil between 22° and 33°S and 45 and 722 m depth from 2001 to 2013.

Figure 7 in Analysis of shape variability and life history strategies of Illex argentinus in the northern extreme of species distribution as a tool to differentiate spawning groups

Figure 7. (a) Mean gladius length (GL) in research cruise, and (b) mean individuals recent growth trajectories of squid captured in research cruise reconstructed from gladius.

Figure 10 in Analysis of shape variability and life history strategies of Illex argentinus in the northern extreme of species distribution as a tool to differentiate spawning groups

Figure 10. Size differentiation of squid groups during the period of growth reconstructed expressed by the variation of the coefficient of asymmetry (g1) of the length frequency distributions by growth interval (days).

Figure 9 in Analysis of shape variability and life history strategies of Illex argentinus in the northern extreme of species distribution as a tool to differentiate spawning groups

Figure 9. Gladius length frequency distributions of Illex argentinus reconstructed for the last 15 days before the capture from the measured increments on the gladius for the trawls 2–4 (T2-4) and trawls 9–14 (T9-14) of the research cruise.

Figure 6 in Analysis of shape variability and life history strategies of Illex argentinus in the northern extreme of species distribution as a tool to differentiate spawning groups

Figure 6. Barplots represents the length distributions of males and females of Illex argentinus captured during the fourth trimester of 2006 south-southeast of Brazil and a sample from the Uruguayan/Argentine common fishing zone collected in 2005, here defined as pre-migratory group (J). The analysis aimed to verify a possible correspondence between J and the expected MG, represented by two samples collected in the south (S) and central (C) portions of the studied area and if J is morphometrically different from the LG, captured in the north (N) portion of study area (Figure 1(c)). Plots represent the principal component analysis of the samples N, C, S and J. FRAL, length of the fourth right arm; BW, body weight; MW, mantle weight; MP, mantle perimeter.

opencc-zeroOct 2022View details →

Life history strategy and extinction risk in the warm desert perennial spring ephemeral Astragalus holmgreniorum (Fabaceae)

This study of Astragalus holmgreniorum examines its adaptations to the warm desert environment and whether these adaptations will enable it to persist. Its spring ephemeral hemicryptophyte life history strategy is unusual in warm deserts. We used data from a 22-year demographic study supplemented with reproductive output, seed bank and germinant survival studies to examine the population dynamics of this species using discrete-time stochastic matrix modeling. The model showed that A. holmgreniorum is likely to persist in the warm desert in spite of high dormant-season mortality. It relies on a stochastically varying environment with high inter-annual variation in precipitation for persistence, but without a long-lived seed bank, environmental stochasticity confers no advantage. Episodic high reproductive output and frequent seedling recruitment along with a persistent seed bank are adaptations that facilitate its survival. These adaptations place its life history strategy further along the spectrum from 'slower' to 'faster' relative to other perennial spring ephemerals. Extinction risk for small populations is relatively high even though mean λs >1 because of high variance in year quality. This risk is also strongly dependent on seed bank starting values, creating a moving window of extinction risk that varies with population size through time. Astragalus holmgreniorum life history strategy combines the perennial spring ephemeral life form with features more characteristic of desert annuals. These adaptations permit persistence in the warm desert environment. A promising conclusion is that new populations of this endangered species can likely be established through direct seeding.

opencc-zeroNov 2022View details →

Demographic changes and life-history strategies predict the genetic diversity in crabs

Uncovering what predicts genetic diversity (GD) within species can help us access the status of populations and their evolutionary potential. Traits related to effective population size show a proportional association to GD, but evidence supports life-history strategies and habitat as the drivers of GD variation. Instead of investigating highly divergent taxa, focusing on one group could help to elucidate the factors influencing the GD. Additionally, most empirical data is based on vertebrate taxa; therefore, we might be missing novel patterns of GD found in neglected invertebrate groups. Here, we investigated the predictors of the GD in crabs (Brachyura) by compiling the most comprehensive cytochrome c oxidase subunit I (COI) available. Eight predictor variables were analyzed across 150 species (16,992 sequences) using linear models (multiple linear regression) and comparative methods (PGLS). Our results indicate that population size fluctuation represents the most critical trait predicting GD, with species that have undergone bottlenecks followed by population expansion showing lower GD. Egg size, pelagic larval duration, and habitat might play a role probably because of their association with how species respond to disturbances. Ultimately, K-strategists that have undergone bottlenecks are the species showing lower GD. Some variables do not show an association with GD as expected, most likely due to the taxon-specific role of some predictors, which should be considered in further investigations and generalizations. This work highlights the complexity underlying the predictors of GD and adds results from a marine invertebrate group to the current understanding of this topic.

opencc-by-4.0Nov 2022View details →

Why we cannot always expect life history strategies to directly inform on population sensitivity to environmental change

This repository contains information accompanying the manuscript  "Why we cannot always expect life history strategies to directly inform on sensitivity to environmental change" Rademaker et al. (2022, in progress).   The repository consists of a zip-file containing code and data to run the phylogenetic PCA, and a zip-file containing Matlab code to run the DEB-IPM population models.