Time‐lagged effects of weather on plant demography: drought and Astragalus scaphoides

Abstract

Abstract. Temperature and precipitation determine the conditions where plant species can occur. Despite their significance, to date, surprisingly few demographic field studies have considered the effects of abiotic drivers. This is problematic because anticipating the effect of global climate change on plant population viability requires understanding how weather variables affect population dynamics. One possible reason for omitting the effect of weather variables in demographic studies is the difficulty in detecting tight associations between vital rates and environmental drivers. In this paper, we applied Functional Linear Models (FLMs) to long-term demographic data of the perennial wildflower, Astragalus scaphoides, and explored sensitivity of the results to reduced amounts of data. We compared models of the effect of average temperature, total precipitation, or an integrated measure of drought intensity (standardized precipitation evapotranspiration index, SPEI), on plant vital rates. We found that transitions to flowering and recruitment in year t were highest if winter/spring of year t was wet (positive effect of SPEI). Counterintuitively, if the preceding spring of year t À 1 was wet, flowering probabilities were decreased (negative effect of SPEI). Survival of vegetative plants from t À 1 to t was also negatively affected by wet weather in the spring of year t À 1 and, for large plants, even wet weather in the spring of t À 2 had a negative effect. We assessed the integrated effect of all vital rates on life history performance by fitting FLMs to the asymptotic growth rate, log(k t ). Log(k t ) was highest if dry conditions in year t À 1 were followed by wet conditions in the year t. Overall, the positive effects of wet years exceeded their negative effects, suggesting that increasing frequency of drought conditions would reduce population viability of A. scaphoides. The drought signal weakened when reducing the number of monitoring years. Substituting space for time did not recover the weather signal, probably because the weather variables varied little between sites. We detected the SPEI signal when the analysis included data from two sites monitored over 20 yr (2 9 20 observations), but not when analyzing data from four sites monitored over 10 yr (4 9 10 observations).

Bumblebee worker body size affects new worker production in different resource environments

“…Previously, FLMs have been used to evaluate the lagged effects of environmental drivers on plant population dynamics (Teller et al . 2016; Tenhumberg et al . 2018).…”

“…To date, only two studies have reported applying functional smoothing approaches to high-dimensional ecological systems by exploring how lagged environmental drivers influence plant performance (Teller et al . 2016; Tenhumberg et al . 2018).…”

Using statistics to design and estimate vital rates in matrix population models for a perennial herb

“…To examine the effect of matrix structure on estimates of population parameters, we constructed 4 × 4 and 10 × 10 matrices based on the two previously published population models. The 4 × 4 matrix, based on expert opinion, is structurally identical to that previously used by Lesica () and Tenhumberg, Crone, Ramula, and Tyre () for this species, and consists of small vegetative plants (<6 leaves), large vegetative plants (≥6 leaves), flowering plants, and dormant plants. In this matrix, individuals from any stage category can enter the dormant category and vice versa (Figure a, Table S2 in Supporting Information).…”

Increasing temperature threatens an already endangered coastal dune plant

“…For example, for year 2012 (t=2012) we considered the climate anomaly observed between June 2011 and May 2012, and between June 2010 and May 2011 to predict the flowering probability and number of inflorescences observed in June 2012, and to predict the survival and growth occurred from June 2012 to June 2013. We thus tested for a lag in the effect of climatic drivers on plant vital rates (see also Teller et al 2016;Tenhumberg et al 2018).…”