Dispersal and demography contributions to population spread of Carduus nutans in its native and invaded ranges

Abstract

Summary 1.Invasive species usually exhibit different spatial population dynamics in their native and invaded range. This is often attributed to demographic differences, but may be due to differences in dispersal as well. 2. Regardless of how these dispersal and demographic differences from the native range arose, studying how they contributed to increases in population spread rates will increase our understanding of what has made these species invasive. Here we investigate which vital rates and dispersal parameters of the invasive thistle Carduus nutans drive the increases in spread rate in different invaded ranges compared to that in the native range in Eurasia. 3. We construct and analyse spatial integrodifference models that combine structured, local population models with mechanistic (WALD) models of seed dispersal by wind across a homogeneous landscape. Published and new demographic and dispersal data for single populations from the native (France) and invaded (Australia, New Zealand, Kansas and Pennsylvania) ranges were used for the parameterization. 4. We developed a variance decomposition method ( c *-LTRE) to analyse the contributions of the changes in the vital rates and dispersal parameters to the increases in the invasion wave speed ( c *) estimates for the different invaded ranges compared to that for the native range. 5. The c *-LTRE analysis showed that the net contribution of the dispersal parameters to c * increases varied among the populations from 51% (Australia), to 79% (Kansas), to 80% (New Zealand) and to 85% (Pennsylvanian experiment). Escape from natural enemies that reduce seed set by floral herbivory was important in all invaded ranges. Large positive contributions were also made by increases in rapid growth of seedlings and small rosettes, increases in flowering probabilities and potential seed production, as well as by increased plant height and lower falling velocities of the plumed seeds. 6. Synthesis . By incorporating a mechanistic dispersal model with a structured population model, and by linking this joint model to field data from several continents, we demonstrate the relative importance of dispersal and demography to invasion success. This approach can be used to analyse which aspects of an invader's life history have changed most importantly from the native range.Key-words: fixed-factor life table response experiment (LTRE), integrodifference equations, matrix population models, musk or nodding thistle, native vs. invaded range, plant height, seed terminal velocity, vital rates, Wald analytical long-distance model, wind speed

Seed terminal velocity, wind turbulence, and demography drive the spread of an invasive tree in an analytical model

“…For simplicity, j has previously been considered a constant equal to the Von Ka´rma´n constant (j ¼ 0.4; e.g., Skarpaas and Shea 2007, Jongejans et al 2008, Nathan et al 2011). Yet, j actually varies as a function of canopy density.…”

“…New models of spread have incorporated LDD with demography (Jongejans et al 2008, Soons and Bullock 2008, Thompson and Katul 2008, Nathan et al 2011. However, the importance of individual mechanistic dispersal parameters on population spread has been mostly assessed by simulation approaches (Jongejans et al 2008, Thompson and Katul 2008, Coutts et al 2011, Nathan et al 2011. Indeed, a limitation in the use of integrodifference equation models for perturbation analysis of spread rate is the need to describe dispersal with a function for which a moment-generating function is known.…”

“…It is a simplification of the coupled Eulerian-Lagrangian (CELC) mechanistic model of seed dispersal (Nathan et al 2002), reducing CELC into an inverse-Gaussian (Wald) function with two parameters representing simple combinations of key physical and biological features of seed dispersal by wind. In this simplified form, WALD has a moment-generating function (Thompson and Katul 2008), allowing us to use Neubert and Caswell's (2000) analytical approach, whereas previous studies incorporating WALD into a spread model have analyzed the relative effects of dispersal parameters only through simulations (Jongejans et al 2008, Nathan et al 2011. While simulations enable a large area of parameter space to be explored, the analytical approach has the following advantages: (1) it is computationally efficient, (2) it provides tractable results, based on direct links between parameters and outcomes, (3) unlike simulation approaches it does not require statistical (e.g., regression) analysis of the model outputs (Wisdom et al 2000), and (4) it allows for a high level of standardization (Caswell 2001) enabling multispecies comparisons.…”

“…The recent explosion of interest in LDD has led to new methods for quantifying and understanding dispersal (Nathan et al 2003, Bullock et al 2006). New models of spread have incorporated LDD with demography (Jongejans et al 2008, Soons and Bullock 2008, Thompson and Katul 2008, Nathan et al 2011. However, the importance of individual mechanistic dispersal parameters on population spread has been mostly assessed by simulation approaches (Jongejans et al 2008, Thompson and Katul 2008, Coutts et al 2011, Nathan et al 2011.…”

Cumulative herbivory outpaces compensation for early floral damage on a monocarpic perennial thistle

“…Such herbivory can dramatically and quantitatively reduce plant-reproductive success (Louda and Potvin 1995;McCall and Irwin 2006;LucasBarbosa 2016) and directly affect plant population growth rate (Rose et al 2005;Tenhumberg et al 2008;von Euler et al 2014) and population density (Louda 1983;Jongejans et al 2008;Lehndal et al 2016). Floral herbivore impacts should, therefore, favor plant growth and allocation strategies that can reduce losses, or even improve fitness, under herbivory pressure (Fornoni 2011;Agrawal et al 2012;Carmona and Fornoni 2013).…”