Modeling body size evolution in Felidae under alternative phylogenetic hypotheses

The use of phylogenetic comparative methods in ecological research has advanced during the last twenty years, mainly due to accurate phylogenetic reconstructions based on molecular data and computational and statistical advances. We used phylogenetic correlograms and phylogenetic eigenvector regression (PVR) to model body size evolution in 35 worldwide Felidae (Mammalia, Carnivora) species using two alternative phylogenies and published body size data. The purpose was not to contrast the phylogenetic hypotheses but to evaluate how analyses of body size evolution patterns can be affected by the phylogeny used for comparative analyses (CA). Both phylogenies produced a strong phylogenetic pattern, with closely related species having similar body sizes and the similarity decreasing with increasing distances in time. The PVR explained 65% to 67% of body size variation and all Moran's I values for the PVR residuals were non-significant, indicating that both these models explained phylogenetic structures in trait variation. Even though our results did not suggest that any phylogeny can be used for CA with the same power, or that “good” phylogenies are unnecessary for the correct interpretation of the evolutionary dynamics of ecological, biogeographical, physiological or behavioral patterns, it does suggest that developments in CA can, and indeed should, proceed without waiting for perfect and fully resolved phylogenies

A new method of growth analysis for plants that experience periodic losses of leaf mass

1. A new method (the iterative approach) is presented by which growth analyses can be conducted on plants that have been subjected to significant losses in biomass and leaf area between harvests. The method is particularly useful to analyse the effects of defoliation on growth and biomass allocation. 2. Values for the following parameters can be estimated: absolute growth rate (g day-1), relative growth rate (RGR, g g-1 day-1), net assimilation rate (NAR, g m-2 day-1), leaf area ratio (LAR, m2 g-1), fraction of newly assimilated mass that is allocated to leaf lamina production (flam, g g-1), and daily fractional change in the average specific leaf area of plants (ρ, day-1). These parameters are determined by means of iterations. We defined a number of growth functions, and the values of NAR, flam and the SLA of newly produced leaves were changed until these functions correctly predicted the measured total plant mass, leaf lamina mass and leaf area at the end of the growth period. This avoids having to assume a constant relationship between leaf area and biomass (as in the 'classical' approach), and it avoids the use of polynomial functions to fit growth data (as in the 'functional' approach) that are unsuitable for fitting data sets exhibiting discontinuities such as abrupt changes in biomass. 3. The method was applied to a greenhouse experiment in which we analysed the effects of sustained defoliation on growth and biomass allocation in a tropical understorey palm, Chamaedorea elegans Mart. 4. We showed that C. elegans plants respond to defoliation with a considerable increase in the allocation of new assimilates to lamina growth (flam) and that, despite the repeated loss of leaf area and associated reductions in LAR, they had RGR values that were similar to those of undamaged plants.</p

Canopy-level photosynthetic compensation after defoliation in a tropical understorey palm

1. Increases in photosynthesis of leaves remaining after defoliation may result from shifts in leaf photosynthetic characteristics or from an improved light penetration in the canopy. However, few studies have tried to estimate the relative contribution of these factors to mitigating the negative effects of defoliation. We present a quantitative framework for such an analysis. 2. In a field and greenhouse experiment, plants of the rain forest understorey palm Chamaedorea elegans were subjected to three levels of defoliation (0, 50 or 66% of leaves removed) and, in the greenhouse, grown at two irradiances (5 or 16% of daylight, 'low light' and 'high light' hereafter). For each plant, leaf photosynthesis and light penetration in the canopy were measured and these data were used to calculate whole-canopy carbon gain. 3. Defoliation significantly increased the light available to the remaining leaves. In the field and in the 'high-light' greenhouse plants, defoliation also resulted in an increase in the light-saturated photosynthesis per unit leaf area (Pmax), although in the 'low-light' plants this was not the case. 4. A sensitivity analysis revealed that in the 'low-light' plants, a proportional increase in leaf Pmax did not result in increased canopy-level carbon gain, while in the 'high-light' and field plants, it did. This suggests that the lack of plasticity in Pmax in response to defoliation, at low light, may be the appropriate pattern to maximize carbon gain. 5. Defoliated plants had 10-18% more average photosynthesis per unit leaf area (Parea) than the control plants, and this increase was mostly the result of an improved light penetration in the canopy. 6. A relatively small fraction (5-30%) of the total estimated loss in canopy carbon gain caused by the removal of leaves was compensated for by an increase in Parea. This suggests that in rain forest understorey plants, an increase in diurnal photosynthesis of remaining leaves has limited potential for mitigating the negative effects of defoliation.</p

Defoliation and gender effects on fitness components in three congeneric and sympatric understorey palms

1.Rain forest understorey perennial plants can be frequently exposed to leaf area losses induced by herbivory or physical damage from falling canopy debris. In dioecious species, tolerance to defoliation may differ between genders (e.g. females may suffer more than males), but this topic has so far received little attention. 2.Here, we quantified gender-dependent effects of increased levels (0–100%) of sustained defoliation (applied bi-annually for 2 years) on vital rates in three economically important dioecious understorey palm species in the genus Chamaedorea (C. elegans, C. ernesti-augustii and C. oblongata). We also quantified gender differences in functional and life-history traits and assessed the direct reproductive costs in terms of biomass allocation to reproduction. 3.In the three species, non-defoliated (control) females were smaller and had three to seven times higher reproductive allocation than males. 4.Defoliation did not affect survivorship in any of the three species, except in the 100% defoliation treatment. Stem growth (RGR) and especially reproduction (probability of reproduction and reproductive output) were negatively affected by defoliation. Females of C. ernesti-augustii suffered higher mortality than males at 100% defoliation, but this was not the case for the other two species. Also, only in C. ernesti-augustii females exhibited lower RGR than males. In all species, the probability of reproduction did not differ between genders. The reproductive output (production rate of inflorescences) differed among genders only in C. ernesti-augustii, where males were more productive than females. 5.Interestingly, in most cases, defoliation effects on vital rates did not differ significantly between males and females, indicating that tolerance to defoliation was similar between genders. Such results were independent of plant size (stem length). 6.Synthesis. Our results do not support the prevailing theory that the greater reproductive costs of females will lead to reduced tolerance to stresses such as defoliation. The implications of these results and their importance for designing sustainable leaf harvesting regimes are discussed