A population genetic evaluation of ecological restoration with the case study on <Emphasis Type="Italic">Cyclobalanopsis myrsinaefolia</Emphasis> (Fagaceae)

The ultimate goal of ecological restoration is to create a self-sustaining ecosystem that is resilient to perturbation without further assistance. Genetic variation is a prerequisite for evolutionary response to environmental changes. However, few studies have evaluated the genetic structure of restored populations of dominant plants. In this study, we compared genetic variation of the restored populations with the natural ones in Cyclobalanopsis myrsinaefolia, a dominant species of evergreen broadleaved forest. Using eight polymorphic microsatellite loci, we analyzed samples collected from restored populations and the donor population as well as two other natural populations. We compared the genetic diversity of restored and natural populations. Differences in genetic composition were evaluated using measurements of genetic differentiation and assignment tests. The mean number of alleles per locus was 4.65. Three parameters (A, A _R, and expected heterozygosity) of genetic variation were found to be lower, but not significantly, in the restored populations than they were in the natural populations, indicating a founder effect during the restoration. Significant but low F _ST (0.061) was observed over all loci, indicating high gene flow among populations, as expected from its wind-pollination. Differentiation between the two restored populations was smallest. However, differences between the donor population and the restored populations were higher than those between other natural populations and the restored populations. Only 13.5% and 25.7% individuals in the two restored populations were assigned to the donor population, but 54.1 and 40% were assigned to another natural population. The genetic variation of the donor population was lowest, and geographic distances from the restoration sites to the donor site were much higher than the other natural populations, indicating that the present donor likely was not the best donor for these ecological restoration efforts. However, no deleterious consequences might be observed in restored populations due to high observed heterozygosity and high gene flow. This study demonstrates that during the restoration process, genetic structures of the restored populations may be biased from the donor population. The results also highlight population genetic knowledge, especially of gene flow-limited species, in ecological restoration.     

The influence of water content and leaf anatomy on carbon isotope discrimination and photosynthesis in Sphagnum

The relative effect of diffusional resistance due to water films (r_wf) and leaf anatomy (r_p) on rates of net photosynthesis and on-line measures of carbon isotope discrimination (Δ=Δδ¹³C) was investigated in Sphagnum. Sphagnum species differ in the exposure of photosynthetic cells at the leaf surface. In S. affine, photosynthetic cells are widely exposed at the surface, whereas in S. magellanicum, photo-synthetic cells are enclosed within water-filled hyaline cells. This difference is expected to lead to variation in diffusive resistance within leaves (r_p). Net photosynthesis and on-line Δ were measured at two water contents: greenhouse water content (wet) and blotted dry (dry). Without correcting for respiration, on-line Δ values differed significantly between wet (23.7%_o) and dry (30.9%_o) plants. However, there was no significant difference between species means and no species × water content interaction. Corrections for respiration lowered Δ values by approximately 8.1%_o and reduced the mean difference to 3.1%_o, but did not alter the rank order of treatments. Net photosynthesis also decreased by 16% in wet plants, but there was no significant difference between the two species. In addition, five populations of S. affine and S. magellanicum grown in a common garden were analysed for their organic matter carbon isotope composition (δ¹³C). These values varied more within each species (0.9–1.2%_o) than between the two species (0.6%_o). Therefore, we conclude that variation in surface water films leads to a greater difference in resistance to CO₂ uptake and carbon isotope discrimination than that due to variation in leaf anatomical properties in Sphagnum.     

Genetic variation in basic density and modulus of elasticity of coastal Douglas-fir

Douglas-fir trees from 39 open-pollinated families at four test locations were assessed to estimate heritability of modulus of elasticity (MOE) and basic density. After trees were felled, sound velocity was measured on 4-m logs with the Director HM200. Disks were taken to estimate dry and green wood density; dynamic MOE was estimated as green density × (sound velocity)². Heritability estimates of MOE (across-site h ²=0.55) were larger than those for total height (0.15) and diameter at breast height (DBH; 0.29), and similar to those for density (0.59). Negative genetic correlations were found for MOE with height (r _A=−0.30) and DBH (r _A=−0.51), and were similar to those found for density with height (r _A=−0.52) and DBH (r _A=−0.57). The partial correlations of height with MOE and density, while holding DBH constant, were positive, implying that the observed negative correlations between height and the wood properties were a function of the high positive correlation between height and DBH and the strong negative correlations between DBH and the wood properties. Taper [DBH/(height−1.4)] was found to be negatively associated with MOE. Selection for MOE may produce greater gains than selection for density because MOE had a larger coefficient of additive variation (9.6%) than density (5.1%). Conversely, selection for growth may have a more negative impact on MOE than density because of the greater genetic variation associated with MOE. Family mean correlations of the wood quality traits with stem form and crown health were mostly nonsignificant.     

INFERENCES ABOUT QUANTITATIVE INHERITANCE BASED ON NATURAL POPULATION STRUCTURE IN THE YELLOW MONKEYFLOWER,MIMULUS GUTTATUS

We used a nonmanipulative, marker-based method to study quantitative genetic inheritance in two habitats of a common monkeyflower population. The method involved regressing quantitative trait similarity on marker-estimated relatedness between individuals sampled in the field. We sampled 300 adult plants from each of two transects, one along a stream habitat and another through a meadow habitat. For each plant we measured 10 quantitative characters and assayed 10 polymorphic isozyme loci. In the meadow habitat, relatedness of plants within 1 m was moderate (r = 0.125, corresponding to half-sibs) as was actual variance of relatedness (V_r = 0.044). Significant heritabilities of 50–70% were found for corolla width and the fitness characters of flower number and plant weight. Genetic correlations were strongly positive, but sharing of environmental effects within 1 m was weak. In the stream habitat, levels of relatedness were lower and similar heritabilities were indicated. To detect dominance variance and the correlation of phenotypes due to shared inbreeding, we also estimated higher-order coefficients of relationship and inbreeding, but these did not significantly differ from zero. Laboratory-based estimates of heritability in the field were lower than the marker-based estimates, indicating that natural heritabilities and genetic correlations may be stronger than indicated by controlled studies.     

Selfing rates of pearl millet (Pennisetum typhoides Stapf and Hubb.) under natural conditions

The selfing rate of pearl millet (Pennisetum typhoides Stapf and Hubb.) has been determined under natural conditions. This species is said to be allogamous. Nine test plants homozygous for a particular allele on the alcohol dehydrogenase: ADH A locus (A₁A₁) were sown 2.5 m one from each other interspersed among 300 plants homozygous for the same locus (A₂A₂); these nine plants served as indicators of selfing. In the 20 spikes produced by these a test plants, the selfing rates varied between 2.2% and 21.7%. Selfmg rates were not significantly different within spikes of the same plant, except for one individual. There was no significant correlation between the rate of selfing and the density of the pollen shadow (estimated from the number of spikes producing pollen during the female phase of test plants) or variation in protogyny.     

Natural selection and neutral evolutionary processes contribute to genetic divergence in leaf traits across a precipitation gradient in the tropical oak Quercus oleoides

The impacts of drought are expanding worldwide as a consequence of climate change. However, there is still little knowledge of how species respond to long‐term selection in seasonally dry ecosystems. In this study, we used Q_ST‐F_ST comparisons to investigate (i) the role of natural selection on population genetic differentiation for a set of functional traits related to drought resistance in the seasonally dry tropical oak Quercus oleoides and (ii) the influence of water availability at the site of population origin and in experimental treatments on patterns of trait divergence. We conducted a thorough phenotypic characterization of 1912 seedlings from ten populations growing in field and greenhouse common gardens under replicated watering treatments. We also genotyped 218 individuals from the same set of populations using eleven nuclear microsatellites. Q_ST distributions for leaf lamina area, specific leaf area, leaf thickness and stomatal pore index were higher than F_ST distribution. Results were consistent across growth environments. Genetic differentiation among populations for these functional traits was associated with the index of moisture at the origin of the populations. Together, our results suggest that drought is an important selective agent for Q. oleoides and that differences in length and severity of the dry season have driven the evolution of genetic differences in functional traits.     

Demography, and genetic and morphological variability of the endangered Sophronitis sincorana (Orchidaceae) in the Chapada Diamantina, Brazil

We carried out a demographic study and evaluated the genetic and morphological variability in five populations of the endangered Sophronitis sincorana (Orchidaceae) endemic to Northeastern Brazil, based on allozyme and morphometric analyses. Plant density was approximately 0.5 plants/m², and the projected total number of plants was approximately 50,000 individuals. However, fruit set and recruitment of individuals are rare. The genetic variability was very high in all populations (P = 100, A = 3.0−3.5, H _e = 0.33−0.48), and all populations presented similar values of morphological variability. Low genetic and morphological structuring were found in the species (F _ST = 0.053, A_MRPP = 0.018). The elevated coefficient of endogamy encountered in populations of S. sincorana indicates the occurrence of structuring within the populations. The lack of correlation between morphological and genetic variation in this species indicates that none of the markers examined should be used separately for either conservation purposes.     

Demographic factors and genetic variation influence population persistence under environmental change

Population persistence has been studied in a conservation context to predict the fate of small or declining populations. Persistence models have explored effects on extinction of random demographic and environmental fluctuations, but in the face of directional environmental change they should also integrate factors affecting whether a population can adapt. Here, we examine the population‐size dependence of demographic and genetic factors and their likely contributions to extinction time under scenarios of environmental change. Parameter estimates were derived from experimental populations of the rainforest species, Drosophila birchii, held in the lab for 10 generations at census sizes of 20, 100 and 1000, and later exposed to five generations of heat‐knockdown selection. Under a model of directional change in the thermal environment, rapid extinction of populations of size 20 was caused by a combination of low growth rate (r) and high stochasticity in r. Populations of 100 had significantly higher reproductive output, lower stochasticity in r and more additive genetic variance (V_A) than populations of 20, but they were predicted to persist less well than the largest size class. Even populations of 1000 persisted only a few hundred generations under realistic estimates of environmental change because of low V_A for heat‐knockdown resistance. The experimental results document population‐size dependence of demographic and adaptability factors. The simulations illustrate a threshold influence of demographic factors on population persistence, while genetic variance has a more elastic impact on persistence under environmental change.     

A Study of Conservation Genetics in Cupressus chengiana,an Endangered Endemic of China,Using ISSR Markers

ISSR markers were used to analyze the genetic diversity and genetic structure of eight natural populations of Cupressus chengiana in China. ISSR analysis using 10 primers was carried out on 92 different samples. At the species level, 136 polymorphic loci were detected. The percentage of polymorphic bands (PPB) was 99%. Genetic diversity (H _e) was 0.3120, effective number of alleles (A _e) was 1.5236, and Shannon’s information index (I) was 0.4740. At the population level, PPB = 48%, A _e=1.2774, H _e=0.1631, and I=0.2452. Genetic differentiation (G _st) detected by Nei’s genetic diversity analysis suggested 48% occurred among populations. The partitioning of molecular variance by AMOVA analysis indicated significant genetic differentiation within populations (54%) and among populations (46%; P < 0.0003). The average number of individuals exchanged between populations per generation (N _m ) was 0.5436. Samples from the same population clustered in the same population-specific cluster, and two groups of Sichuan and Gansu populations were distinguishable. A significantly positive correlation between genetic and geographic distance was detected (r=0.6701). Human impacts were considered one of the main factors to cause the rarity of C. chengiana, and conservation strategies are suggested based on the genetic characters and field investigation, e.g., protection of wild populations, reestablishment of germplasm bank, and reintroduction of more genetic diversity.     

Analysis of Genetic Diversity and Population Structure in Sophora japonica Linn. in China With Newly Developed SSR Markers

Sophora japonica is a medium-sized deciduous native tree to China. Its flower buds and fruits have special medicinal value. By using 26 highly variable nuclear microsatellites, newly reported here, we assessed the genetic diversity and population structure of 10 representative populations (180 individuals in total) within the species. The results revealed a relatively high genetic diversity in S. japonica (N_a?=?8.00, H_e?=?0.74, PIC?=?0.80, I?=?1.67), and reduced genetic variation and heterozygote excess were detected in landrace populations (N_a?=?5.59, H_e?=?0.71, A_r?=?4.11, F_IS?=???0.043) when compared with those semi-wild population (N_a?=?9.7, H_e?=?0.74, A_r?=?8.80, F_IS?=?0.082). A significant bottleneck was detected in two Landraces populations. Moderate differentiation and frequent gene flow were detected among all populations (F_ST?=?0.079, P?<?0.05, N_m?=?2.893). Mantel test detected a marginal significant pattern of isolation by distance (r?=?0.009, P?=?0.50), and strong differentiation was observed between most southern and northern populations both by the STRUCTURE clustering and principal coordinate analysis (PCoA), indicating that geographic isolation played a key role in the genetic differentiation of the species. The results from this study will benefit the breeding and conservation of S. japonica, other congener species, and tree species with similar life history traits.

     

Spatiotemporal mating pattern variation in a wind‐pollinated Mediterranean shrub

Spatiotemporal variation in mating patterns is poorly known in wind‐pollinated plant species. Here, we analysed mating patterns of the wind‐pollinated dioecious shrub Pistacia lentiscus by genotyping 904 seeds from 30 mother plants with eight microsatellite markers in a high‐density population in two consecutive flowering seasons. We found significant differences in some mating system estimates between years, particularly in the levels of correlated paternity. Overall, within‐mothers correlated paternity was higher in 2007 than in 2006 (r_pWM = 0.085 and 0.030), which translated into an effective number of fathers (N_ep) of 11.8 and 33.6 respectively. Using a smoothing interpolation technique, we show that the effective pollen cloud was spatially structured in patches of high‐ and low‐genetic diversity, which do not remain constant from year to year. In 2006, the among‐mothers correlated paternity (r_pAM) showed no trend with distance, suggesting no restriction of pollen dispersal. However, in 2007, r_pAM was greater than zero at short distances, revealing the existence of small‐scale patterns of pollen dispersal. The fact that the studied seasons were climatically homogeneous during the flowering time suggested that the observed differences might be ascribed to between‐year phenological variation of individuals in the studied population or other (unknown) factors. Numerical simulations, based on the real data set, indicated that the clumping of males and decreasing plant density, which is related to different types of pollen limitation, greatly increase correlated mating in this wind‐pollinated species, which is of relevance under the frame of the continuous anthropogenic habitat disturbance suffered by Mediterranean ecosystems.     

Sexual reproduction, clonal diversity and genetic differentiation in patchily distributed populations of the temperate forest herb Paris quadrifolia (Trilliaceae)

Clonal plant species have been shown to adopt different strategies to persist in heterogeneous environments by changing relative investments in sexual reproduction and clonal propagation. As a result, clonal diversity and genetic variation may be different along environmental gradients. We examined the regional and local population structure of the clonal rhizomatous forest herb Paris quadrifolia in a complex of forest fragments in Voeren (Belgium). Relationships between population size (the number of shoots), shoot density (the number of shoots per m²) and local growth conditions were investigated for 47 populations. Clonal diversity and genetic variation within and among 19 populations were investigated using amplified fragment length polymorphism markers. To assess the importance of sexual reproduction, seed set, seed weight and germination success were determined in 18 populations. As predicted, local growth conditions largely affected population distribution, size and density of P. quadrifolia. Populations occurring in moist and relatively productive sites contained significantly more shoots. Here, shoots were also much more sparsely distributed compared to populations occurring in dry and relatively unproductive sites, where shoots showed a strongly aggregated distribution pattern. Clonal diversity was relatively high, compared with other clonal species (G/N ratio = 0.43 and Simpson’s D=0.81). Clonal diversity significantly (P<0.01) decreased with increasing shoot density while molecular genetic variation was significantly (P<0.01) affected by population size and local environmental conditions. Lack of recruitment and out-competition of less-adapted genotypes may explain the decreased genetic variation in dry sites. Analysis of molecular variance revealed significant genetic variation among populations (Φ _ST=0.42, P<0.001), whereas pairwise genetic distances were not correlated to geographic distances, suggesting that gene flow among populations is limited. Finally, the number of generative shoots, the number of seeds per fruit and seed weight were significantly and positively related to population size and local growth conditions. We conclude that under stressful conditions populations of clonal forest plant species can slowly evolve into remnant populations characterized by low levels of genetic variation and limited sexual reproduction. Conservation of suitable habitat conditions is therefore a prerequisite for effective long-term conservation of clonal forest plant species.     

A new method to estimate individual dry weights of rotifers

Body and egg volumes of 12 rotifer species of Lake Constance were calculated from more than 18 000 individually measured animals using geometric approximations. Body (V _A) and egg (V _E) volumes of various rotifer species have an allometric relationship described by: V _E = 1272 · V _A ^0.3379, while the relation V _E/V _A for each species was constant ranging from 0.016 to 0.87. Dry weight of adult rotifers was assumed to be the sum of the egg dry weight plus a corrected weight increment from egg to adult. It was estimated with the formula W _A = W _E · (1 + a · F _A/F _E) where (a) was varied between 0 and 0.1. Egg dry weight content was assumed to be 35 % of fresh weight. The estimates of dry weight to wet weight ratios ranged from 0.57 % (Asplanchna priodonta) to 29.4 % (Kellicottia longispina). Dry weight estimates obtained with this method are comparable to those obtained with direct measurements of dry weight or carbon content.This investigation was supported by the Deutsche Forschungsgemeinschaft within the Special Collaboration Program (SFB) Cycling of Matter in Lake Constance.     

Wild genetic diversity preservation in a small-sized first generation breeding population of <Emphasis Type="Italic">Allanblackia floribunda</Emphasis> (Clusiaceae)

Founder group size is of prime importance in tree breeding programs. We determined whether sampling 20-plus trees for breeding in Allanblackia floribunda, a tropical forest tree species that has been recently enrolled in tree improvement program for fruit and seed production, would affect neutral genetic diversity and inbreeding level in both breeding and production populations. Using eight informative microsatellite loci, we: (a) assessed the nuclear genetic diversity of ten natural populations, and of the breeding population in the humid forest zone of Cameroon; (b) investigated temporal effective-size fluctuations in A. floribunda natural populations, with a view to identifying the role of past demographic events in the genetic structure of the studied species; and (c) tested the hypothesis that genetic diversity in a founder group of 20 individuals is not different from that existing in the wild. The eight loci were variable. High levels of genetic diversity (A = 4.96; H _E = 0.59) and moderate differentiation (R _ST = 0.061) were found within and among populations in wild stands. High genetic distances existed between populations ( \textaverage chord distance = 0.\text2769 ±0.00\text554 ) \left( {{\text{average chord distance}} = 0.{\text{2769}} \pm 0.00{\text{554}}} \right) . Eight of the ten surveyed populations showed signs of deviation from mutation-drift equilibrium, suggesting Pleistocene population bottlenecks and fluctuations in effective population size. Mantel tests did not reveal any relationships between genetic and geographic distances. A neighbor-joining dendrogram showed a population structure that could be explained by historical factors. The hypothesis tested has been accepted. However, a slight increase in inbreeding was observed in the breeding population.     

Landscape features impact connectivity between soil populations: a comparative study of gene flow in earthworms

Landscape features are known to alter the spatial genetic variation of aboveground organisms. Here, we tested the hypothesis that the genetic structure of belowground organisms also responds to landscape structure. Microsatellite markers were used to carry out a landscape genetic study of two endogeic earthworm species, Allolobophora chlorotica (N = 440, eight microsatellites) and Aporrectodea icterica (N = 519, seven microsatellites), in an agricultural landscape in the North of France, where landscape features were characterized with high accuracy. We found that habitat fragmentation impacted genetic variation of earthworm populations at the local scale. A significant relationship was observed between genetic diversity (H_e, A_r) and several landscape features in A. icterica populations and A. chlorotica. Moreover, a strong genetic differentiation between sites was observed in both species, with a low degree of genetic admixture and high F_st values. The landscape connectivity analysis at the regional scale, including isolation by distance, least‐cost path and cost‐weighted distance approaches, showed that genetic distances were linked to landscape connectivity in A. chlorotica. This indicates that the fragmentation of natural habitats has shaped their dispersal patterns and local effective population sizes. Landscape connectivity analysis confirmed that a priori favourable habitats such as grasslands may constitute dispersal corridors for these species.     

Estimating the capacity of Chamaecrista fasciculata for adaptation to change in precipitation

Adaptation through natural selection may be the only means by which small and fragmented plant populations will persist through present day environmental change. A population's additive genetic variance for fitness (V_A(W)) represents its immediate capacity to adapt to the environment in which it exists. We evaluated this property for a population of the annual legume Chamaecrista fasciculata through a quantitative genetic experiment in the tallgrass prairie region of the Midwestern United States, where changing climate is predicted to include more variability in rainfall. To reduce incident rainfall, relative to controls receiving ambient rain, we deployed rain exclusion shelters. We found significant V_A(W) in both treatments. We also detected a significant genotype‐by‐treatment interaction for fitness, which suggests that the genetic basis of the response to natural selection will differ depending on precipitation. For the trait‐specific leaf area, we detected maladaptive phenotypic plasticity and an interaction between genotype and environment. Selection for thicker leaves was detected with increased precipitation. These results indicate capacity of this population of C. fasciculata to adapt in situ to environmental change.     

Genetic diversity of fragmented populations of<Emphasis Type="Italic"> Polygala reinii</Emphasis> (Polygalaceae), a perennial herb endemic to Japan

Genetic variation at 10 allozyme loci was analyzed in 14 populations of Polygala reinii (Polygalaceae), a perennial herb endemic to central Honshu, Japan, with a fragmented geographical distribution. The levels of genetic variation within species (P=80.0, A=3.10, H_E=0.303) and within populations (P=42.1, A=1.61, H_E=0.163) were considerably higher than the mean for other endemic plants or short-lived perennial herbs. Genetic differentiation among populations was also high (G_ST=0.404). The genetic distance phenogram tended to show a clustering of the populations reflecting the fragmentation of the species range. A principal component analysis revealed the same tendency, as well as three groupings of populations in the Tokai district, on the Kii Peninsula and in the northern Kinki district. A negative correlation was obtained between the levels of gene flow and geographical distance among the populations (r=–0.745, P<0.0001). These results indicated limited gene flow among populations in P. reinii, presumably due to the geographical isolation accompanying the fragmented distribution. On the other hand, the geographical differentiation between the Japan Sea and Pacific Ocean sides was found in P. reinii, suggesting the influence of postglacial migration on the establishment of the genetic structure of this species.     

Design and use of a simulation model to evaluate germplasm for antibiotic resistance to the greenhouse whitefly (Trialeurodes vaporariorum) and the sweetpotato whitefly (Bemisia tabaci)

SARAH (Software for theAssessment of antibioticResistance toAleyrodidae inHost plants) is a deterministic simulation model of whitefly population growth based on whitefly life-history components determined on individual plants. The life-history components recorded were oviposition rate, adult survival, pre-adult survival, developmental period, and sex ratio. The simulation model serves as a tool to combine these components and to obtain a single criterion for (antibiotic) resistance. The criterion used was the decrease in simulated intrinsic population growth rate, r _s , relative the r _s value determined on a susceptible control genotype. This model-based evaluation method was tested using the greenhouse whitefly,Trialeurodes vaporariorum Westwood, on tomato and the sweetpotato whitefly,Bemisia tabaci Gennadius, on tomato, eggplant, collard, and pepper. To study its consistency over time, the evaluation method was repeated six times forT. vaporariorum on a susceptible and a resistant tomato cultivar. Simulated intrinsic population growth rate was more consistent in indicating resistance than any of the individual life-history components. Of tenL. hirsutum accessions tested for resistance toT. vaporariorum, three exhibited r _s values that were significantly lower than those for the susceptible control. In addition, on these tenL. hirsutum accessions, a significant positive correlation was observed between r _s and sex ratio (# females/# males). Four host plant species (tomato, collard, eggplant, and pepper) were evaluated for resistance toB. tabaci. All life-history components and r _s values varied among host species, while a negative r _s value was observed forB. tabaci on pepper. A high correlation was found between results from a sensitivity analysis of SARAH and results from a sensitivity analysis of a validated whitefly population simulation model by Yanoet al. (1989a). Significant correlations were found for the relationships between oviposition rate, adult survival, or pre-adult survival and r _s , indicating that none of these life-history components can be omitted from the test procedure. This model-based evaluation method offers a standardized way to quantify levels of antibiotic resistance to whiteflies and will enhance efficiency in breeding programs.     

Photosynthesis, Chlorophyll Fluorescence and Within-Canopy Distribution of Epiphytic Ferns in a Mexican Cloud Forest

Abstract: Parameters associated with the photosynthetic performance of eight common epiphytic ferns in a Mexican cloud forest were investigated in relation to the distribution of these species within the canopy. If the substantial microclimatic gradients within tropical forest canopies provide microhabitats exploited by different epiphytic species, we would expect to find correlations between distribution and physiological traits. Maximum rates of CO₂ uptake (A_max) and photon flux densities at light compensation points (LCP) were in the range of shade plants (A_max = 0.6 ‐ 5.2 μmol m^‐2 s^‐1; LCP = 4 ‐ 6.5 μmol m^‐2 s^‐1), but saturation light intensities were more typical for sun plants (270 ‐ 550 μmol m^‐2 s^‐1). A_max and nitrogen content per unit dry weight were correlated with the distribution of the species within the canopy, but LCP, apparent quantum yield and dark respiration were not. When leaves were left to desiccate, the fluorescence yield of dark‐adapted leaves (Y₀) remained high until the relative water content (RWC) had dropped below 30 to 20 %. Fluorescence after short illumination with 200 μmol m^‐2 s^‐1 declined when RWC dropped below 70 to 40 %. After exposure to full sunlight for 1 h, Y₀ of species growing in the outer canopy (Pleopeltis mexicana and Polypodium plebeium) and a plant characteristic of the mid‐canopy (Elaphoglossum petiolatum) recovered better than in species from shadier locations (Trichomanes bucinatum, Asplenium cuspidatum, Phlebodium areolatum). With the exception of Ph. areolatum and a species growing at both exposed and shaded sites (Polypodium puberulum), Y₀ recovered at least partially after a loss of 80 ‐ 96 % of saturation water, with the humidity‐loving filmy fern (T. bucinatum) showing no signs of permanent damage at all. The results suggest that tolerance or avoidance of desiccation and high light may be at least as important in controlling the distribution of the species studied as photosynthetic performance without stress.