The effect of soil on the growth performance of tropical species with contrasting distributions

Within the tropics, a marked gradient in rainfall between dry and wet forests correlates with a well documented turnover of plant species. While water availability along these gradients is an important determinant of species distributions, other abiotic and biotic factors correlate with rainfall and may also contribute to limit species distribution. One of these is soil fertility, which is often lower in the wetter forests. To test its possible role in species distribution along a rainfall gradient, we performed a screen‐house experiment where we measured the growth performance of seedlings of 23 species with contrasting distributions across the Isthmus of Panama. We grew seedlings in soils collected from the drier Pacific side and the wetter Atlantic side. Differences in soil fertility across the Isthmus were large enough to significantly influence the growth performance of the seedlings. However, we found no evidence of home‐soil advantage among species with contrasting distributions. Dry‐distribution species grew on average slower than wet‐distribution species suggesting a cost to drought adaptations. The response to soil differences correlated with the growth rate of the species, such that fast‐growing species responded more to changes in soil quality. We hypothesize that inherently slow growth rates of some dry‐distribution tropical species may be a more important factor limiting their colonization of wetter sites along the rainfall gradient.     

Temperature effects on gametophyte life-history traits and geographic distribution of two cryptic kelp species

A major determinant of the geographic distribution of a species is expected to be its physiological response to changing abiotic variables over its range. The range of a species often corresponds to the geographic extent of temperature regimes the organism can physiologically tolerate. Many species have very distinct life history stages that may exhibit different responses to environmental factors. In this study we emphasized the critical role of the haploid microscopic stage (gametophyte) of the life cycle to explain the difference of edge distribution of two related kelp species. Lessonia nigrescens was recently identified as two cryptic species occurring in parapatry along the Chilean coast: one located north and the other south of a biogeographic boundary at latitude 29-30°S. Six life history traits from microscopic stages were identified and estimated under five treatments of temperature in eight locations distributed along the Chilean coast in order to (1) estimate the role of temperature in the present distribution of the two cryptic L. nigrescens species, (2) compare marginal populations to central populations of the two cryptic species. In addition, we created a periodic matrix model to estimate the population growth rate (λ) at the five temperature treatments. Differential tolerance to temperature was demonstrated between the two species, with the gametophytes of the Northern species being more tolerant to higher temperatures than gametophytes from the south. Second, the two species exhibited different life history strategies with a shorter haploid phase in the Northern species contrasted with considerable vegetative growth in the Southern species haploid stage. These results provide strong ecological evidence for the differentiation process of the two cryptic species and show local adaptation of the life cycle at the range limits of the distribution. Ecological and evolutionary implications of these findings are discussed.     

Difference in carbon weight of the immature stages of two co-existing species of blackflies (Diptera: Simuliidae) with contrasting reproductive strategies

Two species of blackflies (Diptera: Simuliidae) co-exist at a lake-outlet site in Finland. The adult females of one of them, Simulium noelleri Fried., are able to produce eggs without taking a blood meal; females of the other species, S. truncalum Ldstr., must suck blood before they can mature eggs. Female pupae, pharate adults and adults of S. noelleri are markedly heavier in carbon weight than males of this species, and of males and females of S. truncatum. Females of the former species develop a fat body during the larval stadia.     

The effects of winter stress on Sphagnum species with contrasting macro- and microdistributions

Introduction. Sphagnum L. forms much of the ground cover in northern peatlands. Different species show affinities for bioclimatic regions in Europe (oceanic/continental; northern/southern) and species-specific tolerance of winter conditions can be a factor explaining their distribution.

Methods. We focussed on low temperature in a series of experiments and tested (1) the innate ability of a selection of Sphagnum species to tolerate low temperature in relation to their micro-topographic (wetness) and geographical (climate) distribution; (2) the rate of cold tolerance acquisition; and (3) the ability of species to survive a range of low temperature once cold hardened.

Key results. Our experiments showed that maximal PSII efficiency (F_v/F_m, chlorophyll fluorescence), growth rates and survival were all negatively affected by sub-zero temperatures. Environmental conditions associated with the onset of winter (colder nights and shorter days) triggered the acquisition of cold tolerance in Sphagnum.

Conclusions. The results were not unequivocal, but species associated with colder climates were generally more tolerant of sub-zero conditions. Species associated with the wettest and driest ends of the wetness gradient were more consistent in their responses than those in between, with wetter-dwelling species being less sensitive to sub-zero temperature than species found in drier microhabitats. Overall, our results suggest that adaptation to winter conditions contribute to the current distribution patterns of Sphagnum species.     

Interactions among species with contrasting dispersal modes explain distributions for epiphytic lichens

Understanding how the biodiversity response to climate change will be modified at ecological scales, e.g. by species interactions, is a major challenge. Lichen epiphytes – the close interdependent relationship between a heterotrophic fungus and photosynthetic partner (photobiont) – are used here to explore how interaction regimes (between lichen species, and between lichens and their photobionts) explain distribution patterns along spatial climatic gradients. To do this we tested field evidence for the ‘core‐fringe hypothesis’, which proposes a facilitative interaction; sexually‐reproducing and spore‐dispersed lichens with a requirement for resynthesis with a compatible photobiont (Nostoc) are facilitated by the prior establishment of asexual lichens which disperse both the fungus and photobiont together. We used two closely related Nephroma species which differ in their reproductive mode – N. laevigatum (sexual spore‐dispersed) and N. parile (asexual) – and compared their occurrence along a bioclimatic gradient to local habitat factors, including the co‐occurrence of asexual lichens which have shared specificity for compatible Nostoc genotypes. The results showed that: 1) N. laevigatum is significantly more likely to occur on trees that have already been colonised by asexual lichens with shared specificity for Nostoc, supporting the core‐fringe hypothesis, while 2) N. parile is independent of this association (strengthening the core‐fringe hypothesis), with its response to a precipitation gradient modified by microhabitat factors. This positive test for the core‐fringe hypothesis demonstrates how interaction regimes can fundamentally alter expectations under climate change. There is an assumption that spore‐dispersed lichen species could more easily track their suitable bioclimatic space through fragmented habitat, compared to asexual species with larger and heavier propagules. However, the establishment of spore‐dispersed lichen epiphytes into new habitat may be limited by the dispersal rates of asexual species, which act as key facilitators.     

Temperature effects on the reactive oxygen species formation and antioxidant defence in roots of two cucurbit species with contrasting root zone temperature optima

Suboptimal root zone temperature (14°C) was imposed on chilling-sensitive cucumber (Cucumis sativus L.) and chilling-tolerant figleaf gourd (Cucurbita ficifolia Bouché) plants. Exposure of roots to low temperature for up to 10 days caused a strong growth inhibition in cucumber compared with figleaf gourd. Physiological analysis showed that generation of reactive oxygen species (ROS) such as hydrogen peroxide and superoxide anion was significantly induced in cucumber plants as fast as 1 day after low root zone temperature treatment. In addition to the significant induction of antioxidant superoxide dismutase activity, low root zone temperature also increased the mitochondrial electron transport allocated to alternative pathway while decreased cytochrome pathway salicylhydroxamic acid-resistant respiration. However, these defense responses could not compensate for the ROS production, resulting in membrane lipid peroxidation and loss of root cell viability in the low root zone temperature treated cucumber roots. In contrast, 14°C root zone temperature had no significant effects on figleaf gourd plant growth, antioxidant enzymes, ROS levels and alternative respiratory pathway. Hence, difference in ROS metabolism would be associated with the remarkable difference in adaptability of cucumber and figleaf gourd plants in response to suboptimal root zone temperature condition.     

The effects of intraspecific density dependence on species richness and species abundance distributions

Species richness and patterns of abundance result from the interplay between niche differences, realized as intraspecific density dependence (IDD), and so-called neutral processes that arise when species fitnesses are similar. This paper presents an extension of neutral models that incorporates delays in IDD that could result from resource-mediated competition or through a pathogen pool. These delays reduce standing species richness and qualitatively change the shape of species abundance distributions and render them consistent with the hollow curve shape even in the presence of strong IDD.     

Comparative ecophysiology of two representativeQuercus species appearing in different stages of succession

Ecophysiological comparisons were made of the growth and photosynthetic characteristics between seedlings of deciduousQuercus serrata and evergreenQuercus myrsinaefolia. Q. myrsinaefolia seedlings naturally occurring in secondary coppice forests showed exponential-like growth in height with age, while sympatricQ. serrata seedlings were considerably smaller in height, their growth being limited by shortage of light. The photosynthetic characteristics measured under laboratory conditions showed no bases for the differences in growth between the two species on the forest floor: Light compensation points of the seedlings raised under 5% daylight were almost identical for the two species, being about 6.0 μE·m⁻²·s⁻¹. Growth analysis of seedlings planted in a coppice forest showed that bothQ. serrata andQ. myrsinaefolia could hardly grow during the summer under the shrub layer, when relative photon flux density (RPFD) was 0.9±0.5%. In the winter, when RPFD under the leafless canopy increased to 29.3±2.7%, the dry matter production of the evergreen seedlings ofQ. myrsinaefolia was much improved. Current-year seedlings of the species showed NAR of 0.102±0.021 g·dm⁻²·mo⁻¹ during the winter. Temperature dependency of photosynthesis and increment of leaf temperature by direct solar beam also indicated active photosynthesis ofQ. myrsinaefolia on the forest floor during the winter.     

The contrasting effects of short-term climate change on the early recruitment of tree species

While interspecific competition is prevalent in natural systems, we do not yet understand how it can influence an individual’s phenotype within its lifetime and how this might affect performance. Morphology and swimming performance are two important fitness-related traits in fishes. Both traits are essential in acquiring and defending resources as well as avoiding predation. Here, we examined if interspecific competition could induce changes in morphology and affect the swimming performance of two strains of juvenile Atlantic salmon (Salmo salar). We imposed competitive scenarios on the fish using artificial streams containing different combinations of four interspecific competitors. Exposure to interspecific competitors induced morphological changes over time, through the development of deeper bodies, whereas controls free of interspecific competitors developed more fusiform body shapes. Furthermore, swimming performance was correlated to fusiform morphologies and was weaker for Atlantic salmon in competitive scenarios vs. controls. This implies that interspecific competition has direct effects on these fitness-related traits in Atlantic salmon. To the best of our knowledge, this is the first time that morphology, an important fitness-related trait linked to swimming performance, has been shown to be negatively impacted through interactions with an interspecific competitor.     

Geographic distributions and physiological characteristics of co-existing Flaveria species in south-central Mexico

The genus Flaveria consists of 23 species with significant variation in photosynthetic physiologies. We tested whether photosynthetic pathway variation in seven co-existing Flaveria species corresponds to geographic distributions or physiological performance in C₃, C₄, and intermediate species growing under natural conditions in south-central Mexico. We found that Flaveria pringlei (C₃) was the most widely distributed species with multiple growth habits. Numerous populations of Flaveria kochiana (C₄), a recently described species with a previously unknown distribution, were located in the Mixtec region of Oaxaca. Flaveria cronquistii (C₃) and Flaveria ramosissima (C₃-C₄) were only located in the Tehuacán Valley region while Flaveria trinervia (C₄) was widely distributed. Only one population of Flaveria angustifolia (C₃-C₄) and Flaveria vaginata (C₄-like) were located near Izúcar de Matamoros. Midday leaf water potential differed significantly between Flaveria species, but did not vary according to growth habit or photosynthetic pathway. The quantum yield of photosystem II did not vary between species, despite large differences in leaf nitrogen content, leaf shape, plant size and life histories. We did not find a direct relationship between increasing C₄ cycle characteristics and physiological performance in the Flaveria populations examined. Furthermore, C₃ species were not found at higher elevation than C₄ species as expected. Our observations indicate that life history traits and disturbance regime may be the primary controllers of Flaveria distributions in south-central Mexico.     

Differential effects of past climate warming on mountain and flatland species distributions: a multispecies North American mammal assessment

Aim The magnitude of predicted range shifts during climate change is likely to be different for species living in mountainous environments compared with those living in flatland environments. The southern edges of ranges in mountain species may not shift northwards during warming as populations instead migrate up available elevational gradients; overall latitudinal range appears therefore to expand. In contrast, flatland species should shift range centroids northwards but not expand or contract their latitudinal range extent. These hypotheses were tested utilizing Late Pleistocene and modern occurrence data. Location North America. Methods The location and elevation of modern and Late Pleistocene species occurrences were collected from data bases for 26 species living in mountain or flatland environments. Regressions of elevation change over latitude, and southern and northern range edges were calculated for each species for modern and fossil data sets. A combination of regressions and anova s were used to test whether flatland species shift range edges and latitudinal extents more than mountain species do. Results Flatland species had significantly larger northward shifts at southern range edges than did mountain‐dwelling species from the Late Pleistocene to the present. There was also a significant negative correlation between the amount of change in the latitude of the southern edge of the range and the amount of elevational shifting from the Late Pleistocene to the present. Although significant, only c. 25% of the variance could be explained by this relationship. In addition, there was a weak indication that overall range expansion was less in flatland‐dwelling than in mountain‐dwelling species. Main conclusions The approach used here was to examine past species’ range responses to warming that occurred after the last ice ages as a means to better predict potential future responses to continued warming. The results confirm predictions of differential southern edge and overall range shifts for species occupying mountain and flatland regions in North America. The findings may be broadly applicable in other regions, thus allowing better modelling of future range and distribution related responses.     

Sexual interference in two Chamerion species with contrasting modes of movement herkogamy

Evolution of herkogamy has been ascribed to preventing autonomous selfing within flowers, but this argument has received challenges due to the negative effects of sexual interference on reproductive success of plant species. We examined the effects of the two contrasting modes of herkogamy, detailed by the different patterns of style movement, on the foraging time of pollinators on flowers, pollen removal, and deposition in two Chamerion species. Our results suggested that the duration of foraging time of bumblebees was generally higher in C. angustifolium (L.) Holub than in C. conspersum (Hausskn.) Holub during the male-phase of flowers, but the reverse during the female-phase of flowers. As a result, stigma interfered with pollen removal more in C. conspersum than in C. angustifolium, based on examinations of pollen removal after one visit by a pollinator. However, this negative effect on total pollen removal was covered by the high pollinator diversity and the possible high visitation rate in the study sites. In contrast, we found that almost no difference existed in pollen deposition rate after one visit of a pollinator between the two Chamerion species, and emasculation did not increase the total pollen deposition in either species, indicating that anthers did not interfere with pollen deposition in the two Chamerion species. Our results suggested that, compared with C. conspersum, the derived mode of herkogamy in C. angustifolium reduced interference of stigmas in pollen removal. This might contribute to the wide distribution of C. angustifolium, to some degree, in environments of pollinator scarcity and low activity in newly colonized habitats.     

Responses to natural climatic variation and experimental warming in two tundra plant species with contrasting life forms: Cassiope tetragona and Ranunculus nivalis

Two circumpolar tundra plant species, the evergreen dwarfshrub Cassiope tetragona and the perennial herb Ranunculus nivalis , were studied at Latnjajaure in northern Swedish Lapland during three consecutive growing seasons (1993–95) as a contribution to the ITEX programme. Open-top chambers (OTCs) were used in a passive heating experiment, and the performance of the plants in unmanipulated controls was correlated with climatic fluctuations among the years. Phenological, vegetative, and reproductive variables were measured. In both species phenological responses were controlled mainly by ambient air temperature. In the evergreen C. tetragona vegetative growth was controlled mainly by the influx of global solar radiation and was not temperature-dependent, whereas the opposite applied in the herbaceous R. nivalis . Vegetative growth in C. tetragona was rather stable among years as well as between treatments, whereas it was strongly influenced by annual climate in R. nivalis . Both species increased their reproductive success with increasing temperature, but R. nivalis was also radiation-dependent in this case, probably because of its green, photosynthetic nutlets. Ovule number in R. nivalis increased steadily in the experimentally heated plots during the study in response to the constant temperature amelioration above the ambient. At the community level, evergreen C. tetragona seems to have low competitive ability under warmer conditions. The situation for vernal low-growing herbs like R. nivalis is more complex; despite a strong positive response to increased temperature, they may exhibit decreased reproductive success if overgrown by a vigorous graminoid canopy.     

Host‐plant dissections reveal contrasting distributions of Crematogaster ants and their symbionts in two myrmecophytic Macaranga species

1. Ant–plant mutualisms are among the most widespread and ecologically important insect–plant interactions in the tropics. The multitrophic mutualism involving Macaranga plants (Euphorbiaceae) and Crematogaster ants (Formicidae) is the most diverse in Southeast Asia. This interaction also includes trophobiotic scale insects (Coccidae) and nematodes inhabiting ant refuse piles. 2. Here two myrmecophytic systems were compared, Macaranga trachyphylla with Crematogaster captiosa (Mt + Cc) and Macaranga beccariana with Crematogaster decamera (Mb + Cd), using a fine‐scale dissection of the stems. For the two plant species, for each internode, both contents (ants, coccids, refuse piles) and structure (internode height, numbers of open and occluded ant holes) were recorded. 3. There were significant patterns in the vertical distribution of ant colonies and their symbionts in the plant stems. Most coccids were kept in the highest sections of both systems, although Mb + Cd hosted a broader range of coccid species than Mt + Cc. Three nematode species were recorded, but with a rather low specificity to plant or ant species. Furthermore, the fine‐scale distribution showed aggregation of closed holes with ant brood and separation of nematode‐infested refuse piles from eggs. 4. The results of this study indicate that ants manipulate spatial colony structure via distribution of brood, holes and the symbionts. It is suggested that ants optimise the location of refuse piles and occluded holes via spatial heterogeneity in their distribution among internodes. This paper discusses the protective role of occluded holes and demonstrates some general interactions with other symbiotic fauna.     

Specialization pays off: contrasting effects of two types of tannins on oak specialist and generalist moth species

Phytochemical coevolution theory posits that specialist herbivores will be less sensitive than generalists to the defensive compounds of their host. On the other hand, both types of herbivores should allegedly be similarly sensitive to ‘quantitative’ defences, such as tannin compounds. In this paper, we critically examine the biological effects of two types of tannins: vescalagin (a quantitatively dominant hydrolysable tannin of Quercus robur), and a mix of condensed tannins. In a phylogenetically controlled design, we compare the response of two specialist moth species (Dichonia aprilina and Catocala sponsa) and two generalist species (Acronicta psi and Amphipyra pyramidea) to four artificial diets: a control diet, a diet with 50 mg g^?1 vescalagin, a diet with 15 mg/g condensed tannins, and a diet with both 50 mg g^?1 vescalagin and 15 mg g^?1 condensed tannins. Overall, we find drastic effects of vescalagin and pronounced differences in the responses of generalist and specialist herbivores, but no detectable effects of condensed tannins, and no interaction between the two types of compounds. More specifically, vescalagin reduced the growth of generalist species to one‐half of control levels over 72 h. The compound served as a strong feeding deterrent to generalists, reducing ingestion rates by two‐thirds. Vescalagin also reduced the metabolic and growth efficiency of generalist species to between 16% and 56% of control levels – effects which were lacking or even reversed in specialist species. These patterns suggest that vescalagin forms an important part of the oak's defence against herbivores, and that specialist species have adapted to deal with such substances. In terms of biological effects, condensed tannins seem much less important. Given a quantitative dominance of hydrolysable tannins over condensed tannins in oak leaves, and a seasonal decline in overall tannin levels, these findings contradict the previous notion that widespread spring feeding among oak herbivores could be attributed to tannins.     

Physiological effects of climate on distributions of endothermic species

Aim Determining the mechanisms underlying climatic limitation of species distributions is essential for understanding responses to current climatic change. Disentangling direct (e.g. physiological) and indirect (e.g. trophic) effects of climate on distributions through occurrence‐based modelling is problematic because most species use the same area for both shelter and food acquisition. By focusing on marine birds that breed on land but feed at sea, we exploit a rare opportunity to dissociate direct from indirect climatic effects on endothermic species. Location Coastal Europe. Methods We developed climate‐response surfaces (CRS) for 13 seabird species in coastal Europe, linking terrestrial climatic variables considered important for heat transfer with presence/absence data across each species’ entire European breeding range. Agreement between modelled and actual distribution was assessed for jackknifed samples using area under the curve (AUC) of receiver operating characteristic plots. Higher AUC values indicated closer correspondence between observed breeding distribution and terrestrial climate. We assessed the influence of several ecological factors on model performance across species. Results Species maximum foraging range and breeding latitude explained the greatest proportion of variation in AUC across species. AUC was positively related to both latitude and foraging range. Main conclusions The positive relationship between foraging range and AUC suggests that species foraging further are more likely to be constrained by environmental heat stress conditions at the breeding site. One plausible explanation is that long foraging trips result in one parent spending long periods in continuous nest attendance, exposed to such conditions. These may include negative impacts through predation and parasitism in addition to physiological responses to the thermal environment, which probably explains why our models performed better for species breeding at higher latitudes, where such species interactions are considered less important. These data highlight the importance of considering physiological impacts of climate for endothermic species, and suggest that widespread oceanographic changes that reduce prey quality and quantity for seabirds at sea may be exacerbated by additional impacts of climate at the breeding site.     

The plasticity of the germinative response in the populations of two xeric species inhabiting two contrasting environments of central Mexico

The species' germination response evolves based on its population environment; therefore, the responses of each local population evolve independently. We investigated two xeric species from central Mexico, Echeveria gibbiflora and Penstemon campanulatus, the populations of which inhabit two localities (Reserva Ecológica del Pedregal de San Ángel [REPSA] and Parque Ecológico de la Ciudad de México [PECM]) that differ in environmental conditions. For both species and populations, final germination, cardinal temperatures, thermal time and range of temperature for germination (RTG) were determined in seeds that were (a) collected recently, (b) stored in a laboratory for 2 months and (c) reciprocally buried in field conditions for 2 months. The results indicated that for both species, seed population, laboratory storage and temperature were significant for final germination. These responses indicated differences in germination based primarily on the site in P. campanulatus (PECM seeds germinated at higher percentages than REPSA seeds) and the burial site in the REPSA seeds of E. gibbiflora. Cluster and discriminant analyses were conducted for both species, identifying the following significant variables for group treatments: base temperature between the stored and buried seeds of E. gibbiflora and the ceiling temperature between the recently collected, stored and buried seeds of P. campanulatus. The results suggest that instead of seed population, burial (in both species) and laboratory storage (in P. campanulatus) narrowed the RTG. These responses could indicate plasticity in both germination and dormancy in response to environmental conditions experienced in the different habitats, which are crucial for understanding species' adaptive capacity.     

Cluster root formation and function vary in two species with contrasting geographic ranges

Plant and Soil - Southern South American Proteaceae can occupy soils that are rich in total phosphorus (P) but poor in available P (for example volcanic soils) thanks to their cluster roots (CR),...