Complex, dynamic combination of physical, chemical and nutritional variables controls spatio-temporal variation of sandy beach community structure

Sandy beach ecological theory states that physical features of the beach control macrobenthic community structure on all but the most dissipative beaches. However, few studies have simultaneously evaluated the relative importance of physical, chemical and biological factors as potential explanatory variables for meso-scale spatio-temporal patterns of intertidal community structure in these systems. Here, we investigate macroinfaunal community structure of a micro-tidal sandy beach that is located on an oligotrophic subtropical coast and is influenced by seasonal estuarine input. We repeatedly sampled biological and environmental variables at a series of beach transects arranged at increasing distances from the estuary mouth. Sampling took place over a period of five months, corresponding with the transition between the dry and wet season. This allowed assessment of biological-physical relationships across chemical and nutritional gradients associated with a range of estuarine inputs. Physical, chemical, and biological response variables, as well as measures of community structure, showed significant spatio-temporal patterns. In general, bivariate relationships between biological and environmental variables were rare and weak. However, multivariate correlation approaches identified a variety of environmental variables (i.e., sampling session, the C∶N ratio of particulate organic matter, dissolved inorganic nutrient concentrations, various size fractions of photopigment concentrations, salinity and, to a lesser extent, beach width and sediment kurtosis) that either alone or combined provided significant explanatory power for spatio-temporal patterns of macroinfaunal community structure. Overall, these results showed that the macrobenthic community on Mtunzini Beach was not structured primarily by physical factors, but instead by a complex and dynamic blend of nutritional, chemical and physical drivers. This emphasises the need to recognise ocean-exposed sandy beaches as functional ecosystems in their own right.     

Marine chemical ecology: what''s known and what''s next?

In this review, I summarize recent developments in marine chemical ecology and suggest additional studies that should be especially productive. Direct tests in both the field and laboratory show that secondary metabolites commonly function as defenses against consumers. However, some metabolites also diminish fouling, inhibit competitors or microbial pathogens, and serve as gamete attractants; these alternative functions are less thoroughly investigated. We know little about how consumers perceive secondary metabolites or how ecologically realistic doses of defensive metabolites affect consumer physiology or fitness, as opposed to feeding behavior. Secondary metabolites have direct consequences, but they do not act in isolation from other prey characteristics or from the physical and biological environment in which organisms interact with their natural enemies. This mandates that marine chemical ecology be better integrated into a broader and more complex framework that includes aspects of physiological, population, community, and even ecosystem ecology. Recent advances in this area involve assessing how chemically mediated interactions are affected by physical factors such as flow, desiccation, UV radiation, and nutrient availability, or by biological forces such as the palatability or defenses of neighbors, fouling organisms, or microbial symbionts. Chemical defenses can vary dramatically among geographic regions, habitats, individuals within a local habitat, and within different portions of the same individual. Factors affecting this variance are poorly known, but include physical stresses and induction due to previous attack. Studies are needed to assess which consumers induce prey defenses, how responses vary in environments with differing physical characteristics, and whether the ‘induced’ responses are a direct response to consumer attack or are a defense against microbial pathogens invading via feeding wounds. Although relatively unstudied, ontogenetic shifts in concentrations and types of defenses occur in marine species, and patterns of larval chemical defenses appear to provide insights into the evolution of complex life cycles and of differing modes of development among marine invertebrates. The chemical ecology of marine microbes is vastly underappreciated even though microbes produce metabolites that can have devastating indirect effects on non-target organisms (e.g., red tide related fish kills) and significantly affect entire ecosystems. The natural functions of these metabolites are poorly understood, but they appear to deter both consumers and other microbes. Additionally, marine macro-organisms use metabolites from microbial symbionts to deter consumers, subdue prey, and defend their embryos from pathogens. Microbial chemical ecology offers unlimited possibilities for investigators that develop rigorous and more ecologically relevant approaches.     

Phylogenetic Age is Positively Correlated with Sensitivity to Timber Harvest in Bornean Mammals

The reasons that forest vertebrates differ in their response to selective timber extraction in tropical forests remain poorly characterized. Understanding what determines response and sensitivity can indicate how forest management might yield greater conservation benefits, and help us identify which lesser-known species may be especially vulnerable. We assessed the response of 41 Bornean mammals to selective timber harvest and tested eight hypotheses regarding the correlation between those responses and a range of species characteristics. Multivariate analyses show that phylogenetic species age is a key variable determining sensitivity. Older species are less able to cope with the effects of selective timber harvest. Most of these species are endemic to insular southeast Asia, and do not occur on the Asian mainland. These species are more specialized, and appear less able to cope with habitat change. In contrast, species tolerant to logging evolved more recently. This group tends to be omnivorous or herbivorous, to use all vegetation strata, and to be regionally widespread. This finding allows the sensitivity to habitat disturbance of lesser-known species to be predicted, and therefore has important conservation implications. These new insights also help in the design of large-scale forest landscapes that combine sustainable forest management and species conservation requirements. We recognize that these functions can be compatible, but that some species still need completely protected areas for their survival.     

Latitudinal Patterns of Herbivory in Mangrove Forests: Consequences of Nutrient Over-Enrichment

Ecosystems in the tropics are predicted to have stronger responses to nutrient enrichment, greater diversity, and more intense biotic interactions than in temperate areas. Mangrove forests, which occur across a broad biogeographic range from warm temperate to tropical, provide a unique opportunity to test these hypotheses by investigating the responses of herbivores to nutrient enrichment in temperate versus tropical latitudes. Mangroves are complex intertidal ecosystems with spatial differences in structure and diversity along tidal gradients and are threatened globally by human activities including nutrient over-enrichment. In this study, we used long-term fertilization experiments at the Indian River Lagoon, FL; Twin Cays, Belize; and Bocas del Toro, Panamá to determine how increased nutrients impact herbivore abundance and herbivory of Rhizophora mangle at the tree, forest, and regional scales. At these locations, which span approximately 2185 km and 18.4º of latitude, we fertilized individual trees with one of three treatments (Control, +N, +P) in two zones (fringe, scrub) along transects perpendicular to the shoreline and measured their responses for 4 years. Herbivory was measured as folivory, loss of yield, and tissue mining. Although nutrient enrichment altered plant growth, leaf traits, and nutrient dynamics, these variables had little effect on folivory at any location. Our results did not support the prediction that herbivory and per capita consumption are greatest at the most tropical location. Instead, folivory was highest at the most temperate location and lowest at the intermediate location. Folivory was generally higher in the fringe than in the scrub zone, but the pattern varied by location, herbivore, and nutrient treatment. Folivory by a dominant herbivore, Aratus pisonii, decreased from the highest to the lowest latitude. Our data suggest that factors controlling population dynamics of A. pisonii cascade to the mangrove canopy, linking herbivory to crab densities.     

Altitudinal replacement of Ephemeroptera in a subtropical river

An altitudinal sampling transect was established in a subtropical mountain river to determine if replacement between two mayfly faunal components (oligostenothermal and polystenothermal) occurred. We detected three main groups: Group A, species with high abundance at higher stations, declining abruptly downstream; Group B, species with maximum abundance at lower elevations; either declining abruptly upstream or absent from higher elevations; and Group C, species with little elevational change. The physical and chemical variables did not change abruptly with altitude during our winter sampling, although the distribution of groups A and B species did. The observed distributional patterns of groups A and B do not appear to be correlated with variations in the physical and chemical variables surveyed.     

Androgen receptor gene sequence and basal cortisol concentrations predict men's hormonal responses to potential mates

Exposure to potential mates triggers rapid elevations of testosterone and glucocorticoid concentrations in males of many non-human species, and preliminary studies support similar effects in human males. The human studies have all reported large individual differences in these responses, however, and the present study tested whether specific biological variables may help explain these differences. Replicating past research, the present study found that men''s salivary testosterone and cortisol concentrations increased after a brief conversation with a young woman, but did not change (or slightly decreased) after a conversation with a young man. In addition, smaller numbers of CAG repeats in men''s androgen receptor gene, and lower baseline cortisol concentrations, each predicted larger testosterone responses to the interactions with women. The CAG repeat finding demonstrates that a specific genetic polymorphism predicts physiological responses to social interactions that may in turn have important downstream consequences on men''s mating behaviour. The effects of cortisol are consistent with past demonstrations of glucocorticoid inhibition of testosterone production and show that such inhibition also affects testosterone responses to social stimuli. In sum, the present study both confirms men''s hormonal reactions to potential mates and identifies novel biological variables that predict individual differences in these responses.     

Coupling of autotrophic and heterotrophic processes in a Baltic estuarine mixing gradient (Pomeranian Bight)

This paper presents the results of a long-term survey of the hydrography, nutrients and phytoplankton in Tolo Harbour carried out between 1982 and 1992. Some nutrients such as total inorganic nitrogen, ammonia and total phosphorus increased during the 10 year period, but chlorophyll a, which indicated algal biomass, did not show an increasing trend. The phytoplankton of Tolo Harbour consisted largely of diatoms. Dinoflagellates and minor algal groups such as cryptomonads and small flagellates constituted a smaller fraction of the phytoplankton population. Densities of diatoms and minor algal groups increased in some stations, but the density of dinoflagellates remained relatively unchanged during the study period. Most nutrient variables were negatively correlated with densities of diatom and total phytoplankton, and positively correlated with densities of minor algal groups. While dinoflagellate densities were positively correlated with total nitrogen in some stations, no correlation existed between dinoflagellate density and most of the nutrient variables. Our results show that there is a gradual change in phytoplankton community in Tolo Harbour,most notably in the nutrient-rich inner harbour waters, with the smaller algae assuming increasing abundance. Thus there was a net increase in density of total phytoplankton even though chlorophyll a concentrations did not increase. No evidence was found in this study to show that increased nutrient loading would inevitably lead to increase in densities of dinoflagellates in Tolo Harbour. Instead, dinoflagellate densities showed stronger correlations with physical variables such as temperature, pH and salinity. This revised version was published online in August 2006 with corrections to the Cover Date.     

Linking forest harvest and landscape factors to benthic macroinvertebrate communities in the interior of British Columbia

Detecting the magnitude of human-induced disturbance events, such as forest harvest, on biological communities is often confounded by other environmental gradients and scales at which these effects are examined. In this study, benthic invertebrates were collected from 43 streams across four basins and two geographic regions to (1) determine whether invertebrate abundance and community structure are best explained by historic forest harvest, landscape variables or a combination of both, and (2) evaluate associations among harvest, landscape variables, in-stream physical habitat, and invertebrates. Nonmetric multidimensional scaling showed that invertebrate community structure was primarily explained by watershed area and elevation, and basin and region but not by measures of forest harvest. Model selection using an information-theoretic approach and Akaike’s information criterion indicated that watershed area was the most important variable explaining clinger and long-lived taxa richness, while basin was the most important variable explaining total abundance, and total, Ephemeroptera, Plecoptera, and Trichoptera taxa richness. Forest harvest ranked lower than landscape variables in relative importance in all models. These results suggest that landscape characteristics were relatively more important in predicting invertebrate community structure than forest harvest, and should therefore be considered when assessing the impacts of both reach and watershed scale forest harvest on benthic communities. Perhaps, the levels of forest harvest examined in this study had only marginal effects on benthic invertebrates because these ecosystems are naturally resilient as a result of frequent disturbance from forest fires.     

Clustering Timber Harvests and the Effect of Dynamic Forest Management Policy on Forest Fragmentation

To integrate multiple uses (mature forest and commodity production) better on forested lands, timber management strategies that cluster harvests have been proposed. One such approach clusters harvest activity in space and time, and rotates timber production zones across the landscape with a long temporal period (dynamic zoning). Dynamic zoning has been shown to increase timber production and reduce forest fragmentation by segregating uses in time without reducing the spatial extent of timber production. It is reasonable to wonder what the effect of periodic interruptions in the implementation of such as strategy might be, as would be expected in a dynamic political environment. To answer these questions, I used a timber harvest simulation model (HARVEST) to simulate a dynamic zoning harvest strategy that was periodically interrupted by changes in the spatial dispersion of harvests, by changes in timber production levels, or both. The temporal scale (period) of these interruptions had impacts related to the rate at which the forest achieved canopy closure after harvest. Spatial dynamics in harvest policies had a greater effect on the amount of forest interior and edge than did dynamics in harvest intensity. The periodically clustered scenarios always produced greater amounts of forest interior and less forest edge than did their never clustered counterparts. The results suggest that clustering of harvests produces less forest fragmentation than dispersed cutting alternatives, even in the face of a dynamic policy future. Although periodic episodes of dispersed cutting increased fragmentation, average and maximum fragmentation measures were less than if clustered harvest strategies were never implemented. Clustering may also be useful to mitigate the fragmentation effects of socially mandated increases in timber harvest levels. Implementation of spatial clustering during periods of high timber harvest rates reduced the variation in forest interior and edge through time, providing a more stable supply of forest interior habitat across the landscape. Received 19 September 1997; accepted 6 August 1998.     

Interactions of Physical,Chemical and Biological Processes in Depth and Time within a Productive English Lake during Summer Stratification

A survey is given of physical, chemical and biological events in the water-mass of a productive lake (Esthwaite Water, N. England) during summer stratification. They are interrelated in terms of i) responses to meteorological changes (ii) susceptibility to density stratification (iii) participation in acid-base and redox systems, with interactions of these (iv) modification due to the generation of particulate material from soluble precursors (v) limiting factors in such bio-generation (vi) mechanisms of internal nutrient loading, and (vii) control by the characteristics of individual plankters. The significance is demonstrated of differential inputs of meteorological variables, and especially of biological production and degradation, for determining the overall structure and metabolism of the lake.     

Cellulose microfibril angle in the cell wall of wood fibres

The term microfibril angle (MFA) in wood science refers to the angle between the direction of the helical windings of cellulose microfibrils in the secondary cell wall of fibres and tracheids and the long axis of cell. Technologically, it is usually applied to the orientation of cellulose microfibrils in the S2 layer that makes up the greatest proportion of the wall thickness, since it is this which most affects the physical properties of wood. This review describes the organisation of the cellulose component of the secondary wall of fibres and tracheids and the various methods that have been used for the measurement of MFA. It considers the variation of MFA within the tree and the biological reason for the large differences found between juvenile (or core) wood and mature (or outer) wood. The ability of the tree to vary MFA in response to environmental stress, particularly in reaction wood, is also described. Differences in MFA have a profound effect on the properties of wood, in particular its stiffness. The large MFA in juvenile wood confers low stiffness and gives the sapling the flexibility it needs to survive high winds without breaking. It also means, however, that timber containing a high proportion of juvenile wood is unsuitable for use as high-grade structural timber. This fact has taken on increasing importance in view of the trend in forestry towards short rotation cropping of fast grown species. These trees at harvest may contain 50% or more of timber with low stiffness and therefore, low economic value. Although they are presently grown mainly for pulp, pressure for increased timber production means that ways will be sought to improve the quality of their timber by reducing juvenile wood MFA. The mechanism by which the orientation of microfibril deposition is controlled is still a matter of debate. However, the application of molecular techniques is likely to enable modification of this process. The extent to which these techniques should be used to improve timber quality by reducing MFA in juvenile wood is, however, uncertain, since care must be taken to avoid compromising the safety of the tree.     

Do non-native earthworms in Southeast Alaska use streams as invasional corridors in watersheds harvested for timber?

Exotic earthworms from Europe and Asia have invaded previously earthworm-free areas of North America where they consume leaf litter, mix soil horizons, and alter nutrient cycling. Primarily, earthworm introductions occur through human activities; we hypothesized that the combination of logging (i.e., road construction and soil disturbance) and stream transport (i.e., hydrochory) allows earthworms to invade new ecosystems and spread within watersheds. On Prince of Wales Island, AK, we surveyed riparian zones in 11 watersheds with varying timber harvest intensity for terrestrial oligochaetes. Additionally, common invasive earthworms were experimentally submerged in a local stream to test for tolerance to prolonged immersion: all taxa survived immersion for at least 6 days. Using principal components analysis, watershed and harvest variables describing the watersheds upstream of our sampled riparian areas were reduced to two principal components describing harvest intensity (PC1) and harvest style (PC2). Logistic models successfully predicted earthworm abundance (r ²  = 0.70) from PC1, which indicated that watersheds with older, intense upstream timber harvest contained larger earthworm populations. Earthworm species richness was best predicted by PC2 (r ²  = 0.39), which suggested that earthworm communities in watersheds containing large clear-cut stands were more species-rich. Collectively, these results suggest that (1) invasive earthworms may use streams for dispersal and (2) upstream introductions via timber harvest can initiate downstream earthworm invasions. Hydrochory would allow invasive earthworms to spread at rates (tens of km d⁻¹) that are much greater than previously reported rates of terrestrial spread (5–10 m y⁻¹). Effective control of exotic earthworms in riparian zones will require watershed-level management and surveillance.     

择伐对动物多样性的影响

择伐是生态林业持续利用的一种途径 ,即以达到在经济上是可持续的 ,保持稳定的木材产量 ,同时保护生物多样性。择伐对动物多样性的影响成为生物多样性保护和生态林业持续性研究的一个焦点。择伐因不同地区和不同森林类型以及择伐木的树种、大小、生长状况、分布格局、择伐的强度等不同 ,对不同动物类群的影响可能不同。大多数研究认为 ,在采伐迹地中 ,分布范围广或广适应种的物种多样性或丰富度将增加 ,而适应于原始林的专化种或狭生种的物种多样性或丰富度将下降。在自然干扰频繁的地区 ,择伐对动物多样性影响相对较小。在热带原始林 ,动物多样性受择伐影响大 ,而在温带森林 ,动物多样性受影响小。轻度的择伐对动物多样性影响小 ,因而与生物多样性保护相协调。采伐时 ,动物的食物树种、枯死木和为动物提供洞穴的树应得到保护。大多数研究仅比较了择伐对动物多样性的影响 ,而对择伐对动物多样性影响的生态学机制探讨较少。我国这方面开展的研究较少。未来的研究重点包括了解择伐对动物多样性影响的生态学机理、择伐对动物遗传多样性、生态系统过程、非指示类群的影响以及枯死木的生态功能。     

Assessment of river health: accounting for perturbation pathways in physical and ecological space

1. A full understanding of changes to river ecosystem structure and functioning along the continuum from relatively pristine to profoundly perturbed requires knowledge of physical, chemical and ecological properties at many spatial and temporal scales. Perturbations may span broad spatio-temporal scales or be spatially and temporally discrete. 2. The relevant scale for study depends on the manner in which perturbations move through two kinds of pathways – through the physical space of the catchment hierarchy and through the ecological space of river food webs. Different kinds of perturbation (e.g. inputs of sediment, nitrogen or phosphorus, changes to shading or discharge) vary in the degree and manner in which they are propagated downstream and through food webs. 3. The fundamental importance of disturbance regimes and refugia to river health is now clear and managers need to take this into account when devising river management schemes. 4. A comparison of the physics, chemistry and ecology of streams in catchments of native tussock and exotic pasture grassland in New Zealand serves to emphasize (i) the extreme complexity of interacting factors resulting from land use change, (ii) the importance of disturbance regime (not encapsulated in biotic indices) and biogeographic patterns (usually unmeasured) in determining ecosystem structure and functioning, and (iii) the lack of concordance between any single index of health and various fundamental features of ecosystem functioning. 5. Practical considerations limit most evaluations of river health to a small suite of indices, though it is important that researchers continue to evaluate the spatial, temporal and biological limitations of these indices. The vagaries of history and geography (extinction and colonization trajectories in relation to natural disturbance regimes) and the complexity of interacting physical, chemical and ecological responses to perturbation suggest that multi-scale, multi-temporal studies of river function offer the best opportunity to evaluate river health.     

Plant allocation of carbon to defense as a function of herbivory,light and nutrient availability

We use modeling to determine the optimal relative plant carbon allocations between foliage, fine roots, anti-herbivore defense, and reproduction to maximize reproductive output. The model treats these plant components and the herbivore compartment as variables. Herbivory is assumed to be purely folivory. Key external factors include nutrient availability, degree of shading, and intensity of herbivory. Three alternative functional responses are used for herbivory, two of which are variations on donor-dependent herbivore (models 1a and 1b) and one of which is a Lotka–Volterra type of interaction (model 2). All three were modified to include the negative effect of chemical defenses on the herbivore. Analysis showed that, for all three models, two stable equilibria could occur, which differs from most common functional responses when no plant defense component is included. Optimal strategies of carbon allocation were defined as the maximum biomass of reproductive propagules produced per unit time, and found to vary with changes in external factors. Increased intensity of herbivory always led to an increase in the fractional allocation of carbon to defense. Decreases in available limiting nutrient generally led to increasing importance of defense. Decreases in available light had little effect on defense but led to increased allocation to foliage. Decreases in limiting nutrient and available light led to decreases in allocation to reproduction in models 1a and 1b but not model 2. Increases in allocation to plant defense were usually accompanied by shifts in carbon allocation away from fine roots, possibly because higher plant defense reduced the loss of nutrients to herbivory.     

A slow opportunist: physiological and growth responses of an obligate understory plant to patch cut harvesting

Understory light environments change rapidly following timber harvest, and while many understory species utilize and benefit from the additional light, this response is not ubiquitous in shade-obligate species. I examined the effects of patch cut timber harvest on the physiology and growth of an obligate forest understory species to determine if disturbances via timber harvest are physiological stressors or whether such disturbances provide physiological benefits and growth increases in understory species. Forest canopy structure, along with photosynthesis, respiration, water use efficiency, stomatal conductance, and growth rates of American ginseng were quantified one summer before and two summers after patch cut timber harvest. Survival following timber harvest was lower than that observed at undisturbed populations; however, growth of survivors increased post-harvesting, with growth increasing as a function of canopy openness. Light response curves as well as photosynthesis and respiration rates indicated that plants were not well acclimated to higher light levels in the growing season after timber harvest, but rather to two growing seasons after harvest. Relative growth rate formed a positive linear relationship with maximum photosynthesis following timber harvest. My study suggests that ginseng is a “slow opportunist”, because while it benefits from sudden light increases, acclimation lags at least one growing season behind canopy changes. American ginseng is surprisingly resilient in the face of a discrete environmental shift and may benefit from forest management strategies that mimic the natural disturbance regimes common in mature forests throughout its range.     

Atmospheric CO(2) and mycorrhiza effects on biomass allocation and nutrient uptake of nodulated pea (Pisum sativum L.) plants

The effect of ambient and elevated atmospheric CO(2) on biomass partitioning and nutrient uptake of mycorrhizal and non-mycorrhizal pea plants grown in pots in a controlled environment was studied. The hypothesis tested was that mycorrhizae would increase C assimilation by increasing photosynthetic rates and reduce below-ground biomass allocation by improving nutrient uptake. This effect was expected to be more pronounced at elevated CO(2) where plant C supply and nutrient demand would be increased. The results showed that mycorrhizae did not interact with atmospheric CO(2) concentration in the variables measured. Mycorrhizae did not affect photosynthetic rates, had no effect on root weight or root length density and almost no effect on nutrient uptake, but still significantly increased shoot weight and reduced root/shoot ratio at harvest. Elevated CO(2) increased photosynthetic rates with no evidence for down-regulation, increased shoot weight and nutrient uptake, had no effect on root weight, and actually reduced root/shoot ratio at harvest. Non-mycorrhizal plants growing at both CO(2) concentrations had lower shoot weight than mycorrhizal plants with similar nutritional status and photosynthetic rates. It is suggested that the positive effect of mycorrhizal inoculation was caused by an enhanced C supply and C use in mycorrhizal plants than in non-mycorrhizal plants. The results indicate that plant growth was not limited by mineral nutrients, but partially source and sink limited for carbon. Mycorrhizal inoculation and elevated CO(2) might have removed such limitations and their effects on above-ground biomass were independent, positive and additive.     

Genotypic variation in response of quaking aspen (Populus tremuloides) to atmospheric CO2 enrichment

Enriched atmospheric CO₂ alters the quantity and quality of plant production, but how such effects vary among plant genotypes is poorly known. We evaluated the independent and interactive effects of CO₂ and nutrient availability on growth, allocation and phytochemistry of six aspen (Populus tremuloides Michx.) genotypes. One-year-old trees, propagated from root cuttings, were grown in CO₂-controlled glasshouses for 64 days, then harvested. Foliage was analyzed for levels of water, nitrogen, starch, phenolic glycosides and condensed tannins. Of seven plant growth/allocation variables measured, four (biomass production, stem growth, relative growth rate and root:shoot ratio) exhibited marginally to highly significant CO₂ 2 genotype interactions. CO₂ enrichment stimulated growth of some genotypes more than others, and this interaction was itself influenced by soil nutrient availability. In addition, enriched CO₂ increased the magnitude of the among-genotype variance for four of the growth/allocation variables. Of six foliar chemical constituents analyzed, CO₂-mediated responses of two (the phenolic glycoside tremulacin and condensed tannins) varied among genotypes. Moreover, enriched CO₂ increased the magnitude of among-genotype variance for four of the chemical variables. Given the importance of these growth and chemical characteristics to the biological fitness of aspen, this research suggests that projected atmospheric CO₂ increases are likely to alter the genetic structures and evolutionary trajectories of aspen populations.     

Small-scale spatial heterogeneity in the vertical distribution of soil nutrients has limited effects on the growth and development of Prosopis glandulosa seedlings

We examined the above- and below-ground responses of seedlings of the woody shrub Prosopis glandulosa to the spatial heterogeneity of soil nutrients within the root zone. We performed a microcosm experiment where seedlings were grown with different combinations of nutrients [nitrogen (N), phosphorus (P), and both combined (NP)] and under different levels of nutrient heterogeneity (nutrients supplied as patches located in the bottom and/or upper portion of rooting zone versus homogeneous distribution). Seedling morphology and biomass did not show a strong response to changes in nutrient ion or spatial heterogeneity. Height, number of leaves, and specific leaf area did not vary significantly between treatments. The number of leaves, foliar biomass, stem biomass and biomass allocation to stems of seedlings showed more responsiveness to the addition of N and NP than to the addition of P. The spatial heterogeneity of nutrients affected the diameter, root biomass and leaf N content. Seedlings had higher diameter and root biomass when the nutrients were homogeneously distributed as compared to their placement as patches in the bottom of the microcosms. Their leaf N concentration increased in those treatments where the nutrient patch was located in the lower half as compared to the upper half of the microcosms. Root foraging responses to nutrient patches varied with their location. Significant root proliferation was observed when patches of N, P and NP were located in the upper portion of the rooting zone; when they were located in the lower portion such a response was observed only for P. Despite our findings that Prosopis seedlings have a low overall responsiveness to small-scale vertical differences in soil nutrient heterogeneity, our results suggest that these differences may modify the growth dynamics of the secondary roots of this ecologically important dryland species during the early stages of its development.     

Effects of timber harvest on phlebotomine sand flies (Diptera: Psychodidae) in a production forest: abundance of species on tree trunks and prevalence of trypanosomatids

The Amazon forest is being exploited for timber production. The harvest removes trees, used by sand flies as resting sites, and decreases the canopy, used as refuges by some hosts. The present study evaluated the impact of the timber harvest, the abundance of sand flies, and their trypanosomatid infection rates before and after selective logging. The study was accomplished in terra-firme production forest in an area of timber harvest, state of Amazonas, Brazil. Sand fly catches were carried out in three areas: one before and after the timber harvest, and two control areas, a nature preservation area and a previously exploited area. The flies were caught by aspiration on tree trunks. Samples of sand flies were dissected for parasitological examination. In the site that suffered a harvest, a larger number of individuals was caught before the selective extraction of timber, showing significant difference in relation to the number of individuals and their flagellate infection rates after the logging. The other two areas did not show differences among their sand fly populations. This fact is suggestive of a fauna sensitive to the environmental alterations associated with selective logging.