RELATIONSHIP BETWEEN SELF-FERTILITY,ALLOCATION OF GROWTH,AND INBREEDING DEPRESSION IN THREE CONIFEROUS SPECIES

Mortality and growth of self and outcross families of three wind-pollinated, mixed-mating, long-lived conifers, Douglas-fir (Pseudotsuga menziesii), ponderosa pine (Pinus ponderosa), and noble fir (Abies procera) were followed from outplanting to age 26 (25 for noble fir) in spaced plantings at a common test site. Response to inbreeding differed greatly among species over time and in all regards. Only Douglas-fir and noble fir will be contrasted here, because ponderosa pine usually was intermediate to the other two in its response to inbreeding. In earlier reports, compared to noble fir Douglas-fir had a higher rate of primary selfing and larger inbreeding depression in seed set. Douglas-fir continued to have higher inbreeding depression in nursery and early field survival. The species differed in time courses of inbreeding depression in height and in allocation of growth due to crowding. Between ages 6 and 12, the relative elongation rate (dm · dm^?1 · yr^?1) of Douglas-fir was significantly greater in the selfs than in the outcrosses. The response was not observed in noble fir. At final measurement, inbreeding depression in diameter relative to inbreeding depression in height was greater in Douglas-fir than in noble fir. At final measurement inbreeding depression in height was inversely related to inbreeding depression in survival. Cumulative inbreeding depressions from time of fertilization to final measurement were 0.98, 0.94, and 0.83 for Douglas-fir, ponderosa pine, and noble fir, respectively, which indicates that selfs will not contribute to the mature, reproductive populations.     

Long-Term Ecosystem Effects of Sand-Binding Vegetation in the Tengger Desert, Northern China

The planting of sand‐binding vegetation in the Shapotou region at the southeastern edge of the Tengger Desert began in 1956. Over the past 46 years, it has not only insured the smooth operation of the Baotou–Lanzhou railway in the sand dune section but has also played an important role in the restoration of the local eco‐environment; therefore, it is viewed as a successful model for desertification control and ecological restoration along the transport line in the arid desert region of China. Long‐term monitoring and focused research show that within 4–5 years of establishment of sand‐binding vegetation, the physical surface structure of the sand dunes stabilized, and inorganic soil crusts formed by atmospheric dust gradually turned into microbiotic crusts. Among the organisms comprising these crusts are cryptogams such as desert algae and mosses. In the 46 years since establishing sand‐binding vegetation, some 24 algal species occurred in the crusts. However, only five moss species were identified, which was fewer than the species number in the crust of naturally fixed sand dunes. Other results of the planting were that near‐surface wind velocity in the 46‐year‐old vegetation area was reduced by 54.2% compared with that in the moving sand area; soil organic matter increased from 0.06% in moving sand dunes to 1.34% in the 46‐year‐old vegetation area; the main nutrients N, P, K, etc., in the desert ecosystem increased; soil physicochemical properties improved; and soil‐forming processes occurred in the dune surface layer. Overall, establishment of sand‐binding vegetation significantly impacted soil water cycles, creating favorable conditions for colonization by many herbaceous species. These herbaceous species, in turn, facilitated the colonization and persistence of birds, insects, soil animals, and desert animals. Forty‐six years later, some 28 bird species and 50 insect species were identified in the vegetated dune field. Thus, establishment of a relatively simple community of sand‐binding species led to the transformation of the relatively barren dune environment into a desert ecosystem with complex structure, composition, and function. This restoration effort shows the potential for short‐term manipulation of environmental variables (i.e., plant cover via artificial vegetation establishment) to begin the long‐term process of ecological restoration, particularly in arid climates, and demonstrates several techniques that can be used to scientifically monitor progress in large‐scale restoration projects.     

Thermal influences on temporal changes in plasma testosterone and oestradiol-17β concentrations during gonadal recrudescence in female common wolffish

Temperature treatment during ovarian recrudescence influenced temporal changes in plasma testosterone (T) and oestradiol-17β (E₂). In fish exposed to 8 and 12° C early in the cycle the peaks of both T and E₂ were delayed by 4 weeks in comparison with those of fish held at 4° C throughout the experiment. These differences were accompanied by corresponding shifts in the timing of ovulation.     

Structuring features of lake districts: landscape controls on lake chemical responses to drought

1. Within a lake district of relatively homogeneous geomorphology, the responses of lakes to climate are influenced by the complexity of the hydrogeologic setting, position in the landscape, and lake‐specific biological and physical features. We examined lake chemical responses to drought in surface water‐ and groundwater‐dominated districts to address two general questions. (1) Are spatial patterns in chemical dynamics among lakes uniform and synchronous within a lake district, suggesting broad geomorphic controls; variable in a spatially explicit pattern, with synchrony related to landscape position, suggesting hydrologic flowpath controls; or spatially unstructured and asynchronous, suggesting overriding control by lake‐specific factors? (2) Are lake responses to drought a simple function of precipitation quantity or are they dictated by more complex interactions among climate, unique lake features, and hydrologic setting? 2. Annual open‐water means for epilimnetic concentrations of chloride, calcium, sulfate, ANC, DOC, total nitrogen, silica, total phosphorus, and chlorophyll a measured between 1982 and 1995 were assembled for lakes in the Red Lake and ELA districts of north‐western Ontario, the Muskoka – Dorset district in south‐central Ontario, and the Northern Highland district of Wisconsin. Within each district, we compared responses of lakes classified by landscape position into highland or lowland, depending on relative location within the local to regional hydrologic flow system. Synchrony, defined as a measure of the similarity in inter‐annual dynamics among lakes within a district, was quantified as the Pearson product‐moment correlation (r) between two lakes with observations paired by year. To determine if solute concentrations were directly related to interannual variations in precipitation quantity, we used regression analysis to fit district‐wide slopes describing the relationship between each chemical variable and annual (June to May) and October to May (Oct–May) precipitation. 3. Among lakes in each of the three Ontario districts, the pattern of chemical response to interannual shifts in precipitation was spatially uniform. In these surface water‐ dominated districts, solute concentrations were generally a simple function of precipitation. Conservative solutes, like calcium and chloride, tended to be more synchronous and were negatively related to precipitation. Solutes such as silica, total phosphorus, and chlorophyll a, which are influenced by in‐lake processes, were less synchronous and relationships with precipitation tended to be positive or absent. 4. In the groundwater‐dominated Northern Highland lakes of Wisconsin, we observed spatial structure in drought response, with lowland lakes more synchronous than highland lakes. However, there was no evidence for a direct relationship between any solute and precipitation. Instead, increases in the concentration of the conservative ion calcium during drought were not followed by a symmetrical return to pre‐drought conditions when precipitation returned to normal or above‐average values. 5. For calcium, time lags in recovery from drought appeared related to hydrologic features in a complex way. In the highland Crystal Lake, calcium concentrations tracked lake stage inversely, with a return to pre‐drought concentrations and lake stage five years after the drought. This pattern suggests strong evaporative controls. In contrast, after five years of normal precipitation, calcium in the lowland Sparkling Lake had not returned to pre‐drought conditions despite a rebound in lake stage. This result suggests that calcium concentrations in lowland lakes were controlled more by regional groundwater flowpaths, which track climatic signals more slowly. 6. Temporal dynamics driven by climate were most similar among lakes in districts that have a relatively simple hydrology, such as ELA. Where hydrologic setting was more complex, as in the groundwater‐dominated Northern Highland of Wisconsin, the expression of climate signals in lakes showed lags and spatial patterns related to landscape position. In general, we expect that landscape and lake‐specific factors become increasingly important in lake districts with more heterogeneous hydrogeology, topography or land use. These strong chemical responses to climate need to be considered when interpreting the responses of lakes to other regional disturbances.     

Adverse ffects of covert iridovirus infection on life history and demographic parameters of Aedes aegypti

Abstract Sublethal viral infections can cause changes in the body size and demography of insect vectors, with important consequences for population dynamics and the probability that individual mosquitoes will transmit disease. This study examined the effects of covert (sublethal) infection by Invertebrate iridescent virus 6 (IIV‐6) on the demography of female Aedes aegypti and the relationship between key life history parameters in covertly infected female insects compared with healthy (control) insects or non‐infected mosquitoes that had survived exposure to virus inoculum without becoming infected. Of the female mosquitoes that emerged following exposure to virus inoculum and were offered blood meals, 29% (43/150) proved positive for covert IIV‐6 infection. The net reproductive rate (R₀) of covertly infected females was 50% lower for infected females compared to control mosquitoes, whereas non‐infected exposed females had an R₀ approximately 15% lower than that of controls. Reproduction caused a significant decrease of about 13 days in mosquito longevity compared to females that did not reproduce (P < 0.001). Infected females lived 5–8 days less than non‐infected exposed females or controls, respectively (P = 0.028). Infected females and non‐infected exposed females both had significantly shorter wings than control insects (P < 0.001). There was a significant positive correlation between wing length and longevity in covertly infected female mosquitoes but not in control or non‐infected exposed mosquitoes. Longer lived females produced more eggs in all treatments. There were no significant correlations between body size and fecundity or the production of offspring. There was also no correlation between fecundity and fertility, suggesting that sperm inactivation was a more likely cause of decreased fertility in older mosquitoes than sperm depletion. We conclude that covert infection by iridescent virus is likely to reduce the vectorial capacity of this mosquito.     

Anion exchange in the giant erythrocytes of African lungfish

Carbon dioxide transport in African lungfish Protopterus aethiopicus blood conformed to the typical vertebrate scheme, implying a crucial and rate-limiting role of erythrocyte Cl^–/HCO₃^– exchange. The rate coefficient for unidirectional Cl^– efflux via the anion exchanger ( k , s⁻¹) increased with temperature in African lungfish, but values were well below those reported in other species. The erythrocytes of African lungfish were, however, very large (mean cellular volume = 6940 µm³), and the ratio of cell water volume to membrane surface area was high ( V _w A _m⁻¹ = 1·89). Hence, the apparent Cl^– permeability ( P _Cl =  kV _w A _m⁻¹, µm s⁻¹) was close to that in other vertebrates. The plot of ln P _Cl against the inverse absolute temperature was left-shifted in the tropical African lungfish compared to the temperate rainbow trout Oncorhynchus mykiss , which supports the idea that P _Cl is similar among animals when compared at their preferred temperatures. Also, Q ₁₀ for anion exchange calculated from P _Cl values in African lungfish was 2·0, supporting the idea that the temperature sensitivity of erythrocyte anion exchange matches the temperature sensitivity of CO₂ production and transport in ectothermic vertebrates.     

Influence of Edge Exposure on Tree Seedling Species Recruitment in Tropical Rain Forest Fragments1

Edge creation has a pronounced influence on the understory vegetation, but the effects of edges on seedling species recruitment are still poorly understood. In Central Amazonia, 9–19 years after fragmentation, we recorded species richness and net seedling recruitment rate in 1 ha blocks exposed to none, one, or multiple edges within forest fragments. One‐hectare blocks were located in the center (no edge), the edge (one edge), the corners (two edges) of 10 and 100 ha fragments, and in a 1 ha fragment (four edges). In 1991, we counted all tree seedlings 5–100 cm tall found within permanent 1 m² plots located within the 1 ha blocks. In May 1993, we manually removed all seedlings that were smaller than 1 m tall from the permanent plots. Six years and five months later (October 1999), all new seedlings recruited into the plots were counted and classified into distinct morphospecies. Species richness of recruited seedlings, scaled by total seedling density, declined from the center to the edge, the corner blocks, and then to the 1 ha fragment. Overall, the four‐edged, 1 ha fragment had the poorest species richness and the non‐edged 100 ha central block the highest. The total number of recruited individuals was 40 percent less than that previously present, with the 100 ha corner having the lowest recruitment. Pairwise comparisons showed that species similarity was related to edge number for the 100 and 1 ha fragments. Species rank/abundance curves showed that a subset of species was common in all blocks within the fragments, and that the 100 ha center held more rare species than any other 1 ha block. This study demonstrated that, in a given fragment patch, the number of tree seedling species recruited varied inversely with the number of edges.     

The application of fourier transform infrared transmission spectroscopy to the study of model and natural membranes

Fourier transform infrared transmission spectroscopy is presented as a technique with great potential for the study of aqueous membrane preparations. The methodology of sample preparation, spectra recording and data reduction is outlined. Spectral parameters are derived from FT-IR difference spectra which provide an extremely sensitive means to monitor the temperature-dependent behavior of individual vibrational modes in model and natural membranes.     

Niche properties of Central European spiders: shading, moisture and the evolution of the habitat niche

Aim  Niche theory emphasizes the importance of environmental conditions for the distribution and abundance of species. Using a macroecological approach our study aimed at identifying the important environmental gradients for spiders. We generated numerical values of niche position and niche width. We also investigated relationships between these niche properties as well as the degree of phylogenetic conservatism in order to draw conclusions about the evolution of the habitat niche.
Location  Central Europe: lowlands of Austria, Belgium, Germany, Luxembourg, the Netherlands and Switzerland.
Methods  We analysed 244 published spider communities from 70 habitat types by correspondence analysis. The resulting community scores were used to test for correlations with habitat characteristics. Species scores were used to derive niche position (mean scores) and niche width (standard deviation of scores). To test for niche conservatism we estimated variance components across the taxonomic hierarchy.
Results  The first two axes of the correspondence analysis were correlated with shading and moisture, respectively. Niche width had a hump-shaped relationship to both environmental gradients. β-diversity was strikingly higher in open habitats than in forests. Habitat niche conservatism was lower than phylogenetic conservatism in body size.
Main conclusions  Environmental factors are important drivers for the β-diversity of spiders, especially across open habitats. This underlines the importance of preserving the whole range of moisture conditions in open habitats. Narrow niches of species occurring at the ends of both environmental gradients indicate that adaptations to extreme habitats lead to constraints in ecological flexibility. Nevertheless, the habitat niche of species seems to evolve much faster than morphological or physiological traits.