Tolerances Of Individual Species Research Articles

Exploration of Marine Lichenized Fungi as Bioindicators of Coastal Ocean Pollution in the Boston Harbor Islands National Recreation Area

This preliminary exploration of marine lichenized fungi (lichens) as bioindicators of water pollution examined the distribution of intertidal lichen communities in the Boston Harbor Islands National Recreation Area with respect to recorded pollution throughout the harbor. We found significant negative associations between pollution measurements and the health of the lichen community based on cover and species richness. We also observed significant differences in species composition between areas of higher pollution and areas of lower pollution, though not enough data are available to establish the pollution sensitivity or tolerance of individual species. We note that difficulties in the collection and identification of marine lichens hamper efforts to use them broadly as bioindicators. This study suggests that marine lichens could prove useful as bioindicators, but more research is needed to understand the differential effects of pollution on individual species as well as to establish practical procedures both for quantifying marine lichen community health and for widespread bioindication using marine lichens. Finally, one species collected during this study, Verrucaria ceuthocarpa, represents a first report for the Boston Harbor Islands National Recreation Area.

Multi-proxy evidence for Holocene lake-level and salinity changes at An Loch Mór, a coastal lake on the Aran Islands, Western Ireland

Curves for Holocene lake levels and salinity changes are presented for An Loch Mór, a small oligohaline lake on the Aran Islands off the west coast of Ireland, based on palaeoecological investigations of a 12 m long, lake-sediment core. New insights are also provided into Holocene sea-level change in the Galway Bay region. Particular emphasis has been placed on the ostracod fauna, both past and present. Salinity and lake-level changes were reconstructed from the fossil ostracod assemblages, based on the known tolerances of individual species and on the assemblages as a whole. Additional evidence was provided by other proxies including strontium–isotope ratios derived from ostracod shells and other carbonates, plant macrofossil and pollen analyses, and sedimentological changes. The early Holocene (pre-Boreal, i.e. 11.5–10 ka) was characterised by low lake levels and slightly elevated salinity values, probably the result of high evapotranspiration and low precipitation rather than elevated sea levels. Early Holocene plant and animal migration to the island does not seem to have been impeded but relative sea levels were not necessarily so low (below −40 m a.s.l.) that landbridges were present to the mainland. Between ca 10 and 8.5 ka, relatively high lake levels prevailed. At 8.3 and 7.5 ka, minor fluctuations (lowering) of the lake level occurred that are assumed to relate to early Holocene abrupt events. Beginning at 7.05 ka, lake levels declined sharply. A general trend towards rising lake levels started at ca 6.4 ka and accelerated at ca 5.6 ka as runoff increased as a result of Neolithic clearances. At ca 4.8 ka, lake levels began to rise once again, probably in response to changes in rainfall and/or evapotranspiration and runoff. Lower lake levels during the first half of the 1st millennium AD were probably a response to decreased runoff as a result of a drier climate coupled with regeneration of woody vegetation. The sharpest rise in both lake levels and salinity began during the ninth century AD, which is attributed to a rapid rise in relative sea level.

INSECTS OF THE BOREAL ZONE OF CANADA

AbstractThe boreal zone of Canada extends across the continent over millions of square kilometres. Characterizing the insects of this cool temperate zone is especially important for an understanding of the Canadian fauna in general, and for northern forestry. The boreal zone supports simple coniferous forests with some deciduous trees and an understory of a few common vascular plants, mosses, and lichens. This enormous area of apparently similar vegetation nevertheless shows very great spatial and temporal heterogeneity, with a wide range of subhabitats. Aquatic habitats of many different kinds are especially well represented in the zone. The diversity of terrestrial habitats is maintained chiefly by disturbance, especially fire and seasonal flooding, and contributes greatly to faunal diversity.About 22 000 insect species are estimated to occur in the zone, far fewer than in more southern zones. Northern taxa, notably Diptera, are relatively well represented. The distributions and patterns of variation of the species are summarized. About half have transcontinental ranges, and many occur also in forested habitats in the western mountains south of the boreal zone. About 8% of the species appear to be holarctic. Few species that occur in the boreal zone are strictly confined to it, however. Generalist species in fresh water and other widespread habitats are conspicuous. Many species are centred farther south, and extend northward into the zone to varying degrees.Adaptations to northern conditions have been reported in many boreal insects. For example, the short growing season is reflected by the prevalence of univoltine species. Insects survive the long cold winters by cold-hardiness and dormancies. Species from disturbed habitats disperse widely. The limited diversity of resources is confirmed by the fact that the food range of some groups of herbivores is wider than in their southern relatives.Boreal ecosystem relationships are complex, especially relative to the arctic. Numerous associations among insects, and between insects and other organisms, have been demonstrated. However, some evidence suggests that the structure of northern biotic communities might depend more on the tolerances of individual species than on interactions among the species.The population dynamics of boreal forest insects, notably the spruce budworm, are discussed. In view of the spatial and temporal complexity of the boreal zone, the diversity of interactions with abiotic and biotic factors, and the prevalence of data that correlate with rather than explain population changes, our current failure to understand “outbreaks” of certain boreal insects is not surprising, because many factors probably combine to determine the population of a given species at a given lime and place.Information on most aspects of the composition and biology of the boreal fauna is incomplete. Data on boreal species have been collected chiefly in southern transitional ecosystems adjacent to boreal zones, rather than in truly boreal systems. Basic taxonomic information on several important taxa, as well as detailed taxonomic and morphometric information about individual species, is especially scanty. However, substantial and coordinated studies of boreal faunas will yield information of great interest and value. Some approaches relevant to further work in taxonomic and ecological arenas are suggested.

Comparative Desiccation Tolerance of Three Desert Pteridophytes: Response to Long-term Desiccation

There are over 30 pteridophyte species in Big Bend National Park, Texas. While most are poikilohydrous, sharing some degree of physiological desiccation tolerance, individual species have distinctive distributions along an aridity gradient in the park. We examined three species with respect to the influence of extended desiccation on photosynthetic recovery over 24 h and desiccation-induced membrane damage. The low-elevation species Selaginella lepidophylla was least sensitive to extended desiccation and had the fastest photosynthetic recovery and the least membrane damage. The high-elevation species Cheilanthes tomentosa was most sensitive to extended desiccation and had the slowest photosynthetic recovery and the greatest membrane damage. The mid-elevation species Notholaena sinuata var. cochisensis was intermediate in response in all cases. These results document significant interspecific physiological differences that may influence the distributions of these desiccationtolerant pteridophytes along an aridity gradient in west Texas. INTRODUCTION Many nonvascular and vascular plants are capable of surviving almost total dehydration in their native habitats. These desiccation-tolerant species and their physiological and morphological adaptations have been the subjects of much research (Bewley, 1979). While desiccation tolerance is widely distributed, there may be a considerable degree of variation in apparent desiccation tolerance within broad taxonomic groups. Variation in desiccation tolerance has been frequently reported in lichens and bryophytes, and less often in intertidal algae (see Bewley and Krochko, 1982 for review and numerous references). Desiccation tolerance is an integrated physiological characteristic that may comprise many specific features and such variation may be expressed as differing sensitivities to frequency, duration, and rate of desiccation and differing rates and degrees of physiological recovery upon wetting. In virtually all cases, there is very good correlation between desiccation tolerance features and the water status of the habitats where particular species, or ecological races, are found. In contrast to these nonvascular groups, desiccation-tolerant pteridophytes have been infrequently studied from a comparative perspective. While desiccation tolerance of individual species has been studied (Oppenheimer and Halevy, 1962; Stuart, 1968; Nobel, 1978; Eickmeier, 1979), few physiologically based comparative studies are available (Eickmeier, 1980). Most often such studies are of a survey nature and only document drought-tolerance limits in a way that makes species comparisons difficult (Gaff, 1977; Gaff and Latz, 1978). This lack of detailed comparative studies is surprising since there are many pteridophytes native to arid desert regions of the southwestern U.S. that have distinct distributions along elevationally based aridity gradients. For example, Hevly (1963) examined the distributions and adaptations of cheilanthoid ferns along a 2400-m elevation gradient in Arizona. While species distributions did overlap to some degree, ferns in the genus Cheilanthes were found at the highest mean elevation, followed by species of the genus Pellaea, with members of the genus Notholaena being found at the lowest mean elevation. Hevly attempted to correlate morphological and anatomical features of the sporophytes and spore germination requirements with the observed distributions of the species. Aside from the fact that the species were apogamous, thereby eliminating the need of water for sexual reproduction, no clear ecological explanation was evident and Hevly (1963, p. 174) suggested that a comparative physiological study might be useful

Crustacean diversity in relation to the size of water bodies: some facts and problems

SUMMARY. Data on the crustacean faunas of 207 lowland water bodies in Yorkshire, involving 125 species, are discussed in relation to site area. Not unexpectedly, large water bodies generally have the most diverse faunas, but the relationship is not a simple one so far as individual species are concerned. While many show a progressive increase in percentage occurrence from small to large water bodies, the reverse is true for others. Chydorid cladocerans, of which twenty‐one species were recorded, show an unambiguous preference for large water bodies. While differences in habitat diversity appear insufficient to explain the almost seven‐fold difference in chydorid representation between ponds and large water bodies, there are also difficulties in attributing the situation to ease, or difficulty, of dispersal. The strategy of firmly attaching resting eggs to substrata employed by some chydorids is more likely to frustrate than to promote dispersal. General habits, ecological preferences and feeding habits of the commonest species are analysed in an attempt to clarify the relation of number of species to size of water body and some paradoxical features of dispersal are noted. Extrapolation from the data to very large lakes is shown to be misleading. Numerical data, even for a large number of water bodies, are no substitute for knowledge of the ecological requirements and tolerances of individual species. Examples are given of the rapid colonization of newly formed ponds by small crustaceans. The relevance of such observations to the theory of island biogeography and to various ecological problems, and the possibility of experimental work using small crustaceans and small ponds are noted.