The Interplay Between Life History and Environmental Stochasticity: Implications for the Management of Exploited Lizard Populations

SYNOPSIS. The sustainable use of wild species by local peopleis emerging as an important conservation strategy. The premiseis the economic value of species will justify their own preservationas well as the habitats they occupy. However, the lack of naturalhistory and demographic information for the majority of speciesbeing exploited or with potential uses presents challengingproblems for implementing sustainable use programs. Each yearin Argentina and Paraguay, an average of 1.9 million tegu lizardsof the genus Tupinambis are exploited for their skins. In spiteof the importance of tegus as a resource, their biology is poorlyknown and their populations have never been managed. The lifehistory of Tupinambis, like that of other exploited lizards,is characterized by a relatively long life span, a large clutchsize, several years of growth before reproduction, and highmortality of hatchlings. Importantly, the mortality of young-of-the-yearand the proportion of females reproducing each year are bothprobably strongly influenced by interannual environmental variation.Whenthese parameters were randomized in life table projections tosimulate the effects of environmental stochasticity, the populationgrowth rate was highly sensitive to environmental fluctuations.Monte Carlo simulations of different harvest strategies showedthat estimates of population growth rates were overwhelminglyinfluenced by environmental variation and the number of yearsincluded in the growth rate estimate, even in the face of seeminglylarge changes in adult mortality that would result from populationmanagement. These results are both encouraging and cautionaryfor Tupinambis conservation. On the one hand these patternscan help explain how Tupinambis populations may have persistedin spite of high and variable harvest levels during many years,but conversely, stochastic effects make it difficult to evaluatethe effects of conservation measures. Size and sex can be determinedfrom harvested skins, and pilot studies suggest that analysesof the annual harvest can provide valuable information for evaluatinglong-term population trends.     

Consequences of differences in body mass,wing length and leg morphology for nectar-feeding birds

Nectar-feeding birds are prominent in many parts of the world, and vary with respect to body size. Despite the availability of considerable morphometric data, few concerted efforts have been made to assess the influence of attributes such as mass, wing length and leg morphology upon the speed, acceleration, mode and energetic cost of movement by birds between flowers when foraging for nectar. This review attempts to consolidate and interpret available data and highlight areas where further investigations appear warranted. Australian honeyeaters are generally larger, and American hummingbirds smaller, than Hawaiian honeycreepers and sunbirds of Africa or Asia. Sunbirds, honeyeaters and honeycreepers generally perch while extracting nectar from flowers. Hummingbirds usually hover, apparently because suitable perches close to flowers are lacking, and not because hovering increases the speed at which flowers can be visited. Honeyeaters move from one flower to another at speeds that are at least as great as those for hummingbirds. Most passerine nectarivores need to ingest more nectar per day than hummingbirds in order to maintain energy balance, some species devoting more than 60% of the day to foraging. The major consequence of reduced foraging activity by hummingbirds, which spend only 5–30% of the day in this manner, appears to be male emancipation from nest construction and care of offspring. Large nectarivores have a greater capacity to store surplus food and to fast than smaller birds, and so can take advantage of short-lived peaks in nectar abundance. Nectarivores such as honeyeaters should therefore be favoured by the rapid diurnal changes in nectar availability which are characteristic of many Australian and African habitats. Body mass also determines the likely access to rich sources of nectar through size-related interspecific dominance hierarchies. In all families, larger species tend to monopolize the most rewarding nectar supplies, forcing smaller subordinate species to use poorer, more scattered sources. Within particular species, males usually have longer wings and greater masses than females. These variations imply that the two sexes differ with regard to their foraging ecology, although few supporting data are currently available.     

Impacts of climate warming and habitat loss on extinctions at species' low-latitude range boundaries

Polewards expansions of species' distributions have been attributed to climate warming, but evidence for climate‐driven local extinctions at warm (low latitude/elevation) boundaries is equivocal. We surveyed the four species of butterflies that reach their southern limits in Britain. We visited 421 sites where the species had been recorded previously to determine whether recent extinctions were primarily due to climate or habitat changes. Coenonympha tullia had become extinct at 52% of study sites and all losses were associated with habitat degradation. Aricia artaxerxes was extinct from 50% of sites, with approximately one‐third to half of extinctions associated with climate‐related factors and the remainder with habitat loss. For Erebia aethiops (extinct from 24% of sites), approximately a quarter of the extinctions were associated with habitat and three‐quarters with climate. For Erebia epiphron, extinctions (37% of sites) were attributed mainly to climate with almost no habitat effects. For the three species affected by climate, range boundaries retracted 70–100 km northwards (A. artaxerxes, E. aethiops) and 130–150 m uphill (E. epiphron) in the sample of sites analysed. These shifts are consistent with estimated latitudinal and elevational temperature shifts of 88 km northwards and 98 m uphill over the 19‐year study period. These results suggest that the southern/warm range margins of some species are as sensitive to climate change as are northern/cool margins. Our data indicate that climate warming has been of comparable importance to habitat loss in driving local extinctions of northern species over the past few decades; future climate warming is likely to jeopardize the long‐term survival of many northern and mountain species.     

Rampant drift in artificially fragmented populations of the endangered tidewater goby (Eucyclogobius newberryi)

Habitat fragmentation and its genetic consequences are a critically important issue in evaluating the evolutionary penalties of human habitat modification. Here, we examine the genetic structure and diversity in naturally subdivided and artificially fragmented populations of the endangered tidewater goby (Eucyclogobius newberryi), a small fish restricted to discrete coastal lagoons and estuaries in California, USA. We use five naturally fragmented coastal populations from a 300‐ km spatial scale as a standard to assess migration and drift relative to eight artificially fragmented bay populations from a 30‐ km spatial scale. Using nine microsatellite loci in 621 individuals, and a 522‐base fragment of mitochondrial DNA control region from 103 individuals, we found striking differences in the relative influences of migration and drift on genetic variation at these two scales. Overall, the artificially fragmented populations exhibited a consistent pattern of higher genetic differentiation and significantly lower genetic diversity relative to the naturally fragmented populations. Thus, even in a species characterized by habitat isolation and subdivision, further artificial fragmentation appears to result in substantial population genetic consequences and may not be sustainable.     

中国蝶类新种小志Ⅳ

本文记述国产眼蝶科(Satyridae)的一个新属Sinonympha与它的一个模式种Sinonympha amoena(新种),这一蝶类最早是笔者于1939年7月在我国四川省西北部的杂谷脑(理县)发见的。为欲较全面地了解它们在分类系统上的亲缘关系,又于1963年和1964年在原产地采集了大量的成虫标本,并于1965—1966年在北京饲养了它的幼期。 新华新眼蝶属Sinonympha新属 新属属征 新华新眼蝶属Sinonympha(新属)与Coenonympha Hbner(1819)较为近似,但是某些形态特征和生物学特性(包括幼期)则与Ypthima Hbner(1818),OeneisHbner(1819)以及Mycalesis Hbner(1818)等属的种类互有相似之处,现将本新属的主要特征列述于下:     

Theileria gilberti n. sp. (Apicomplexa: Theileriidae) in the Gilbert's Potoroo (Potorous gilbertii)

ABSTRACT. The morphology and genetic characterisation of a new species of piroplasm identified in the blood of the Gilbert's potoroo ( Potorous gilbertii ) from the Two Peoples Bay Nature Reserve near Albany, Western Australia, is described from blood and tissue samples from 16 Gilbert's potoroos. Microscopy of blood showed these parasites are highly pleomorphic with a mean length of 1.8 μm and mean width of 0.85 μm. Phylogenetic analysis of 18S rRNA sequence data identified the piroplasm as a new species of Theileria that is closely related to other Australian marsupial piroplasm species. Based on biological and molecular data, it is proposed that the parasite from Gilbert's potoroo be given the name Theileria gilberti n. sp.     

Sensitive detection of mycoplasmalike organisms in field-collected and in vitro propagated plants of Brassica, Hydrangea and Chrysanthemum by polymerase chain reaction

A polymerase chain reaction (PCR) protocol, previously designed for amplification of a DNA fragment from aster yellows mycoplasmalike organism (MLO), was employed to investigate the detection of MLO DNA in field-collected and in vitro micropropagated plants. PCR with template DNA extracted from symptomatic, naturally-infected samples of Brassica, Chrysanthemum and Hydrangea, each yielded a DNA band corresponding to 1.0 Kbp. However, no DNA product was observed when either infected Ranunculus (with phyllody disease) or Gladiolus with (symptoms of ‘germs fins’) was used as source of template nucleic acid for PCR; further experiments indicated absence of target DNA in the case of Ranunculus and the presence of substances in Gladiolus which inhibited the PCR. The MLO-specific DNA was detected by PCR using less than 95 pg of total nucleic acid (equivalent to total nucleic acid from 1.9, ug tissue) in the case of field-collected Hydrangea and less than 11.4 pg of nucleic acid (equivalent to total nucleic acid from 19 ng of tissue) in the case of field-collected Brassica. The findings illustrate highly sensitive detection of MLOs in both field-grown and in vitro micropropagated infected plants.     

Carbon isotopes as indicators of elephant diets and African environments

Stable carbon isotope ratios have been successfully used to assess modern animal diets and to reconstruct prehistoric diets of animals and humans (Vogel & van der Merwe, 1977; van der Merwe & Vogel, 1978; Burleigh & Brothwell, 1978; Vogel, 1978a; DeNiro & Epstein, 1978; Tieszen et al., 1979; Tieszen & Imbamba, 1980; Chisholm, Nelson & Schwarcz, 1982; Tauber, 1981). We have used ¹³C/¹²C ratio measurements of bone collagen to study the diets of African elephants in twelve wildlife refuges. These represent most of the habitats in which elephants live, including such diverse plant communities as primary rain forest, savanna woodland and desert. The δ¹³C values were found to have a simple linear relationship with tree density in most cases. When translated into relative amounts of dietary browse (C₃ plants) and graze (C₄ plants), the grass content is seen to be systematically under-represented, presumably due to inefficient metabolism. This does not affect the relationship between elephant diet and tree density, which has implications for the study of elephant-woodland interactions, and for reconstructions of past African environments.     

Climate controls on C3 vs. C4 productivity in North American grasslands from carbon isotope composition of soil organic matter

We analyzed the δ¹³C of soil organic matter (SOM) and fine roots from 55 native grassland sites widely distributed across the US and Canadian Great Plains to examine the relative production of C₃ vs. C₄ plants (hereafter %C₄) at the continental scale. Our climate vs. %C₄ results agreed well with North American field studies on %C₄, but showed bias with respect to %C₄ from a US vegetation database (statsgo ) and weak agreement with a physiologically based prediction that depends on crossover temperature. Although monthly average temperatures have been used in many studies to predict %C₄, our analysis shows that high temperatures are better predictors of %C₄. In particular, we found that July climate (average of daily high temperature and month's total rainfall) predicted %C₄ better than other months, seasons or annual averages, suggesting that the outcome of competition between C₃ and C₄ plants in North American grasslands was particularly sensitive to climate during this narrow window of time. Root δ¹³C increased about 1‰ between the A and B horizon, suggesting that C₄ roots become relatively more common than C₃ roots with depth. These differences in depth distribution likely contribute to the isotopic enrichment with depth in SOM where both C₃ and C₄ grasses are present.