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Spatiotemporal Variation (spatiotemporal + variation)
Selected AbstractsEcological feedbacks and the evolution of resistanceJOURNAL OF ANIMAL ECOLOGY, Issue 6 2009Meghan A. Duffy Summary 1. ,The idea that parasites can affect host diversity is pervasive, and the possibility that parasites can increase host diversity is of particular interest. In this review, we focus on diversity in the resistance of hosts to their parasites, and on the different ways in which parasites can increase or decrease this resistance diversity. 2. ,Theoretically, parasites can exert many different types of selection on host populations, which each have consequences for host diversity. Specifically, theory predicts that parasites can exert negative frequency-dependent selection (NFDS) and disruptive selection on resistance, both of which increase host diversity, as well as directional selection and stabilizing selection on resistance, both of which decrease host diversity. 3. ,Despite these theoretical predictions, most biologists think of only NFDS or directional selection for increased resistance in response to parasitism. Here, we present empirical support for all of these types of selection occurring in natural populations. Interestingly, several recent studies demonstrate that there is spatiotemporal variation in the type of selection that occurs (and, therefore, in the effects of parasitism on host diversity). 4. ,A key question that remains, then, is: What determines the type of parasite-mediated selection that occurs? Theory demonstrates that the answer to this question lies, at least in part, with trade-offs associated with resistance. Specifically, the type of evolution that occurs depends critically on the strength and shape of these trade-offs. This, combined with empirical evidence for a strong effect of environment on the shape and strength of trade-offs, may explain the observed spatiotemporal variation in parasite-mediated selection. 5. ,We conclude that spatiotemporal variation in parasite-driven evolution is likely to be common, and that this variation may be driven by ecological factors. We suggest that the feedback between ecological and evolutionary dynamics in host,parasite interactions is likely to be a productive area of research. In particular, studies addressing the role of ecological factors (e.g. productivity and predation regimes) in driving the outcome of parasite-mediated selection on host populations are warranted. Such studies are necessary if we are to understand the mechanisms underlying the observed variation in the effects of parasites on host diversity. [source] Microsatellite diversity and genetic structure of fragmented populations of the rare, fire-dependent shrub Grevillea macleayanaMOLECULAR ECOLOGY, Issue 6 2002Phillip R. England Abstract Recent habitat loss and fragmentation superimposed upon ancient patterns of population subdivision are likely to have produced low levels of neutral genetic diversity and marked genetic structure in many plant species. The genetic effects of habitat fragmentation may be most pronounced in species that form small populations, are fully self-compatible and have limited seed dispersal. However, long-lived seed banks, mobile pollinators and long adult lifespans may prevent or delay the accumulation of genetic effects. We studied a rare Australian shrub species, Grevillea macleayana (Proteaceae), that occurs in many small populations, is self-compatible and has restricted seed dispersal. However, it has a relatively long adult lifespan (c. 30 years), a long-lived seed bank that germinates after fire and is pollinated by birds that are numerous and highly mobile. These latter characteristics raise the possibility that populations in the past may have been effectively large and genetically homogeneous. Using six microsatellites, we found that G. macleayana may have relatively low within-population diversity (3.2,4.2 alleles/locus; Hexp= 0.420,0.530), significant population differentiation and moderate genetic structure (FST = 0.218) showing isolation by distance, consistent with historically low gene flow. The frequency distribution of allele sizes suggest that this geographical differentiation is being driven by mutation. We found a lack mutation-drift equilibrium in some populations that is indicative of population bottlenecks. Combined with evidence for large spatiotemporal variation of selfing rates, this suggests that fluctuating population sizes characterize the demography in this species, promoting genetic drift. We argue that natural patterns of pollen and seed dispersal, coupled with the patchy, fire-shaped distribution, may have restricted long-distance gene flow in the past. [source] Trichome production and spatiotemporal variation in herbivory in the perennial herb Arabidopsis lyrataOIKOS, Issue 1 2007Geir Løe Allocation theory suggests that the optimal level of resistance against herbivores should vary with the risk of herbivory if allocation to resistance is costly. The perennial herb Arabidopsis lyrata has a genetically based polymorphism for trichome production and occurs in a glabrous and a trichome-producing form. Leaf trichomes (hairs) can protect plants against insect herbivores, and may increase tolerance to drought and UV-radiation. To examine the functional significance of trichome production, we documented the frequency of glabrous plants and damage by insect herbivores in 30 A. lyrata populations in Sweden and Norway. The proportion of glabrous plants ranged from 0.10 to 0.71 (median=0.44) in polymorphic populations; 7 of 12 populations in Norway and 14 of 18 populations in Sweden were monomorphic glabrous, i.e. with fewer than 5% trichome-producing plants. The mean proportion of the leaf area removed by herbivores varied substantially among populations and years. With few exceptions, glabrous plants were more damaged than trichome-producing plants in polymorphic populations. The intensity of herbivory quantified as the mean damage to glabrous plants tended to be higher in polymorphic populations than in populations monomorphic for the glabrous morph and was higher in Sweden than in Norway. In Norway, both the magnitude of herbivore damage and the frequency of trichome-producing plants tended to decrease with increasing altitude. The results indicate that leaf trichomes contribute to resistance against herbivorous insects in A. lyrata, and suggest that herbivore-mediated selection contributes to the maintenance of the polymorphism in trichome production. [source] ROCK-SURFACE TEMPERATURES OF BASALT IN THE DRAKENSBERG ALPINE ENVIRONMENT, LESOTHOGEOGRAFISKA ANNALER SERIES A: PHYSICAL GEOGRAPHY, Issue 3 2007STEFAN GRAB ABSTRACT. Rock temperature data are presented for a variety of topographic localities at a high Drakensberg site. The objective is to investigate the spatiotemporal variations of surface rock temperatures in high Drakensberg basalt. The temperature results are then used to discuss possible implications for thermal stress fatigue and frost-induced weathering. TinytalkÔ data loggers and probes were used for rock-surface temperature recording. Long-term measurements were recorded over 12 months from May 2002 to April 2003, at a 1-hour logging interval and rock depth of 1 cm for a highaltitude (3300 m a.s.l.) interfluve and fracture site. Whilst the north-facing rock surface experiences negligible hours below ,3°C, the south-facing rock surface and interfluve sites are subjected to considerable periods below ,3°C, which falls within the ,frost cracking window'. It is concluded that the substantial contrasts of recorded rock thermal parameters over small spatial scales between various topographic settings, highlight that site-specific measurements across the broader scale are required for an adequate evaluation of regional weathering and its associated landform development. [source] Seasonal differences in the adaptability of herbage species to environmental variations in a long-term grazing experimentGRASSLAND SCIENCE, Issue 1 2007Yiruhan Abstract Mixtures of orchardgrass, perennial ryegrass, tall fescue, redtop, Kentucky bluegrass, and white clover were sown in autumn 1973. Two 8-year grazing experiments were conducted at the National Grassland Research Institute (Nasushiobara, Japan) to determine the effects of grazing intensity and nitrogen levels on pasture ecosystems. These experiments involved two different grazing intensities (1974,1981) and two different nitrogen levels (1982,1989). Large spatiotemporal variations in phytomass due to environmental variations were observed in both experiments. Finlay,Wilkinson analysis was applied to clarify seasonal (monthly) differences in the adaptability of the herbage species, as measured by phytomass, to environmental variations by year and treatments in the two experiments. Seasonality in the adaptability to environments differed greatly among species. In this paper, we examined from livestock farmers' standpoint whether seasonality in adaptability of herbage species in the grazing pasture could be satisfied. A significantly high adaptability was shown for: orchardgrass from May to July and November; tall fescue in April, June and July, and November; redtop and Kentucky bluegrass in April; and Zoysia japonica in September and October. In contrast, perennial ryegrass and white clover exhibited very low adaptability in any season. Z. japonica and weeds such as Pennisetum alopecuroides, Eragrostis ferruginea and Digitaria adscendens, which had invaded from surrounding areas, showed low adaptability, except in autumn, when they showed moderate adaptability. [source] | ||||||||||