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Michael Kleyer 《植被学杂志》1999,10(5):697-708
Abstract. In this study, plant functional types are understood as groups of plants with similar biological traits displaying significant optima or maxima on a gradient plane of resource supply and disturbance intensity. The biological traits refer to expansion, vegetative regeneration, generative reproduction, dispersal and seed bank longevity. 129 vegetation samples were taken in an agricultural landscape in southwestern Germany, covering a wide range of terrestrial vegetation types – but with the exception of forests and wetlands. For each site, also soil data were recorded. Mean daily soil moisture was estimated with a simple model. Soil moisture, balanced nitrogen supply and available phosphorus were combined into a factor ‘resource supply’. In addition, disturbance intensity was estimated for each site. This factor was based on (1) frequency of disturbance, (2) disturbance depth below or above the soil surface, and (3) proportion of the area affected by a discrete disturbance event. 30 plant groups with similar biological characteristics resulted from a cluster analysis, based on a compilation of 19 biological traits for a regional species pool. Logistic regression on a gradient plane of disturbance intensity and resource supply yielded response curves for 28 groups. The dependent variable was defined as the probability of encountering all members of a group in a sample. 17 groups display a significant response curve on the gradient plane. Plants with a potential for long- range dispersal are concentrated on sites with low or high disturbance intensities (e.g. fallow land, fields, lawns). On sites with medium disturbance intensity (e.g. meadows) and low to medium resource supply, small-range dispersal predominates. There are no distinct trends concerning seed bank longevity. The potential for vertical and lateral expansion increases with decreasing disturbance intensity. Only at medium disturbance intensities does vertical expansion correlate positively with resource supply. Rapid detachment of daughter individuals occurs more often on productive sites than on less productive sites. Diversity of groups with similar biological traits is highest on sites with medium disturbance intensities. 相似文献
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Does hydraulic lift exist in shallow-rooted species? A quantitative examination with a half-shrub Gutierrezia sarothrae 总被引:1,自引:0,他引:1
Hydraulic lift occurs in some deep-rooted shrub and herbaceous species. In this process, water taken up by deep roots from
the moist subsoil is delivered to the drier topsoil where it is later reabsorbed by shallow roots. However, little is known
about the existence of hydraulic lift in shallow-rooted xeric species. The objectives of this study were 1) to ascertain whether
hydraulic lift exists in Gutierrezia sarothrae (broom snakeweed), a widespread North American desert species with a shallow root system, grown in pot and field conditions
and 2) if it does, how much water can be transferred from the subsoil to the 30 cm topsoil during the night. Snakeweed seedlings
were transplanted in buried pots allowing the deeper roots to grow into the subsoil 30 cm below the surface. Soil water content
inside and outside of the pot was measured seasonally and diurnally with time domain reflectometry technique (TDR). An increase
in water content was detected in the pot after the plant was covered for 3 h by an opaque plastic bag during the day, suggesting
hydraulic lift from deeper depths and exudation of water into the drier topsoil. Root exudation was also observed on native
range sites dominated by snakeweed. Water efflux in the pot was 271 g per plant per night. which was equivalent to 15.3% of
the extrapolated, porometer-derived whole-plant daily transpiration. Hydraulic lift observed in Gutierrezia improved water uptake during the day when evaporative demand is high and less water is available in the topsoil. We concluded
that hydraulic lift might help snakeweed to alleviate the effect of water stress. 相似文献
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Pernilla Christensen Frauke Ecke Per Sandström Mats Nilsson Birger Hörnfeldt 《Population Ecology》2008,50(2):169-179
There has been a long-term decline in spring and fall numbers of Clethrionomys rufocanus in boreal Sweden in 1971–2005. Previous studies on permanent sampling plots in the centre of 2.5 × 2.5 km landscapes suggested
that habitat fragmentation (sensu destruction) could have contributed to the decline. Therefore, we tested these findings
in a field study and compared trapping results on the central sampling plots of landscapes with a low degree of fragmentation
(LDF) and of “hot spot” type with trapping results in managed forest landscapes with a high degree of fragmentation (HDF).
We predicted that C. rufocanus would be more common on the LDF plots. We used our permanent plots supplemented with a new sample of plots, mainly of the
rare LDF type, inside or just outside the long-term study area. Very few voles were trapped on both plot types, and no difference
was found. However, a subsequent pilot study with trapping in a national park with large areas of pristine, unfragmented forest
yielded more voles than in the managed, more fragmented, areas. Consequently, the initial field study data and some other
recent data were also re-analysed from a “local patch quality” perspective. This alternative approach revealed the positive
importance of large focal patches of forest >60 years old and their content of old-growth (pine) forest (>100 years). Interestingly,
at the landscape level, the frequency distribution of patches of forest >60 years old, old-growth (>100 years), and especially
of old-growth pine forest (>100 years), relative to the properties of plots with C. rufocanus, suggested that there are few forest patches left that are suitable for C. rufocanus. Our current results suggest that habitat fragmentation cannot be excluded as a contributing cause to the long-term decline
of C. rufocanus in boreal Sweden. 相似文献
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Nine pairs of polymerase chain reaction (PCR) primers that amplify polymorphic microsatellite loci in the desert locust, Schistocerca gregaria (Forskal), were developed using a magnetic bead‐based enrichment protocol. A sample of 48 locusts collected during the 1993 and 1995 upsurge periods in Eritrea, East Africa, were genotyped. The number of alleles per locus ranged from six to 20; the average was 12.67. Allelic distributions were significantly different between samples from different localities. 相似文献
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Mélody Porlier Marc Bélisle Dany Garant 《Philosophical transactions of the Royal Society of London. Series B, Biological sciences》2009,364(1523):1543-1554
Improving our knowledge of the links between ecology and evolution is especially critical in the actual context of global rapid environmental changes. A critical step in that direction is to quantify how variation in ecological factors linked to habitat modifications might shape observed levels of genetic variability in wild populations. Still, little is known on the factors affecting levels and distribution of genetic diversity at the individual level, despite its vital underlying role in evolutionary processes. In this study, we assessed the effects of habitat quality on population structure and individual genetic diversity of tree swallows (Tachycineta bicolor) breeding along a gradient of agricultural intensification in southern Québec, Canada. Using a landscape genetics approach, we found that individual genetic diversity was greater in poorer quality habitats. This counter-intuitive result was partly explained by the settlement patterns of tree swallows across the landscape. Individuals of higher genetic diversity arrived earlier on their breeding grounds and settled in the first available habitats, which correspond to intensive cultures. Our results highlight the importance of investigating the effects of environmental variability on individual genetic diversity, and of integrating information on landscape structure when conducting such studies. 相似文献