Showing papers in "Acta Oecologica-international Journal of Ecology in 2004"

Small mammal abundance in Mediterranean post-fire habitats: a role for predators?

Abstract: We studied patterns of small mammal abundance and species richness in post-fire habitats by sampling 33 plots (225 m 2 each) representing different stages of vegetation recovery after fire. Small mammal abundance was estimated by live trapping during early spring 1999 and vegetation structure was sampled by visual estimation at the same plots. Recently–burnt areas were characterised by shrubby and herbaceous vegetation with low structural variability, and unburnt areas were characterised by well developed forest cover with high structural complexity. Small mammal abundance and species richness decreased with time elapsed since the last fire (from 5 to at least 50 years), and these differences were associated to the decreasing cover of short shrubs as the post-fire succession of plant communities advanced. However, relationships between vegetation structure and small mammals differed among areas burned in different times, with weak or negative relationship in recently burnt areas and positive and stronger relationship in unburnt areas. Furthermore, the abundance of small mammals was larger than expected from vegetation structure in plots burned recently whereas the contrary pattern was found in unburned areas. We hypothesised that the pattern observed could be related to the responses of small mammal predators to changes in vegetation and landscape structure promoted by fire. Fire-related fragmentation could have promoted the isolation of forest predators (owls and carnivores) in unburned forest patches, a fact that could have produced a higher predation pressure for small mammals. Conversely, small mammal populations would have been enhanced in early post-fire stages by lower predator numbers combined with better predator protection in areas covered by resprouting woody vegetation.

Testing the spectral variation hypothesis by using satellite multispectral images

Abstract: In the present paper, a test of the spectral variation hypothesis (SVH) was performed using multispectral high resolution satellite data. The SVH was tested by comparing the relationship between the spectral heterogeneity and species richness in plots of different size (100– 10000 m 2 ) in a complex wetland ecosystem, the “Montepulciano Lake”, Central Italy. The nature reserve of the Montepulciano Lake is centered on a 100 ha shallow lake surrounded on three sides by aPhragmitesaustralis andCarex sp. pl. marsh of about 280 ha. The monitoring program for the reserve vegetation started in 2002 and is based on the analysis of 1, 100 m 2 and 1 ha (10000 m 2 ) plots, organized in such a manner that four of the smaller size plots are nested, following a random design, within a larger one. Data on species composition and community structure were collected in the plots and stored in a GIS-linked archive. A multispectral Quickbird satellite image (3 m spatial resolution) acquired of the wetland and lake ecosystem during the same period was radiometrically and geometrically corrected. We performed an analysis to examine the use of spectral heterogeneity using the four visible and infrared wavebands of the satellite image to predict species richness at the different spatial scales. The spectral heterogeneity was found to explain about 20% of the variance of species richness at the 100 m 2 scale and about 50% at the 1 ha scale. It was concluded that multispectral high resolution satellite data can contribute to the biodiversity assessment of complex wetland ecosystems.

Plants as seed traps: inter-specific interference with dispersal

Abstract: Established plants may disrupt patterns of seed deposition by physically trapping dispersing seed. In this study we quantified seed trapping at very fine spatial scales, by measuring seed fall of two ericaceous dwarf shrub species at a range of distances from allospecific shrubs within a matrix of short grass vegetation. Next to allospecific bushes, seed deposition densities of Calluna vulgaris and Erica cinerea were between 7- and 20-fold higher than those in the short grass. This increase is comparable to deposition densities next to conspecific bushes, caused by local dispersal, which were 19–33-fold greater than the background seed rain. Seed densities decayed rapidly with distance from the allospecific bush, so that in general the bush’s influence on deposition extended <0.1 m. By causing localised, extreme peaks in seed density around established plants, seed trapping could have large effects on the fitness of plants dispersing seed and on the spatial pattern of recruitment across plant communities.

Factors affecting plant species composition of hedgerows: relative importance and hierarchy

Abstract: Although there has been a clear quantitative and qualitative decline in traditional hedgerow network landscapes during last century, hedgerows are crucial for the conservation of rural biodiversity, functioning as an important habitat, refuge and corridor for numerous species. To safeguard this conservation function, insight in the basic organizing principles of hedgerow plant communities is needed. The vegetation composition of 511 individual hedgerows situated within an ancient hedgerow network landscape in Flanders, Belgium was recorded, in combination with a wide range of explanatory variables, including a selection of spatial variables. Non-parametric statistics in combination with multivariate data analysis techniques were used to study the effect of individual explanatory variables. Next, variables were grouped in five distinct subsets and the relative importance of these variable groups was assessed by two related variation partitioning techniques, partial regression and partial canonical correspondence analysis, taking into account explicitly the existence of intercorrelations between variables of different factor groups. Most explanatory variables affected significantly hedgerow species richness and composition. Multivariate analysis showed that, besides adjacent land use, hedgerow management, soil conditions, hedgerow type and origin, the role of other factors such as hedge dimensions, intactness, etc., could certainly not be neglected. Furthermore, both methods revealed the same overall ranking of the five distinct factor groups. Besides a predominant impact of abiotic environmental conditions, it was found that management variables and structural aspects have a relatively larger influence on the distribution of plant species in hedgerows than their historical background or spatial configuration.

Do rhizome severing and shoot defoliation affect clonal growth of Leymus chinensis at ramet population level

Abstract: Leymus chinensis (Trin.) Tzvel. is a perennial species of Gramineae, usually subject to defoliation from grazing and mowing. We examined whether shoot defoliation and rhizome severing affected rhizome and ramet growth, and vegetative bud outgrowth of L. chinensis ramet populations. We also tested the hypothesis that clonal growth of the ramets subject to defoliation would benefit from clonal integration between interconnected ramets besides from possible compensatory growth. To 48 experimental plots, we applied six treatments resulting from interactions between two rhizome connection states (unsevered/severed) and three defoliation regimes (non-defoliated, mildly-defoliated and heavily-defoliated). Defoliation affected rhizome growth and bud outgrowth, but had little effect on shoot growth. Mild and heavy defoliation exerted similar effects on rhizome growth. Only heavy defoliation significantly reduced bud outgrowth while mild defoliation did not. The fact that shoot growth did not change after defoliation and that the bud numbers remained unchanged after mild defoliation suggest that the compensatory response enable the species to tolerate grazing to some extent. Neither rhizome severing nor the interaction of rhizome severing and defoliation had effect on any tested variables. Lack of the effect of rhizome severing falsified the first half of our hypothesis, that is, clonal integration was unimportant in our experiment. The probable reasons were suspected to be the short duration of the experiment and/or the buffer effect of carbohydrate reserves in rhizomes for shoot growth and bud production in time of defoliation.

Anatomical basis of the change in leaf mass per area and nitrogen investment with relative irradiance within the canopy of eight temperate tree species

Abstract: Changes in leaf mass per area (LMA), nitrogen content on a mass-basis (Nm) and on an area basis (Na) with relative irradiance were assessed in leaves of eight temperate species harvested at different depths in a canopy. Relative irradiance (GSF) at the points of leaf sampling was estimated by hemispheric photographs. There was a strong species-dependent positive relationship between LMA and GSF for all species. Shade-tolerant species such as Fagus sylvatica showed lower LMA for the same GSF than less tolerant species as Quercus pyrenaica or Quercus petraea. The only evergreen species in the study, Ilex aquifollium, had the highest LMA, independent of light environment, with minimum values much higher than the rest of the broad-leaved species studied. There was no relation between Nm and GSF for most species studied and only a very weak relation for the relative shade-intolerant species Q. pyrenaica. Within each species, the pattern of Na investment with regard to GSF was linked mainly to LMA. At the same relative irradiance, differences in Na among species were conditioned both by the LMA–GSF relationship and by the species Nm value. The lowest Nm value was measured in I. aquifollium (14.3 ± 0.6 mg g–1); intermediate values in Crataegus monogyna (16.9 ± 0.6 mg g–1) and Prunus avium (19.1 ± 0.6 mg g–1) and higher values, all in a narrow range (21.3 ± 0.6 to 23 ± 0.6 mg g–1), were measured for the other five species. Changes in LMA with the relative irradiance were linked both to lamina thickness (LT) and to palisade/spongy parenchyma ratio (PP/SP). In the second case, the LMA changes may be related to an increase in lamina density as palisade parenchyma involves higher cell packing than spongy parenchyma. However, since PP/SP ratio showed a weak species-specific relationship with LMA, the increase in LT should be the main cause of LMA variation.

Afforestation with Pinus halepensis reduces native shrub performance in a Mediterranean semiarid area

Abstract: It has been often suggested that the introduction of Pinus halepensis with afforestation could facilitate long-term colonisation and development of late-successional species in Mediterranean dry and semiarid areas, but this affirmation has rarely been experimentally tested in the field In this study, we analyse the effects of planted P halepensis density (0, 1500 and 3470 trees·ha –1 ) on soil moisture at two depths (0–10 and 10–30 cm), and on the physiological status of three shrub species (Quercus coccifera, Erica multiflora and Rhamnus lycioides )i n a semiarid area of SE Spain Afforestation with P halepensis had a negative effect on soil moisture, an effect that increased with tree density This effect was more pronounced at 0–10 cm depth than at 10–30 cm depth, and was especially evident after the spring and late summer rainfalls During spring and summer, mean predawn water potentials in the area without P halepensis were –15, –24 and –22 MPa for Q coccifera, E multiflora, and R lycioides, respectively Mean net photosynthesis values in the same area and period were 12, 10 and 15 µmol CO2 m –2 s –1 for Q coccifera, E multiflora, and R lycioides, respectively Similarly, mean stomatal conductance was 151, 164 and 217 mmol H2 Om –2 s –1 for Q coccifera, E multiflora, and R lycioides, respectively Values were substantially reduced (up to 56%) with increasing P halepensis density, suggesting the presence of a strong competition for water Our results provide evidence that the introduction of P halepensis with afforestation has a negative effect on existing late-successional shrubs, and suggest that this introduction does not stimulate successional processes in Mediterranean semiarid areas

Morphological plasticity in response to shading in three Convolvulus species of different ecological breadth

Abstract: We evaluated in common-garden experiments the morphological plasticity to shading of three Convolvulus species that occur in Chile and differ in ecological breadth. Convolvulus arvensis L. is a world weed distributed along the country, and is found in open as well as in shaded habitats. Convolvulus chilensis Pers. is a Chilean endemic species typical of coastal habitats, and is found in open to partially open sites. C.demissus choisy occurs only on slopes of the Andes of Chile and Argentina, habitats with high incidence of solar radiation. We hypothesized that the magnitude of phenotypic plasticity to shading of these species would correlate with their ecological breadth. Shading had a significant effect on internode length, petiole length, stem diameter, stem length, number of branches, leaf area, leaf shape, leaf biomass, and specific leaf area. Species differed in all the morphological traits except leaf biomass. A significant Shading × Species interaction in the two-way ANOVA, i.e. differential plasticity to shading of Convolvulus species, was found for petiole length, stem length, number of branches, leaf shape, and specific leaf area. Contrary to our hypothesis, tests of parallelism showed that, in general, the plasticity to shading of C. chilensis (the species of intermediate ecological breadth) was the greatest, and that of C. arvensis (the weed) and C. demissus (the species of narrow distribution) was similar. Issues of ecotype differentiation, in the case ofC. arvensis, and the role of life history traits are raised to explain the observed lack of association between ecological breadth and magnitude of phenotypic plasticity. © 2004 Elsevier SAS. All rights reserved.

Effects of soil moisture regimes on photosynthesis and growth in cattail (Typha latifolia)

Abstract: Both waterlogging and water deficiency are major environmental factors affecting plant growth and functioning in many wetland and floodplain ecosystems across North America. Wetland plants possess various characteristics that enable them to survive and function in the intermittently flooded wetland environments, while their sensitivity to drought has received less attention. The present study quantified the photosynthetic and growth responses of cattail (Typha latifolia), an important species of freshwater wetlands, to a wide range of soil moisture regimes. In addition, changes in the efficiency of photosynthetic apparatus following initiation of the treatments were investigated. Under greenhouse conditions, seedlings were subjected to four soil moisture regimes: (1) drained (control), (2) continuous flooding, (3) periodic flooding, and (4) periodic drought. Results indicated that dark fluorescence yield was increased in response to periodic drought, while it showed decreases under continuous flooding. Net photosynthesis and stomatal conductance were enhanced by continuous flooding and periodic flooding. In contrast, these parameters exhibited reduction under periodic drought. In addition, leaf chlorophyll content was adversely affected by periodic drought. Recovery of net photosynthesis was noted, along with enhanced height growth, in both continuously and periodically flooded plants. Meanwhile, continuous flooding enhanced biomass production while periodic drought led to biomass reduction. Periodic drought also contributed to substantial reduction in root growth compared with shoot growth. Therefore, the combined photosynthetic performance and growth responses of cattail are likely to contribute to the ability of this species to thrive in flooded condition but be susceptive to periodic drought.

Effects of seed mass on seedling success in Artocarpus heterophyllus L., a tropical tree species of north-east India

Abstract: I examined the effects of seed mass on performance of seedlings of Artocarpus heterophyllus L. (Moraceae), a large evergreen late successional shade-tolerant tree species in three contrasting light conditions. Seed mass varied many fold from 1.5 to 14 g in A. heterophyllus. Germination and germination time showed a significant correlation with seed mass. Germination differed significantly among three light regimes (50%, 25% and 3%). Seed mass and light level significantly affected seedling survival. The seedlings that emerged from large seeds survived better than those from small seeds under all light regimes. Survival of seedlings was maximum in 25% light regime for all seed mass classes but did not differ significantly from that at 50% light regime. Survival was significantly lower in 3% light as compared to 50% and 25% light regimes. Seedling vigor (expressed in terms of seedling height, leaf area and dry weight) was also significantly affected by seed mass and light regimes. Seedlings that emerged from larger seeds and grew under 50% light regime produced the heaviest seedlings, while those resulting from smaller seeds and grown under 3% light regime produced the lightest seedlings. Resprouting capacity of seedlings after clipping was significantly affected by seed mass and light regime. Seedlings emerging from larger seeds were capable of resprouting several times successively. Resprouting was more pronounced under 50% and 25% light regimes as compared to 3% light. Success of A. heterophyllus regeneration appears to be regulated by an interactive effect of seed mass and light regime.

The impact of grazing intensity on soil characteristics of Stipa grandis and Stipa bungeana steppe in northern China (autonomous region of Ningxia)

Abstract: The effects of grazing intensity on selected soil characteristics in the feather-grass steppes of the autonomous region of Ningxia (northern China) were investigated by a comparison of non-grazed areas (grazing intensity 0), slightly grazed areas (grazing intensity I), moderately grazed areas (II), intensively grazed areas (III) and over-grazed areas (IV). Even in areas used only minimally for grazing activities (I), a serious increase (doubling) in soil hardness was apparent in the upper soil layer. A continual decrease in organic matter in the surface soil can be correlated directly to soil compaction. The content of organic matter in soil of degree IV amounts to only a third of the organic matter found in non-grazed areas. This decrease can be attributed partly to the poor living conditions for soil organisms in compacted soils, but also to a significant reduction in litter. This is because intensive grazing causes reduced vegetation cover leading to litter being blown away by wind or washed away by heavy rainfall. Thus in level III hardly any plant litter remained to be incorporated into the soil as humus. Likewise root density also suffered its largest decrease in areas with a grazing intensity level III. With regard to the content of nitrogen and phosphorous (total and available) hardly any difference between soils of grazing intensity 0 and I was observed, whereas a noticeable decrease was apparent between levels I and II. Available Potassium was similar for all grazing levels. The pH-value of the soil solution is not significantly affected by grazing. We did not observe differences in the soils of the two main types of steppe vegetation (Stipa grandis and Stipa bungeana steppe) in response to grazing. Only the amount of litter in the S. grandis-steppe in non-grazed or slightly grazed areas is noticeably higher than in the S. bungeana steppe.

Comparing predictions of extinction risk using models and subjective judgement

Abstract: Models of population dynamics are commonly used to predict risks in ecology, particularly risks of population decline. There is often considerable uncertainty associated with these predictions. However, alternatives to predictions based on population models have not been assessed. We used simulation models of hypothetical species to generate the kinds of data that might typically be available to ecologists and then invited other researchers to predict risks of population declines using these data. The accuracy of the predictions was assessed by comparison with the forecasts of the original model. The researchers used either population models or subjective judgement to make their predictions. Predictions made using models were only slightly more accurate than subjective judgements of risk. However, predictions using models tended to be unbiased, while subjective judgements were biased towards over-estimation. Psychology literature suggests that the bias of subjective judgements is likely to vary somewhat unpredictably among people, depending on their stake in the outcome. This will make subjective predictions more uncertain and less transparent than those based on models. (C) 2004 Elsevier SAS. All rights reserved.

Role of antioxidant defense system and biochemical adaptation on stress tolerance of high mountain and steppe plants

Abstract: Eleven species were collected from Northwest Anatolian mountains (1500–2000 m) and 18 species were collected from the Central Anatolian steppes (850–1000 m) in June 1998 and 1999 In all the species investigated, the water and dry matter percentages and solute contents were measured The chlorophyll, β-carotene, ascorbate and α-tocopherol contents and catalase (CAT), superoxide dismutase (SOD) and glutathione reductase (GR) enzyme activities of the plants were also determined The steppe plants had lower water content compared with alpine plants The chlorophyll contents of the plants investigated did not change with altitude However, the carotenoid/chlorophyll ratio of alpine plants was found to be significantly higher The antioxidant/chlorophyll ratio of the trees and shrubs was higher than that of herbaceous plants Carotenoid concentrations and SOD activity were higher in alpine plants than in steppe plants Proline and soluble protein concentrations were significantly higher in alpine plants than in steppe plants There was a significant difference between the plants as regards to antioxidant capacity at the family level Though there was a high antioxidant capacity in alpine Poaceae, Lamiaceae species from steppe had very low concentrations of antioxidants In conclusion, it was shown that although antioxidant protection was important in alpine plants, there were significant differences among the plant species In addition to antioxidant protection, the higher soluble protein and proline contents have a very important role in the stress resistance of the alpine plants

Light, nutrients and the growth of herbaceous forest species

Abstract: The herb layer of forests planted on former agricultural land often differs from that of old-growth forest. This study investigates if the expected increased nutrient availability in the shaded conditions of newly planted forests and the plasticity of the species to adjust their biomass allocation to different levels of light and nutrients help to explain these differences in the herb layers of the two forest types. In a greenhouse experiment biomass distribution and production of two species characteristic for the highly shaded forest floor, Circaea lutetiana and Mercurialis perennis , and two species more common in the forest-edge, Aegopodium podagraria and Impatiens parviflora were studied at different levels of light (2%, 8% and 66% of the full light level) and nutrients (30 and 300 kg N ha –1 per year). The main factor affecting allocation and biomass production was light availability. Nutrient supply only had a significant effect at the higher light levels. Species were mainly plastic to changes in light and the two species from the forest floor showed to be more rigid in allocation pattern than the species from the forest-edge. So, although the species from the forest-edge were more plastic, they did not profit from the increased nutrient supply because the main factor affecting biomass distribution and production was light availability.

Evidence that creation of a Pinus radiata plantation in south-eastern Australia has reduced habitat for frogs

Abstract: Loss and fragmentation of habitat resulting from the clearing of forests for agriculture and urban development threaten the persistence of thousands of species worldwide. The clearing of native forest to plant a monoculture of exotic trees may also reduce and fragment the habitat available for indigenous plants and animals. Metacommunity theory suggests that the species richness of a community in a patch of habitat will increase with patch size but decrease with patch isolation. We investigated whether replacement of native Eucalyptus forest with a plantation of Pinus radiata has reduced and fragmented habitat for frogs, leading to a lower species richness of frog communities in the pine plantation and in small and/or isolated remnant patches of native forest. We surveyed frogs at 60 sites at streams and wetlands in the pine plantation, remnant patches of native forest surrounded by pines, and adjacent areas of contiguous native forest near Tumut in New South Wales, Australia. Only two of eight species of frogs were recorded in the pine plantation, and regression modelling indicated that streams and wetlands in the pines supported fewer frog species than those in remnant patches or the intact native forest. In addition, species richness tended to be higher at wide, shallow swamps and marshes near the headwaters of streams, with herbs, grasses, shrubs, reeds, sedges and rushes in the emergent and fringing vegetation. There was little evidence to suggest that larger eucalypt remnants supported more species of frogs, or that remnants isolated by greater expanses of pines supported fewer species, but we had low power to detect these effects with our data set. Our results support the preservation of all remnants of native forest along drainage lines and around swamps, soaks and bogs, regardless of size. Where new pine plantations are established, for example, on cleared agricultural land, care should be taken to maintain the structural and vegetative characteristics of water bodies to ensure that they continue to provide suitable breeding habitat for frogs.

Poor sexual reproduction on the distribution limit of the rare tree Sorbus torminalis

Abstract: Plants growing in small fragmented populations under stressful environmental conditions may have reduced sexual reproduction. This can cause low gene flow between populations and eventually extinction. Here we report on a pollination experiment with Sorbus torminalis, a rare fleshy-fruited tree with a submediterranean distribution in Europe. At the northern limit of its range in SE-Denmark two relatively small and isolated populations were studied for effects of seven pollination treatments on fruit production and on the timing of fruit abortion. There was evidence that lack of pollination and spontaneous self-pollination caused particularly high fruit abortion, which indicates that apomixis is unlikely and spontaneous self-pollination not efficient. Fruit abortion was delayed after hand pollination, which suggests limitation by pollen quantity. Self-pollination caused earlier abortion than experimental cross-pollination within or between populations indicating inbreeding depression. There was no evidence for outbreeding depression as measured by fruit abortion. We conclude that generative reproduction of S. torminalis is reduced on its northern distribution limit and that it might be negatively affected by pollen limitation and inbreeding effects, which have not been compensated for by increased self-compatibility or apomixis.

Population viability analysis based on combining Bayesian, integrated, and hierarchical analyses

Abstract: Several methods used in fisheries stock assessment models that can be applied to population viability analysis are presented. (1) Integrated analysis allows the use of all information on a particular population, and ensures that all model assumptions and parameter are consistent throughout the analysis, that uncertainty is propagated throughout the analysis, and that the correlation among parameters is preserved. (2) Bayesian analysis allows for the inclusion of prior information, and is a convenient way to represent uncertainty. (3) Random-effects models based on hierarchical modeling allow information to be shared among parameter estimates and allow the separation of process error from estimation error. (4) Non-parametric representation of parameters allows for a more flexible relationship among the parameters. (5) Robust likelihood functions provide an automatic method to reduce the influence of outliers when the data sets are large. These methods are applied to artificial data sets provided by the Extinction Risk Working Group of the National Center for Ecological Analysis and Synthesis (NCEAS) using AD Model Builder software (Otter Research™).

Do seed mass and family affect germination and juvenile performance in Knautia arvensis?A study using failure-time methods

Abstract: Germination and seedling establishment are vulnerable stages in the plant life cycle. We investigated how seed mass and family (progeny origin) affect germination and juvenile performance in the grassland herb Knautia arvensis. Seeds were produced by cross-pollination by hand. The fate of 15 individually weighed seeds from each of 15 plants was followed during a 3-month growth chamber experiment. Progeny origin affected germination, both through seed mass and as an independent factor. Two groups of progenies could be distinguished by having rapid or delayed germination. The two groups had similar mean seed masses, but a positive relationship between seed mass and germination rate could be established only among the rapidly germinating progenies. These biologically relevant patterns were revealed because timing of germination was taken into account in the analyses, not only frequencies. Time-to-event data were analysed with failure-time methods, which gave more stable estimates for the relation between germination and seed mass than the commonly applied logistic regression. Progeny origin and seed mass exerted less impact on later characters like juvenile survival, juvenile biomass, and rosette number. These characters were not affected by the timing of germination under the competition-free study conditions. The decrease in the effect of progeny origin from the seed and germination to the juvenile stages suggests that parental effects other than those contributing to the offspring genotype strongly influenced the offspring phenotype at the earliest life stages. Further, the division of progeny germination patterns into two fairly distinct groups indicates that there was a genetic basis for the variation in stratification requirements among parental plants. Field studies are needed to elucidate effects of different timing of germination in the seasonal grasslands that K. arvensis inhabits.

Effects of microhabitat on palm seed predation in two forest fragments in southeast Brazil

Abstract: The establishment of plants depends crucially on where seeds are deposited in the environment Some authors suggest that in forest understory seed predation is lower than in gaps, and higher than at the forest edge However, most studies have been carried out in large forest patches and very little is known about the effects of microhabitat conditions on seed predation in forest fragments We evaluated the effects of three microhabitats (gaps, forest edge, and understory) on seed predation of two palm species (Euterpe edulis and Syagrus romanzoffiana) in two semi-deciduous forest fragments (230 and 2100 ha) in southeast Brazil Our objective was to test two hypotheses: (1) Low rodent abundance in small fragments as a result of meso-predator action levels leads to lower seed predation in small fragments (2) Most mammal species in small fragments are generalists with respect to diet and habitat, so that seed predation is similar in different microhabitats (gaps, forest edge and understory) in the small fragment, but not in the larger one The study community of small fragments is usually composed of generalist species (in diet and habitat aspects), so we expected the same rate of seed predation among microhabitats (gaps, forest edge and understory) in the tested smaller fragment The experiment was carried out in the dry season (for E edulis) and in the wet season (for S romanzoffiana) in 1999 We conclude that post-dispersal seed predation in forest fragments can be directly connected with mammal communities, reflecting their historical and ecological aspects

Life-history traits of alien and native senecio species in the Mediterranean region

Abstract: Two related shrubs, Senecio inaequidens and S. pterophorus, both introduced to western Mediterranean Europe from South Africa, were compared with a native Mediterranean shrub, S. malacitanus, to identify life-history traits that confer invasive ability. We examined ecological interactions that affect seedling emergence and establishment, flowering time, growth and reproduction and competitive ability in these three closely related species. Seeds were planted, the seedlings were then transplanted and individual performance was evaluated with respect to: (1) competition with plant neighbours and (2) resource addition. Senecio inaequidens had higher rates of seedling establishment and a shorter pre-reproductive period. Competition with neighbours had a considerable impact on S. malacitanus, delaying flowering time and reducing growth and reproduction. S. pterophorus showed inefficient seedling establishment compared to the other two species, but performed better in terms of growth and reproduction. The two alien species were markedly more competitive than the native one. However, differences in competitiveness among S. malacitanus and the two aliens varied depending on resource availability. Thus, Senecio inaequidens and S. pterophorus were more affected by competition in subplots with resource addition and by competition in those without addition, respectively. The latter showed a greater capacity to respond to additional resources in competitive environments and, in addition, its reproductive effort was unrelated to habitat conditions. The invasive potential of the alien species was higher than that of the native. This was a result of various biological characteristics and specific interactions between invader and environment, which made the invasiveness of alien species unpredictable.

Ingestion and dispersal: direct and indirect effects of frugivores on seed viability and germination of Corema album (Empetraceae)

Abstract: The effect of gulls, blackbirds and rabbits on the viability and germination ofCoremaalbum seeds are compared. Frugivores can affect seed viability and germination (1) directly, through the effect of ingestion and (2) indirectly, dispersing seeds to different sites with different conditions. These two major factors in the quality of a seed disperser are not necessarily concordant in direction and magnitude. Gulls and blackbirds have similar direct effects, being much better than those of rabbits, due to the low probability of germination of seeds within rabbit pellets. Seed germination occurs mainly in the open ground, particularly in the sparse scrub, and is very low under vegetation cover. This pattern becomes crucial determining the indirect effects of seed dispersers that will depend on their capacity to carry seeds to the most suitable sites for germination. Gulls and rabbits disperse most of seeds to open ground, exerting a positive indirect effect on germination, whereas blackbirds disperse seeds mainly under shrubs, thus exerting a negative indirect effect. Direct and indirect effects on seed germination are concordant for gulls but discordant for blackbirds and rabbits. Gulls were the best dispersers; the overall probability of germination for a seed dispersed by gulls was 17.59%. The quality of blackbirds and rabbits was relatively low (3.49% and 1.17%, respectively). Frugivores seem to be essential for germination of C. album seeds, not as much for their direct effects but for their ability to carry seeds to suitable sites. © 2004 Elsevier SAS. All rights reserved.

Feast and famine: previous defoliation limiting survival of pine processionary caterpillar Thaumetopoea pityocampa in Scots pine Pinus sylvestris

Abstract: This study analyses the consequences of previous defoliation on the survival of the larvae of the pine processionary moth Thaumetopoea pityocampa (Denis and Schiffermuller) feeding on relict Scots pine Pinus sylvestris (L.) ssp. nevadensis Christ in the Sierra Nevada mountains (SE Spain). Egg batches of the pine processionary moth were placed on four groups of Scots pines that underwent different periods of herbivory. The larval survival was related to the nitrogen content, fibre, phenolics and terpenes in the needles. Larval survival was higher in undefoliated pines, lower in pines defoliated two consecutive years, and intermediate in pines defoliated only one year, suggesting a direct relationship between previous defoliation and larval survival. In contrast, none of the characteristics of the needles showed a clear relationship with larval survival. The resulting reduction in larval number also affects the capacity of the larvae to develop during winter, because it hampered nest warming. Thus, previous defoliation limits, although it does not impede, the possibility of repeated defoliation on Scots pine.

Capturing expert knowledge for threatened species assessments: a case study using NatureServe conservation status ranks

Abstract: Assessments for assigning the conservation status of threatened species that are based purely on subjective judgements become problematic because assessments can be influenced by hidden assumptions, personal biases and perceptions of risks, making the assessment process difficult to repeat. This can result in inconsistent assessments and misclassifications, which can lead to a lack of confidence in species assessments. It is almost impossible to understand an expert’s logic or visualise the underlying reasoning behind the many hidden assumptions used throughout the assessment process. In this paper, we formalise the decision making process of experts, by capturing their logical ordering of information, their assumptions and reasoning, and transferring them into a set of decisions rules. We illustrate this through the process used to evaluate the conservation status of species under the NatureServe system (Master, 1991). NatureServe status assessments have been used for over two decades to set conservation priorities for threatened species throughout North America. We develop a conditional point-scoring method, to reflect the current subjective process. In two test comparisons, 77% of species’ assessments using the explicit NatureServe method matched the qualitative assessments done subjectively by NatureServe staff. Of those that differed, no rank varied by more than one rank level under the two methods. In general, the explicit NatureServe method tended to be more precautionary than the subjective assessments. The rank differences that emerged from the comparisons may be due, at least in part, to the flexibility of the qualitative system, which allows different factors to be weighted on a species-by-species basis according to expert judgement. The method outlined in this study is the first documented attempt to explicitly define a transparent process for weighting and combining factors under the NatureServe system. The process of eliciting expert knowledge identifies how information is combined and highlights any inconsistent logic that may not be obvious in subjective decisions. The method provides a repeatable, transparent, and explicit benchmark for feedback, further development, and improvement.

Sex, secondary compounds and asymmetry. Effects on plant–herbivore interaction in a dioecious shrub

Abstract: We analysed the links between herbivory, anthraquinone content and developmental instability of leaves in Rhamnus alpinus, taking into account possible effects of sexual dimorphism. The amount of leaf loss caused by herbivores averaged 3%, rarely exceeding 25%. Leaf losses were evenly distributed in the shrubs, with highest variability among leaves of the same shoot, thus hiding possible shrub, sex or population effects. This pattern of herbivory implies a shifting of caterpillars from one leaf to another before consuming all readily available material. We suggest that this behaviour might be triggered by a short-term change in leaf palatability by means of an increase in the production of secondary compounds. Supporting this hypothesis, we have found a higher anthraquinone content in damaged leaves compared with undamaged ones. The leaves of male plants exhibited a higher concentration of anthraquinones than those of females, which contrasts with classic hypotheses. We relate this to the lower rate of biomass increase in males, which should allow them to allocate more resources to defence. Leaves showed fluctuating asymmetry (FA), but we did not find any relationship between the degree of asymmetry and sex, herbivory or anthraquinone content at any level considered. Therefore, FA cannot be considered as an indicator of susceptibility to damage by herbivores or of the ability to induce the production of defensive compounds in R. alpinus.

Symbiotic mutualism with a community of opportunistic ants: protection, competition, and ant occupancy of the myrmecophyte Barteria nigritana (Passifloraceae)

Abstract: Barteria nigritana is a myrmecophyte tree of Lower Guinea coastal vegetation. Unlike the more specialised B. fistulosa, which harbours a single host-specific mutualistic ant, B. nigritana is associated with several opportunistic ants. Such symbiotic, yet opportunistic, ant–plant associations have been little studied. On 113 clumps of B. nigritana, we censused ant associates and herbivores and compared herbivory on plants occupied by different ants. In addition to these correlative data, protection conferred by different ant species was compared by herbivore-placement experiments. Identity of ant associate changed predictably over plant ontogeny. Pheidole megacephala was restricted to very small plants; saplings were occupied by either Oecophylla longinoda or Crematogaster sp., and the latter species was the sole occupant of larger trees. Damage by caterpillars of the nymphalid butterfly Acraea zetes accounted for much of the herbivory to leaves. Ant species differed in the protection provided to hosts. While P. megacephala provided no significant protection, plants occupied by O. longinoda and Crematogaster sp. suffered less damage than did unoccupied plants or those occupied by P. megacephala. Furthermore, O. longinoda provided more effective protection than did Crematogaster sp. Herbivore-placement experiments confirmed these results. Workers of O. longinoda killed or removed all larval instars of A. zetes. Crematogaster preyed on only the two first larval instars, and P. megacephala preyed mainly on eggs, only rarely attacking the two first larval instars. Opportunistic ants provided significant protection to this relatively unspecialised myrmecophyte. The usual associate of mature trees was not the species that provided most protection.

Effects of habitat and season on removal and hoarding of seeds of wild apricot (Prunus armeniaca) by small rodents

Abstract: The wild apricot (Prunus armeniaca) is widely distributed in the Donglingshan Mountains of Mentougou District of Beijing, China, where its seeds may be an important food resource for rodents. Predation, removal and hoarding of seeds by rodents will inevitably affect the spatio-temporal pattern of seed fate of wild apricot in this area. By marking and releasing tagged seeds of wild apricot, we investigated seeds survival, scatter-hoarding, cache size and seedling establishment, and the preference of micro-habitats used by rodents to store seeds. The results showed that: (1) rodents in this area hoarded food intensively in autumn, as well as in spring and summer. (2) There were significant effects of habitat and season on removal rate of tagged seeds at releasing plots. In both two types of habitats, Low and High shrub, tagged seeds were removed most rapidly by rodents in autumn, at intermediate rates in spring and least rapidly in summer. (3) During three seasons, mean dispersal distance of scatter-hoarded seeds in Low shrub habitat was greater than that in High shrub. Most removed seeds were buried within 21.0 m of the releasing plots. (4) In both two types of habitats, Low and High shrub, rodents tended to carry seeds to US (Under shrub) and SE (Shrub edge) microhabitats for scatter-hoarding or predation. (5) Among the caches made by rodents, most caches contained only one seed, but up to three seeds were observed; caches of 2–3 seeds were common in autumn. (6) By comparing dental marks, we determined that large field mice (Apodemus peninsulae) and David’s rock squirrels (Sciurotamias davidianus) contributed to removal and predation of released tagged seeds. However, only the large field mice exerted a pivotal and positive role on the burial of dispersed seeds. (7) Establishment of three seedlings originated from seeds buried by rodents was documented in High shrub habitat.

A review of protocols for selecting species at risk in the context of US Forest Service viability assessments

Abstract: In December 2000, the USDA Forest Service (USFS) commissioned a review of their process for conducting viability assessments under the National Forest Management Act (NFMA). The objectives of the USFS review were to establish the scientific basis for geographic and temporal scales used in the assessment of viability, to identify and improve approaches that could be used to assess species viability within the context of NFMA, and to describe the strengths and limitations of the approaches used in the viability assessment process. In this paper, we present one aspect of this overall review: methods available and in use for selection of species at risk for the viability assessment process. A representative group of methods includes threatened and endangered species protocols such as the IUCN protocol, the Heritage ranks, the method devised by Millsap et al. (1990) to identify threatened and endangered species in Florida, as well as protocols for narrower taxonomic and geographic ranges. We provide a description of each of the nine protocols reviewed and compare them in terms of their taxonomic and geographic range, biological attributes, consideration of threats and population trends, data requirements, reliability and robustness, transparency and ability to deal with uncertainty. We found that all threatened and endangered species protocols are useful for classifying species at risk, however, those that explicitly include current and future threats are of most use in determining which species will be adversely affected by proposed management actions. We recommend that Heritage ranks be used to identify an initial set of candidate species for assessment of viability considerations, with further refinement and supplementation based on species distributions, relative to the scale of the planning area.

Resprouting after disturbance in the short-lived herb Rorippa palustris (Brassicaceae): an experiment with juveniles

Abstract: The impact of plant age, severity of injury and nutrient levels on the ability to resprout from roots was experimentally assessed in juveniles of the short-lived herb Rorippa palustris (L.) Besser. In a chamber experiment, six cohorts of young plants (1–6 week old) were injured to obtain data on the threshold age for the ability to resprout from roots. We found that plant age was an important factor influencing resprouting ability: injured individuals older than 5 weeks were able to resprout, but not plants younger than 3 weeks. The impact of injury severity (defoliation and removal of axillary buds) and nutrient levels on resprouting ability was assessed on juveniles in a greenhouse experiment. Injury induced growth of new shoots from root buds, while the number of adventitious buds on roots was not influenced by injury. Both injury treatments had a similar effect in this respect, and the amount of regenerated biomass and the extent of regeneration were not different among injury treatments. The number of new shoots produced after injury was higher at the high nutrient level, but the number of formed adventitious buds on roots was not influenced by nutrient level. Nutrient level also influenced the amount of regenerated biomass, but the extent of regeneration (regenerated/removed biomass) was not influenced. The short-lived monocarpic species R. palustris is able to resprout from roots relatively easily. This ability seems to be advantageous in disturbed habitats and this idea is discussed throughout the paper.

Is the interaction between Retama sphaerocarpa and its understorey herbaceous vegetation always reciprocally positive? Competition-facilitation shift during Retama establishment

Abstract: Retama sphaerocarpa is a Mediterranean shrub that when adult, facilitates the establishment of herbaceous plants under its canopy. We test the hypothesis that during the establishment of R. sphaerocarpa seedlings, the interaction with the herbaceous plants is negative. We carried out a greenhouse experiment in which seedlings of R. sphaerocarpa were grown under different conditions of competition with herbs, watering and date of emergence. Measurements of seedling mortality, biomass and growth were taken during the first growing season. We found a significant relationship between R. sphaerocarpa seedling mortality and competition in early spring, presumably due to higher water demand of herbaceous plants. Generally, presence of herbaceous species, lower availability of water and late emergence had negative effects on biomass and growth of Retama seedlings. Additional water compensated for the negative effects of competition, except on leaves and cladodes of Retama seedlings, suggesting that other resources, such as light, could be the subject of competition. In contrast, Retama seedlings exerted a positive influence on the herbaceous plants by increasing their survival and biomass, probably as a consequence of the high availability of nutrients provided by the Rhizobia nodules in the roots of Retama seedlings. We concluded that, at the regeneration stage of the shrub, the interaction between the herbaceous vegetation and the shrub is negative for the shrub and positive for the herbs. This suggests a shift from competition to facilitation with age of Retama, as reciprocal positive interactions have been described between herbaceous plants and adult individuals of the shrub. © 2004 Elsevier SAS. All rights reserved.

Rejuvenation of a mountain birch forest by an Epirrita autumnata (Lepidoptera: Geometridae) outbreak

Abstract: In 1955, the mountain birch forest in the Abisko valley of northern Sweden was defoliated by caterpillars of the moth Epirrita autumnata with death of stems of the polycormic trees as a result. Since then, some stands have recovered from surviving trees, producing new shoots while other stands became rejuvenated from basal sprouts. Usually, basal sprouting occurs after the death of whole trees or stems. In this case, extensive basal sprouting occurred in spite of only minor stem mortality. Two associated explanations to these differences were explored: (i) the abundant basal sprouting was caused by more top damage (and, hence, a reduced apical dominance) than in stands with less sprouting, (ii) this top damage was caused by a higher caterpillar density in the upper part of trees. Studies made during the outbreak and reported here confirm (i) and reject (ii) by showing that caterpillar densities were lower in the upper part of crowns than in the lower. The more extensive damage in the upper part of crowns may have several explanations. However, a specific sequence of events seemed to produce the rejuvenated stand. The sequence included a severe stress existing before the outbreak (as indicated by a decreased radial stem growth) which was increased by defoliations in two successive years. We, therefore, hypothesize that top dieback was caused by between – and within – stem competition for depleted carbohydrate resources at the expense of tree tops. The contributions of different types of sprouts to the rejuvenation and prerequisites for an outbreak to rejuvenate stands are discussed.