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911.
Habitats vary considerably in the level of invasion (number or proportion of alien plant species they contain), which depends on local habitat properties, propagule pressure, and climate. To determine the invasibility (susceptibility to invasions) of different habitats, it is necessary to factor out the effects of any confounding variables such as propagule pressure and climate on the level of invasion. We used 20 468 vegetation plots from 32 habitats in the Czech Republic to compare the invasibility of different habitats. Using regression trees, the proportion of alien plants, including archaeophytes (prehistoric to medieval invaders) and neophytes (recent invaders), was related to variables representing habitat properties, propagule pressure, and climate. The propagule pressure was expressed as the proportion of surrounding urban and industrial or agricultural land, human population density, distance from a river, and history of human colonization in the region. Urban and industrial land use had a positive effect on the proportion of both archaeophytes and neophytes. Agricultural land use, higher population density, and longer history of human impact positively affected the proportion of archaeophytes. Disturbed human-made habitats with herbaceous vegetation were most invaded by both groups of aliens. Neophytes were also relatively common in disturbed woody vegetation, such as broad-leaved plantations, forest clearings, and riverine scrub. These habitats also had the highest proportion of aliens after removing the effect of propagule pressure and climate, indicating that they are not only the most invaded, but also most invasible. These habitats experience recurrent disturbances and are rich, at least temporarily, in available nutrients, which supports the hypothesis that fluctuating resources are the major cause of habitat invasibility. The least invaded habitats were mires and alpine-subalpine grasslands and scrub. After removing the effect of propagule pressure and climate, some habitats actually invaded at an intermediate level had very low proportions of aliens. This indicates that these habitats (e.g., dry, wet, and saline grasslands, base-rich fens, and broad-leaved deciduous woodlands) are resistant to invasion. 相似文献
912.
Snchez-Piero Joel Gmez-Meijide Paula Concha-Graa Estefana Moreda-Pieiro Jorge Muniategui-Lorenzo Soledad Lpez-Maha Purificacin 《Environmental Chemistry Letters》2022,20(1):49-57
Environmental Chemistry Letters - Polycyclic aromatic hydrocarbons (PAHs) in atmospheric particulate matter have adverse effects on human health, yet total PAH concentrations... 相似文献
913.
914.
The establishment of fighting rules and the ability to recognise individual conspecifics and to assess their fighting ability
and/or roles may help to reduce costs of fighting. We staged encounters between males of the lizard Podarcis hispanica to examine whether lizards used fighting strategies and whether a previous agonistic experience affects the outcome and characteristics
of a subsequent encounter. The results showed that simple rules such as body size differences and residence condition were
used to determine the outcome of agonistic interactions as quickly as possible. Thus, larger males were dominant in most encounters.
However, when size differences between opponents are smaller, they may be more difficult to estimate and, then, residence
condition was more important. In addition, the intensity of interactions between males could be explained according to the
”sequential assessment game”, supporting the idea that P. hispanica males acquire information about fighting ability gradually during the progress of a fight. Our results also showed that the
second fight of the same pair of males was less aggressive, even when its outcome was the opposite of the first. This result
suggests that male P. hispanica can recognise individual opponents and that they use this information to reach a contest outcome more quickly, thus reducing
unnecessary aggression levels in subsequent interactions. These fighting strategies and assessment mechanisms may help to
stabilise the social system of this lizard.
Received: 2 November 1999 / Revised: 26 August 2000 / Accepted: 4 September 2000 相似文献
915.
A. P. Lemes M. A. Soto-Oviedo W. R. Waldman L. H. Innocentini-Mei N. Durán 《Journal of Polymers and the Environment》2010,18(3):250-259
The effect of lignosulfonate on poly(3-hydroxybutyrate-co-3-hydroxyvalerate), PHBV, was studied by scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and
thermogravimetric analysis (TGA). The PHBV/lignosulfonate samples were prepared by melt mixing in an internal mixer. SEM showed
that PHBV/lignosulfonate samples present a cracked surface that is more intense in mixtures with high lignosulfonate proportions.
According to DSC, melting and glass transition temperatures of the PHBV matrix decrease with lignosulfonate addition. The
same effect was observed for melting enthalpies (ΔHm), which indicates a decrease of crystallinity. TGA showed that thermal stability of PHBV/lignosulfonate samples was shifted
to lower temperatures, which indicates the existence of an interaction between the thermal decomposition processes of PHBV
and lignosulfonate. 相似文献
916.
Hugh?DrummondEmail author Cristina?Rodríguez Adriana?Vallarino Claudia?Valderrábano Gabriela?Rogel Emilio?Tobón 《Behavioral ecology and sociobiology》2003,53(5):287-296
According to the desperado sibling hypothesis, chicks of obligately siblicidal species kill their junior broodmates as early as possible because junior broodmates face dire ecological prospects and are consequently predisposed to aggressively overthrow elder broodmates by all-out aggression. The agonistic behavior of junior chicks is virtually unknown because they die so young. We investigated the agonistic behavior of hypothetical desperados by fostering junior brown boobies (Sula leucogaster, an obligately siblicidal species) into nests of the blue-footed booby (S. nebouxii, a facultatively siblicidal species) containing an older singleton blue-foot chick. Controls were junior blue-footed boobies fostered into the same situation. Junior brown boobies were 7 times more aggressive than controls and most of them dominated their elder and larger nestmates. Four of nine brown booby juniors showed relentless aggression, delivering up to 711 pecks, bites and pushes (including "expulsion pushes") per hour, thereby overwhelming nestmates 90% heavier and permanently expelling one of them from the nest. Similarly, in natural broods of two surviving brown booby chicks, the losing chick was 13 times as aggressive as blue-foot subordinates, up to at least age 7 weeks. Contrast of the two species of booby suggests the evolution of agonistic roles within broods may be partly driven by selection on potential victims to express a level and type of aggressiveness appropriate to their status-related ecological prospects. 相似文献
917.
Lead and cadmium levels of some species of brown-algae (Phaeophyta) from the mesolittoral (intertidal area) of the Island of Tenerife (central-eastern Atlantic) were determined by Atomic Absorption Spectrometry. The quality control was carried out using a standard "CRM 279 Ulva lactuca".The mean, minimum and maximum concentrations were 11.21, 2.090 and 81.795 microg/g/dw; and 1.13, 0.190 and 5.130 microg/g/dw for lead and cadmium, respectively. The fact that samples registering the highest cadmium concentrations were the same as those which showed the highest lead level corresponding to a sampling station nearby an urban water outlet could be relevant. 相似文献
918.
919.
Aurora M. Castilla Stefan Van Dongen Anthony Herrel Amadeu Francesch Juan Martínez de Aragón Jim Malone Juan José Negro 《Die Naturwissenschaften》2010,97(2):143-151
We compared membrane thickness of fully developed eggs with those of non-developed eggs in different endangered falcon taxa.
To our knowledge, membrane thickness variation during development has never been examined before in falcons or any other wild
bird. Yet, the egg membrane constitutes an important protective barrier for the developing embryo. Because eggshell thinning
is a general process that occurs during bird development, caused by calcium uptake by the embryo, eggs are expected to be
less protected and vulnerable to breakage near the end of development. Thus, egg membranes could play an important protective
role in the later stages of development by getting relatively thicker. We used linear mixed models to explore the variation
in membrane thickness (n = 378 eggs) in relation to developmental stage, taxon, female age, mass and identity (73 females), egg-laying sequence (105
clutches) and the study zone. Our results are consistent with the prediction that egg membranes are thicker in fully developed
eggs than in non-developed eggs, suggesting that the increase in membrane thickness during development may compensate for
eggshell thinning. In addition, our data shown that thicker membranes are associated with larger, heavier and relatively wider
eggs, as well as with eggs that had thinner eggshells. Egg-laying sequence, female age and the study zone did not explain
the observed variation of membrane thickness in the falcon taxa studied. As we provide quantitative data on membrane thickness
variation during development in falcons not subjected to contamination or food limitation (i.e. bred under captive conditions),
our data may be used as a reference for studies on eggs from natural populations. Considering the large variation in membrane
thickness and the multiple factors affecting on it and its importance in the protection of the embryo, we encourage other
researchers to include measurements on membranes in studies exploring eggshell thickness variation. 相似文献
920.
García-Palacios P Bowker MA Maestre FT Soliveres S Valladares F Papadopoulos J Escudero A 《Ecological applications》2011,21(7):2806-2821
Roadside grasslands undergoing secondary succession are abundant, and represent ecologically meaningful examples of novel, human-created ecosystems. Interactions between plant and soil communities (hereafter plant-soil interactions) are of major importance in understanding the role of biotic control in ecosystem functioning, but little is known about these links in the context of ecosystem restoration and succession. The assessment of the key biotic communities and interactions driving ecosystem development will help practitioners to better allocate the limited resources devoted to roadside grassland restoration. We surveyed roadside grasslands from three successional stages (0-2, 7-9, and >20 years) in two Mediterranean regions of Spain. Structural equation modeling was used to evaluate how interactions between plants, biological soil crusts (BSCs), and soil microbial functional diversity (soil microorganisms) affect indicators of ecosystem development and restoration: plant similarity to the reference ecosystem, erosion control, and soil C storage and N accumulation. Changes in plant community composition along the successional gradient exerted the strongest influence on these indicators. High BSC cover was associated with high soil stability, and high soil microbial functional diversity from late-successional stages was associated with high soil fertility. Contrary to our expectations, the indirect effects of plants, mediated by either BSCs or soil microorganisms, were very weak in both regions, suggesting a minor role for plant-soil interactions upon ecosystem development indicators over long periods. Our results suggest that natural vegetation dynamics effectively improved ecosystem development within a time frame of 20 years in the grasslands evaluated. They also indicate that this time could be shortened if management actions focus on: (1) maintaining well-conserved natural areas close to roadsides to enhance plant compositional changes towards late-successional stages, (2) increasing BSC cover in areas under strong erosion risk, to avoid soil loss, and (3) enhancing soil microbial functional diversity in resource-limited areas, to enhance soil C and N accumulation. 相似文献