Migrating birds are expected to fly at higher airspeeds when minimizing time rather than energy costs of their migratory journeys. Spring migration has often been suggested to be more time selected than autumn migration, because of the advantage of early arrival at breeding sites. We have earlier demonstrated that nocturnal passerine migrants fly at higher airspeeds during spring compared to autumn, supporting time-selected spring migration. In this study, we test the hypothesis that seasonal airspeeds are modulated differently between short- and long-distance migrants, because of a stronger element of time selection for autumn migration over long distances. In support of this hypothesis, we demonstrate that the seasonal difference in airspeed is significantly larger (spring airspeed exceeding autumn airspeed by a factor of 1.16 after correcting for the influence of altitude, wind and climb/descent on airspeed) among short-distance compared to long-distance (factor 1.12) migrants. This result is based on a large sample of tracking radar data from 3 years at Falsterbo, South Sweden. Short-distance migrants also tend to fly with more favourable winds during autumn, indicating relaxed time constraints (being able to afford to wait for favourable winds) compared to long-distance migrants. These results indicate surprisingly fine-tuned seasonal modulation of airspeed and responses to wind, associated with behavioural strategies adapted to different levels of time selection pressures during spring and autumn migration. 相似文献
The margin of safety (MOS) approach is an increasingly prevalent tool for ensuring the integrity of market-based programs for providing ecosystem services. Over-crediting is reduced by setting aside mean estimates of uncertain services in favor of a more conservative estimate. Like many environmental policy problems, ecosystem service markets involve the aggregation of uncertainty over multiple scales, e.g. from landowners to market intermediaries to the overall market. We examine how the MOS instrument affects, and is affected by, an ecosystem services market. We show that the common bottom-up approach of imposing risk preferences at a local, disaggregated level—held over from earlier development in the context of toxics and command and control-style health risk regulation—leads to several unintended consequences. Furthermore, discounting landowner services can actually increase their profits, conditional on the elasticity of credit demand. We illustrate theoretical insights with an empirical application to greenhouse gas offset crediting in agriculture. 相似文献
Spatiotemporal distribution patterns in relation to feeding behavior of herbivorous gastropods have been studied extensively,
but still knowledge about small-scale patterns is limited in relation to eutrophication. This experimental study aimed to
describe the small-scale distribution of Littorina littorea in nutrient-enriched and nutrient-unenriched mesocosms in a merely atidal region and relate the distribution to food abundance
and possible competing organisms, while checking simultaneously for feeding activities. The latter part was accomplished through
the “gut fluorescence technique” GFT (which, to our knowledge, has not previously been used for benthic grazers) to estimate
per capita grazing rates and the former part through monitoring of spatial heterogeneity of L. littorea and co-variation with sessile organisms (using semivariograms and cross-semivariograms, respectively). After 5 months of
nutrient addition, the abundance and biomass of L. littorea had increased in enriched systems, which also had significantly higher total biomass of green algae. Gut pigment content
was higher in L. littorea from enriched mesocosms, and gut depletion rate was higher in L. littorea from unenriched mesocosms. Spatial analysis showed that L. littorea exhibited generally random patterns (suggesting feeding activities) but sometimes (often in the morning) spatial patchiness
(clumped distribution) in both enriched and unenriched conditions. There was mainly positive co-variation between L. littorea and biofilm, while different nutrient conditions exhibited contrasting co-variation between L. littorea and barnacles (positive co-variation in enriched and negative co-variation in unenriched mesocosms). The study offered insights
into how feeding behavior and spatial distribution of a species may interact with community components differently under different
nutrient regimes. The applied methodology can be useful for purposes of faster examination of grazing effects among different
regions and also to compare grazing intensities and interactions between grazers and the benthic communities in disturbed
(including pollution and nutrient enrichment) and non-disturbed systems, as well as in up-welling versus non-upwelling areas. 相似文献
The factors that determine species' range limits are of central interest to biologists. One particularly interesting group comprises odonates (dragonflies and damselflies), which show large differences in secondary sexual traits and respond quickly to climatic factors, but often have minor interspecific niche differences, challenging models of niche-based species coexistence. We quantified the environmental niches at two geographic scales to understand the ecological causes of northern range limits and the coexistence of two congeneric damselflies (Calopteryx splendens and C. virgo). Using environmental niche modeling, we quantified niche divergence first across the whole geographic range in Fennoscandia, and second only in the sympatric part of this range. We found evidence for interspecific divergence along the environmental axes of temperature and precipitation across the northern range in Fennoscandia, suggesting that adaptation to colder and wetter climate might have allowed C. virgo to expand farther north than C. splendens. However, in the sympatric zone in southern Fennoscandia we found only negligible and nonsignificant niche differences. Minor niche differences in sympatry lead to frequent encounters and intense interspecific sexual interactions at the local scale of populations. Nevertheless, niche differences across Fennoscandia suggest that species differences in physiological tolerances limit range expansions northward, and that current and future climate could have large effects on the distributional ranges of these and ecologically similar insects. 相似文献
Physical and biological disturbances are ecological processes affecting patterns in biodiversity at a range of scales in a variety of terrestrial and aquatic systems. Theoretical and empirical evidence suggest that effects of disturbance on diversity differ qualitatively and quantitatively, depending on levels of productivity (e.g., the dynamic equilibrium model). In this study we contrasted the interactive effects between physical disturbance and productivity to those between biological disturbance and productivity. Furthermore, to evaluate how these effects varied among different components of marine hard-substratum assemblages, analyses were done separately on algal and invertebrate richness, as well as richness of the whole assemblage. Physical disturbance (wave action) was simulated at five distinct frequencies, while biological disturbance (grazing periwinkles) was manipulated as present or absent, and productivity was manipulated as high or ambient. Uni- and multivariate analyses both showed significant effects of physical disturbance and interactive effects between biological disturbance and productivity on the composition of assemblages and total species richness. Algal richness was significantly affected by productivity and biological disturbance, whereas invertebrate richness was affected by physical disturbance only. Thus, we show, for the first time, that biological disturbance and physical disturbance interact differently with productivity, because these two types of disturbances affect different components of assemblages. These patterns might be explained by differences in the distribution (i.e., press vs. pulse) and degree of selectivity between disturbances. Because different types of disturbance can affect different components of assemblages, general ecological models will benefit from using natural diverse communities, and studies concerned with particular subsets of assemblages may be misleading. In conclusion, this study shows that the outcome of experiments on effects of disturbance and productivity on diversity is greatly influenced by the composition of the assemblage under study, as well as on the type of disturbance that is used as an experimental treatment. 相似文献
Information on benthic carbon mineralization rates is often derived from the analysis of oxygen microprofiles in sediments. To enable a direct comparison of different sediment environments, it is often desirable to characterize sediments by a single proxy that expresses their “reactivity” towards oxygen. For this, there are three commonly used proxies: the oxygen penetration depth (OPD), the oxygen flux at the sediment-water interface (DOU), and the maximum volumetric oxygen consumption rate (Rmax). The OPD can be directly determined from the oxygen depth profile, while the DOU is usually obtained by a linear fit to the oxygen gradient either in diffusive boundary layer. The oxygen consumption rate Rmax requires the fitting of a reactive-transport model to the data profile. This article shows that the OPD alone is a suboptimal proxy, because it shows a strong dependence on the half-saturation constant Ks, and secondly, because it is sensitive to the particular re-oxidation conditions right above the oxic-anoxic interface. Similarly, the volumetric oxygen consumption rate Rmax is rather strongly dependent on the kinetic model formulation employed. To show this we fitted three different (Bouldin, Blackman and Monod) kinetics to the same oxygen data profiles. When fitting these models, the Rmax values obtained differed by 20% for exactly the same oxygen profile. Accordingly, if one reports Rmax values, it is crucial to specify the kinetic model alongside. Overall, DOU emerges as sediment reactivity proxy which is the least model dependent. 相似文献
Using tracking radars, we investigated the variability of flight directions of long-distance nocturnal passerine migrants
across seasons (spring versus autumn migration) and sites at the southern (56° N) and northern (68° N) ends of the Scandinavian
Peninsula (Lund versus Abisko). Whilst most migrants at Lund are on passage to and from breeding sites in Fennoscandia, the
majority of the migrants at Abisko are close to their breeding sites, and migration at Abisko thus to a large degree reflects
initial departure from breeding sites (autumn) or final approach to breeding destinations (spring). The radar data were used
to test predictions about differences in orientation and wind drift effects between adult and juvenile birds (a large proportion
of autumn migrants consists of juvenile birds on their first journey), between situations far away from or near the goals
and between different phases of migration (initial departure, en route passage, final approach to goal). The concentrations
(both total and within-night concentrations) of flight directions differed significantly between seasons as well as sites,
with the highest concentration at Lund in spring (mean vector length of track directions, r = 0.79) and lowest at Abisko during spring (r = 0.35). Partial wind drift and partial compensation were recorded at Lund, with a similar effect size in spring and autumn,
whilst possible wind drift effects at Abisko were obscured by the large directional scatter at this site. The results from
Lund support the prediction that the high proportion of juveniles in autumn contributes to increase the directional scatter
during this season, whilst there was no support for predictions of differential wind drift effects between seasons and situations
with different goal distances. The most striking and surprising result was the exceedingly large scatter of flight directions
at Abisko, particularly in spring. We suggest that such an exaggerated scatter may be associated with final approach orientation,
where migrants reach their specific goals from all various directions by final navigation within a more wide-ranging goal
region. The larger scatter of autumn flight directions at Abisko compared to Lund may be due to exploratory flights in variable
directions being more common at initial departure from breeding sites than later during migratory passage. These surprising
results highlight the importance of studying and analysing orientation during final approach to (and initial departure from)
migratory goals for understanding the orientation systems of migratory birds. 相似文献
Many South African populations of the brown mussel Perna perna have been depleted through over-exploitation by subsistence harvesters. This is problematic because recovery after disturbance
is very slow, partly because recruits are largely associated with adult mussels. However, unlike large recruits of 3.5–10 mm
that exhibit spatial structure related to that of adults, a very high proportion of settlers and small recruits (0–3.5 mm)
occur on foliose algae. We tested the hypothesis that recruits on algae move to adult mussel beds after a period of growth,
with the null hypothesis that they die at a certain size. We conducted an indirect field study comparing the ratios of large
to small recruits in 100% cover mussel patches at locations with high and low algal cover. A second laboratory experiment
analysed whether the size of recruits on algae affects their active movement behaviour in response to nearby mussel patches.
Large/small recruit ratios were slightly, but not significantly greater in high than low algal cover locations. Both small
(2–2.5 mm) and medium (4.5–5.5 mm) recruits remained on algae and moved very short distances throughout the laboratory experiment,
while larger recruits (9–10 mm) moved significantly further distances and more often into mussel patches. The results suggest
that very large recruits are able to migrate actively to nearby mussel patches, indicating ontogenetic shifts in this behaviour.
However, the absence of a significant difference in ratios between field locations with high and low algal cover suggests
many large recruits are accidentally dislodged from the algae and presumably die. Thus settlement of P. perna onto algae is likely to be wasted, with consequences for sustainable management of the mussel resource. 相似文献
Parental care is a costly part of reproduction. Hence, natural selection should favor males which avoid caring for unrelated
young. However, the decision to abandon or reduce care requires cues which are evaluated to give information on potential
reproductive value of the offspring. The prediction that male sand gobies, Pomatoschistus minutus, care for foreign eggs as long as they were spawned in their own nest and at least some of such cues are fulfilled was tested.
Egg-guarding males that had recently taken part in a spawning event were given a clutch of eggs that was sired either by themselves
or another male, in either their own or another male’s aquarium. Males that had not taken part in a spawning event were used
as controls and were given eggs sired by another male. We measured the amount of filial cannibalism and nest building. Control
group males did not care for eggs and ate them all before rebuilding the nest. In the other treatments, there were no significant
effects of paternity, though males moved to another male’s aquarium increased their clutch area threshold and completely consumed
larger clutches than males that were not moved. There was no intermediate response in any treatment in the form of increased
partial filial cannibalism or less well-constructed nests. Our results suggest that egg-guarding males cannot distinguish
between eggs sired by themselves and those sired by other males but are able to react to cues indicating paternity state.
Males do not adopt eggs to attract females in P. minutus. 相似文献
The multi-scale approach to conserving forest biodiversity has been used in Sweden since the 1980s, a period defined by increased reserve area and conservation actions within production forests. However, two thousand forest-associated species remain on Sweden’s red-list, and Sweden’s 2020 goals for sustainable forests are not being met. We argue that ongoing changes in the production forest matrix require more consideration, and that multi-scale conservation must be adapted to, and integrated with, production forest development. To make this case, we summarize trends in habitat provision by Sweden’s protected and production forests, and the variety of ways silviculture can affect biodiversity. We discuss how different forestry trajectories affect the type and extent of conservation approaches needed to secure biodiversity, and suggest leverage points for aiding the adoption of diversified silviculture. Sweden’s long-term experience with multi-scale conservation and intensive forestry provides insights for other countries trying to conserve species within production landscapes.