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201.
Climatic warming is associated with organisms breeding earlier in the season than is typical for their species. In some species, however, response to warming is more complex than a simple advance in the timing of all life history events preceding reproduction. Disparities in the extent to which different components of the reproductive phenology of organisms vary with climatic warming indicate that not all life history events are equally responsive to environmental variation. Here, we propose that our understanding of phenological response to climate change can be improved by considering entire sequences of events comprising the aggregate life histories of organisms preceding reproduction. We present results of a two-year warming experiment conducted on 33 individuals of three plant species inhabiting a low-arctic site. Analysis of phenological sequences of three key events for each species revealed how the aggregate life histories preceding reproduction responded to warming, and which individual events exerted the greatest influence on aggregate life history variation. For alpine chickweed (Cerastium alpinum), warming elicited a shortening of the duration of the emergence stage by 2.5 days on average, but the aggregate life history did not differ between warmed and ambient plots. For gray willow (Salix glauca), however, all phenological events monitored occurred earlier on warmed than on ambient plots, and warming reduced the aggregate life history of this species by 22 days on average. Similarly, in dwarf birch (Betula nana), warming advanced flower bud set, blooming, and fruit set and reduced the aggregate life history by 27 days on average. Our approach provides important insight into life history responses of many organisms to climate change and other forms of environmental variation. Such insight may be compromised by considering changes in individual phenological events in isolation. 相似文献
202.
Chalcraft DR Cox SB Clark C Cleland EE Suding KN Weiher E Pennington D 《Ecology》2008,89(8):2165-2171
Experimental studies demonstrating that nitrogen (N) enrichment reduces plant diversity within individual plots have led to the conclusion that anthropogenic N enrichment is a threat to global biodiversity. These conclusions overlook the influence of spatial scale, however, as N enrichment may alter beta diversity (i.e., how similar plots are in their species composition), which would likely alter the degree to which N-induced changes in diversity within localities translate to changes in diversity at larger scales that are relevant to policy and management. Currently, it is unclear how N enrichment affects biodiversity at scales larger than a small plot. We synthesized data from 18 N-enrichment experiments across North America to examine the effects of N enrichment on plant species diversity at three spatial scales: small (within plots), intermediate (among plots), and large (within and among plots). We found that N enrichment reduced plant diversity within plots by an average of 25% (ranging from a reduction of 61% to an increase of 5%) and frequently enhanced beta diversity. The extent to which N enrichment altered beta diversity, however, varied substantially among sites (from a 22% increase to an 18% reduction) and was contingent on site productivity. Specifically, N enrichment enhanced beta diversity at low-productivity sites but reduced beta diversity at high-productivity sites. N-induced changes in beta diversity generally reduced the extent of species loss at larger scales to an average of 22% (ranging from a reduction of 54% to an increase of 18%). Our results demonstrate that N enrichment often reduces biodiversity at both local and regional scales, but that a focus on the effects of N enrichment on biodiversity at small spatial scales may often overestimate (and sometimes underestimate) declines in regional biodiversity by failing to recognize the effects of N on beta diversity. 相似文献
203.
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
204.
Christopher M. Brown James D. MacKinnon Amanda M. Cockshutt Tracy A. Villareal Douglas A. Campbell 《Marine Biology》2008,154(3):413-422
Phytoplankton function and acclimation are driven by catalytic protein complexes that mediate key physiological transformations,
including generation of photosynthetic ATP and reductant, and carbon and nitrogen fixation. Quantitation of capacities for
these processes allows estimation of rates for key ecosystem processes, and identification of factors limiting primary productivity.
We herein present molar quantitations of PSI, PSII, ATP synthase, RuBisCO and the Fe protein of nitrogenase of Trichodesmium collected from the Gulf of Mexico, in comparison to determinations for a range of cyanobacteria growing in culture. Using
these measurements, estimates were generated for Trichodesmium capacities for carbon fixation of 1–3.4 g C g chl a
−1 h−1 and nitrogen fixation of 0.06–0.17 g N g chl a
−1 h−1, with diel variations in capacities. ATP synthase levels show that ATP synthesis capacity is sufficient to support these
levels of carbon and nitrogen fixation, and that ATP synthase levels change over the day in accordance with the ATP demands
of nitrogenase and RuBisCO activity. Levels of measured complexes indicate that Trichodesmium manifests n-type diel light acclimation through rapid changes in RuBisCO:PSII, supported by significant investment of cellular nitrogen.
The plasticity in the levels and stoichiometry of these core complexes show that changes in the abundance of core protein
complexes are an important component of acclimation and regulation of metabolic function by Trichodesmium populations.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
205.
Gilad Heinisch Aldo Corriero Antonio Medina Francisco J. Abascal Jose-Miguel de la Serna Robert Vassallo-Agius Antonio Belmonte Ríos Antonio García Fernando de la Gándara Christian Fauvel Christopher R. Bridges Constantinos C. Mylonas Saadet F. Karakulak Isik Oray Gregorio De Metrio Hanna Rosenfeld Hillel Gordin 《Marine Biology》2008,154(4):623-630
Atlantic bluefin tuna (BFT; Thunnus thynnus) is a migrating species straddling the North Atlantic Ocean and Mediterranean Sea. It is assumed that this species is divided
into a western and an eastern stock, which spawn in the Gulf of Mexico and the Mediterranean Sea, respectively. To learn more
about the reproductive behavior of the eastern BFT stock, we tracked gonadal development in adult fish that were sampled between
April and July during three consecutive years (2003–2005). Sampling campaigns were carried out using common fishing methods
at selected locations within the Mediterranean Sea, namely Levantine Sea, Malta, and Balearic Islands. An additional sampling
point, Barbate, was situated northwest of the Straits of Gibraltar along the Atlantic coast. Morphometric parameters such
as the total body mass (M
B) and the weights of the gonads (M
G) were recorded, and the respective gonadosomatic index (GSI) values were calculated. The data collected revealed two important
trends: (1) GSI values are higher in fish caught in the eastern rather than the western locations across the Mediterranean
Sea, and (2) the GSI reaches maximum values between late May and early June in Levantine Sea (eastern Mediterranean Sea),
and only 2 and 4 weeks later in the central (Malta) and western (Balearic Islands) locations, respectively. The advanced gonadal
development in BFT correlates well with higher sea surface temperatures. Our findings also distinguish the northern Levantine
Sea BFT population (mean M
B 78.41 ± 4.13 kg), and the Barbate BFT population with the greatest M
B (all fish sampled > 100 kg). These data reflect a situation in which the eastern Mediterranean basin may function as a habitat
for young BFT, until they gain a larger M
B and are able to move to the Atlantic Ocean. However, the existence of genetically discrete BFT populations in the Mediterranean
Sea cannot be ruled out. 相似文献
206.
Temporal changes in hydrography affect suspended particulate matter (SPM) composition and distribution in coastal systems,
potentially influencing the diets of suspension feeders. Temporal variation in SPM and in the diet of the mussel Perna perna, were investigated using stable isotope analysis. The δ13C and δ15 N ratios of SPM, mussels and macroalgae were determined monthly, with SPM samples collected along a 10 km onshore–offshore
transect, over 14 months at Kenton-on-Sea, on the south coast of South Africa. Clear nearshore (0 km) to offshore (10 km)
carbon depletion gradients were seen in SPM during all months and extended for 50 km offshore on one occasion. Carbon enrichment
of coastal SPM in winter (June–August 2004 and May 2005) indicated temporal changes in the nearshore detrital pool, presumably
reflecting changes in macroalgal detritus, linked to local changes in coastal hydrography and algal seasonality. Nitrogen
patterns were less clear, with SPM enrichment seen between July and October 2004 from 0 to 10 km. Nearshore SPM demonstrated
cyclical patterns in carbon over 24-h periods that correlated closely with tidal cycles and mussel carbon signatures, sampled
monthly, demonstrated fluctuations that could not be correlated to seasonal or monthly changes in SPM. Macroalgae showed extreme
variability in isotopic signatures, with no discernable patterns. IsoSource mixing models indicated over 50% reliance of mussel
tissue on nearshore carbon, highlighting the importance of nearshore SPM in mussel diet. Overall, carbon variation in SPM
at both large and small temporal scales can be related to hydrographic processes, but is masked in mussels by long-term isotope
integration. 相似文献
207.
A Markov model for assessing ecological stability properties 总被引:1,自引:0,他引:1
Ecological systems are frequently modeled as dynamic systems. It is natural then to use the techniques of dynamic systems theory to analyze such models. However, the methods and results that are produced by dynamic systems theory do not always capture the aspects of ecological systems that are of greatest interest to managers and decision-makers. We identify some of the challenges of using dynamic systems theory to explore ecological systems and propose an alternative approach that emphasizes the understanding of transient effects in light of uncertainty and variability. We illustrate this method by an examination of a model for phosphorus levels in fresh water lakes. 相似文献
208.
Hannah W. McKenzie Christopher L. Jerde Darcy R. Visscher Evelyn H. Merrill Mark A. Lewis 《Environmental and Ecological Statistics》2009,16(4):531-546
Global Positioning System (GPS) collars are increasingly used to study animal movement and habitat use. Measurement error
is defined as the difference between the observed and true value being measured. In GPS data measurement error is referred
to as location error and leads to misclassification of observed locations into habitat types. This is particularily true when
studying habitats of small spatial extent with large amounts of edge, such as linear features (e.g. roads and seismic lines).
However, no consistent framework exists to address the effect of measurement error on habitat classification of observed locations
and resulting biological inference. We developed a mechanistic, empirically-based method for buffering linear features that
minimizes the underestimation of animal use introduced by GPS measurement error. To do this we quantified the distribution
of measurement error and derived an explicit formula for buffer radius which incorporated the error distribution, the width
of the linear feature, and a predefined amount of acceptable type I error in location classification. In our empirical study
we found the GPS measurement error of the Lotek GPS_3300 collar followed a bivariate Laplace distribution with parameter ρ = 0.1123. When we applied our method to a simulated landscape, type I error was reduced by 57%. This study highlights the
need to address the effect of GPS measurement error in animal location classification, particularily for habitats of small
spatial extent. 相似文献
209.
Christopher J. Williams Patricia J. Heglund 《Environmental and Ecological Statistics》2009,16(4):495-513
Habitat association models are commonly developed for individual animal species using generalized linear modeling methods
such as logistic regression. We considered the issue of grouping species based on their habitat use so that management decisions
can be based on sets of species rather than individual species. This research was motivated by a study of western landbirds
in northern Idaho forests. The method we examined was to separately fit models to each species and to use a generalized Mahalanobis
distance between coefficient vectors to create a distance matrix among species. Clustering methods were used to group species
from the distance matrix, and multidimensional scaling methods were used to visualize the relations among species groups.
Methods were also discussed for evaluating the sensitivity of the conclusions because of outliers or influential data points.
We illustrate these methods with data from the landbird study conducted in northern Idaho. Simulation results are presented
to compare the success of this method to alternative methods using Euclidean distance between coefficient vectors and to methods
that do not use habitat association models. These simulations demonstrate that our Mahalanobis-distance-based method was nearly
always better than Euclidean-distance-based methods or methods not based on habitat association models. The methods used to
develop candidate species groups are easily explained to other scientists and resource managers since they mainly rely on
classical multivariate statistical methods. 相似文献
210.
Kazuhiro Sonoda J. Alan. Yeakley Christopher E. Walker 《Journal of the American Water Resources Association》2001,37(6):1517-1532
ABSTRACT: We investigated spatial and temporal relationships among surface and subsurface watershed attributes and stream nutrient concentrations in urbanizing Johnson Creek watershed in northern Oregon. We sampled stream water at eight urban and five nonurban locations from March 1998 through December 1999. We sampled eight wells distributed over the two primary aquifers in the watershed. Using a Geographic Information System (GIS), percentages of landuse attributes within a radius of 30, 91, and 152 m from each sample site were quantified. We analyzed relationships between (1) nutrient concentrations and percentage cover of different landuse attributes, and (2) nutrient concentrations and underlying hydrologic units. We did not find a significant relationship between ground water chemistry and stream water chemistry. We found elevated levels of phosphorus (P) concentrations correlated with urban landuse, while higher nitrogen (N) concentrations were correlated with nonurban (primarily agricultural) landuse. We concluded that elevated levels of N in nonurban areas of Johnson Creek watershed were associated with agricultural practices. We further concluded that urban development factors such as increases in storm drains, dry wells, and impermeable surfaces may be responsible for higher input of P to the stream in urbanizing areas of the Johnson Creek watershed. 相似文献