Demographic dynamics of Akodon azarae (Cricetidae: Sigmodontinae) in linear habitats of agricultural landscapes of central Argentina

Linear habitats are capable of providing essential resources for small mammals within agroecosystems. We analyzed demographic parameters of Akodon azarae in a linear habitat of central Argentina. We used capture-mark-recapture models to determine temporal variations in survival, recruitment and population growth rate. The effects of temperature, rainfall and vegetation cover as well as of population abundances on the mentioned parameters were assessed in a 10-year study. Survival and growth rate showed seasonal variation, which was greater than the interannual variability observed. Temperature affected only recruitment. Linear habitats would provide resources for long term survival and reproduction of A. azarae.     

Population dynamics of two rodent species in agro-ecosystems of central Argentina: intra-specific competition,land-use,and climate effects

Understanding the role of feedback structure (endogenous processes) and exogenous (climatic and environmental) factors in shaping the dynamics of natural populations is a central challenge within the field of population ecology. We attempted to explain the numerical fluctuations of two sympatric rodent species in agro-ecosystems of central Argentina using Royama’s theoretical framework for analyzing the dynamics of populations influenced by exogenous climatic forces. We found that both rodent species show a first-order negative feedback structure, suggesting that these populations are regulated by intra-specific competition (limited by food, space, or enemy-free space). In Akodon azarae endogenous structure seems to be very strongly influenced by human land-use represented by annual minimum normalized difference vegetation index (NDVI), with spring and summer rainfall having little influence upon carrying capacity. Calomys venustus’ population dynamics, on the other hand, seem to be more affected by local climate, also with spring and summer rainfall influencing the carrying capacity of the environment, but combined with spring mean temperature. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Differential effects of climate,environment, and land use on two sympatric species of Akodon

We describe changes in abundance of two rodent species over a 12-year period and assess the relationship between population abundance, climate, and agricultural practices in southern Córdoba Province, Argentina. We estimated abundance from trapping edges of agricultural areas, railway rights of way, and roadsides. Variables considered were: normalized difference vegetation index (NDVI), surface temperature, minimum and maximum temperature, rainfall, and cultivated areas of different crops. Species abundances varied over time; those of Akodon dolores declined, whereas those of A. azarae increased. Climatic and environmental changes may have had differential influences on species abundances. Autumn abundance of A. dolores was positively related to spring rainfall and area of harvested sorghum, and negatively related to NDVI. Akodon azarae abundance was negatively correlated with winter minimum temperature, spring rainfall, and sorghum harvested area, but positively associated with NDVI. On the other hand, both species were negatively correlated with each other. We suggest that environmental conditions may have changed the competition outcome for Akodon spp., and thus, had direct, differential effect on species abundances.     

NDVI‐based vegetation monitoring in Mau forest complex,Kenya

The normalized difference vegetation index (NDVI) measures vegetation health and density using plant reflectance characteristics recorded by satellite imagery. Dekadal NDVI data were obtained for January 1999–December 2009 from 1‐km resolution SPOT‐VEGETATION sensor for closed woody vegetation type in four blocks of the Mau forest complex. Vegetation response to yearly seasonal variations was plotted and used to compare deviations by specific years. Subnormal vegetation conditions were recorded by the standardized vegetation index (SVI) and persistently low SVI values indicated a drought season or degraded vegetation. The general linear trend of the vegetation was plotted for the study period to identify trends towards degradation or vegetation recovery. Analysis of variance was used to compare forest blocks and shows spatial vegetation variations and also among years to identify vegetation variations with time. Rainfall data recorded for 2002–2009 in east Mau were used to confirm rainfall‐related vegetation variations block. Results show that NDVI patterns within an year follow cyclic trends with a strong dependence on rainfall seasons. The forest vegetation indicated negligible changes over the study period but effects of extended dry periods in 2000 and 2009 were evident. There were significant differences (P < 0.05) in NDVI between forest blocks. East Mau had significantly inferior vegetation that can be attributed to forest type, level of human degradation prior to the study and the lower rainfall. There were significant variations (P < 0.05) of NDVI among years but the forests showed a natural resilience to disturbance and can retain original vegetation vigour once stress is removed. The study proposes further monitoring of the forests including other vegetation types that are more vulnerable to climatic variations and anthropogenic effects.     

A framework for predicting and visualizing the East African wildebeest migration-route patterns in variable climatic conditions using geographic information system and remote sensing

In the Serengeti–Mara ecosystem of East Africa, the migrating wildebeests (Connochaetes taurinus) response to food resource distribution and terrain complexity impacts their movement characteristics. This manifests in varying ways such as movement speed, direction, turning frequency, and moving distance. To investigate these characteristics, indices derived from vegetation quantity (normalized difference vegetation index, NDVI) and relief (slope) were used in our previous work to quantify the relationships between migration route location versus vegetation, relief complexity, and their combination. Least cost pathways determined using these indices were representative of approximate migration routes. The simulated routes were shown to be strongly influenced by vegetation during the dry season. However the impact of climatic change (rainfall) on route location was not investigated though known to influence vegetation recovery patterns. This paper specifically addresses the impact of climatic change on route location. The mean monthly rainfall data were used to classify the rainy and dry seasons in the Serengeti, the Western, and the Mara areas as normal, drier, or wetter than normal, over the 1986–1997 period. The classification is based on the mean monthly rainfall variability about the 11-year seasonal mean. Regression analysis showed strong linear relationships between rainfall and mean NDVI for each one of the three areas. The subsequent seasonal classification based on the corresponding habitat vegetation characteristics (NDVI) revealed the relative variation of vegetation with rainfall. Using the derived general categories, migration routes are then predicted for the various categories using a route attractivity index. The seasonal migration routes were shown to change depending on the relative abundance of the rainfall during the dry season. Dry season migration routes tended toward areas with better vegetation activity, i.e., those characterized by higher NDVI gradients. Our results showed that during the western trek, wetter dry seasons have the effect of delaying the herds movement northwestward. During the northern trek, wetter dry seasons have the effect of delaying the tendency to move westward. However the variation in rainfall conditions during the rainy and dry season had no significant influence on the southern trek route location. We assume that predicted routes based on average general category conditions for different years are representative of main migration route patterns for similar seasons, therefore they are well suited for approximate route prediction, if the climatic characteristics of the year are known.     

Ecological preference between generalist and specialist rodents: spatial and environmental correlates of phenotypic variation

Different ecological preferences among species may result in differences in response to similar environmental variation. To test this hypothesis, we assessed the patterns of skull and mandible size and shape variation in three Sigmodontinae mice from agroecosystems of central Argentina with increasing degree of specialization: Calomys musculinus, Akodon azarae and Oxymycterus rufus. Spatial patterns in size and shape were analysed after controlling for allometry and sexual dimorphism using a total of 697 specimens. We then evaluated the covariation between shape, climatic and environmental variables and assessed the contribution of distinct climatic and environmental variables to phenotypic variability. Oxymycterus rufus displayed a marked spatial structure, and there was a high correlation between shape, climatic and environmental variables in this species. Climatic and environmental variables had a moderate effect on the phenotype of A. azarae, and were not correlated with morphological variation in C. musculinus. Our study highlights the difference in phenotypic responses to spatial and environmental gradients across coexisting species, specialist species displaying a more marked spatial structure in morphology than generalist species. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 112 , 180–203.     

Rangeland vegetation dynamics and moisture availability in Tunisia: an investigation using satellite and meteorological data

Improved knowledge of the interactions between regional climatic patterns and vegetation dynamics are necessary for predicting the future impacts of climate change on vegetation and biogeochemical processes. This paper describes how Normalized Difference Vegetation Index (NDVI) images generated from Advanced Very High Resolution Radiometer (AVHRR) satellite data were used to investigate the dynamics of rangeland vegetation in Tunisia. The NDVI images provided information about intra- and inter-annual variations in vegetation over nine growing seasons (1983–1992). Comparison of the NDVI data with field-collected ecological parameters for nine individual field sites indicated a strong relationship between the NDVI and percentage vegetation cover. The relationship between biomass measurements and NDVI was, however, less strong. Rainfall and NDVI data for each field site were compared, and significant relationships were found between the two. These indicated that there was a delay in the vegetation response to rainfall. In addition, the NDVI data showed that the vegetation at some of the field sites remained active throughout the summer although there was no rainfall during this period. TuMERT (Tunisian Model to Estimate Rangeland Transpiration), a simple water-balance model, was developed to estimate the amount of rainfall available for use by the vegetation during transpiration. The estimates of actual transpiration derived from TuMERT were found to be more strongly correlated with the AVHRR-NDVI measurements than the rainfall data.     

Environmental controls of NDVI dynamics in Patagonia based on NOAA-AVHRR satellite data

Abstract. Variation in vegetation in extra-Andean Patagonia (Argentina) was analyzed using spectral data derived from AVHRR/NOAA satellite. The study of seasonal dynamics of the Normalized Difference Vegetation Index (NDVI, i.e. a combined index of the reflection in the red and infrared bands) highlighted similarities in functional aspects between regional vegetation units which are dissimilar in a geographical, physiognomical and/or floristical way, and also suggested that gross primary production is correlated with mean annual rainfall. The first axis in a Principal Component Analysis of NDVI data was correlated (r² = 0.90) with NDVI as integrated for the study period. The second axis was correlated (r² = 0.50) with the differences in NDVI during the growing season, reflecting seasonality. Mean annual rainfall accounted for 60% of integrated NDVI variability among vegetation units. Much of the residual variance (62%) was accounted for by the inverse of the distance to the Atlantic Ocean, which is interpreted as an ocean effect on vegetation functioning in the extra-Andean Patagonia.     

Satellite‐derived NDVI,LST, and climatic factors driving the distribution and abundance of Anopheles mosquitoes in a former malarious area in northwest Argentina

Distribution and abundance of disease vectors are directly related to climatic conditions and environmental changes. Remote sensing data have been used for monitoring environmental conditions influencing spatial patterns of vector‐borne diseases. The aim of this study was to analyze the effect of the Normalized Difference Vegetation Index (NDVI) and Land Surface Temperature (LST) obtained from the Moderate Resolution Imaging Spectroradiometer (MODIS), and climatic factors (temperature, humidity, wind velocity, and accumulated rainfall) on the distribution and abundance of Anopheles species in northwestern Argentina using Poisson regression analyses. Samples were collected from December, 2001 to December, 2005 at three localities, Aguas Blancas, El Oculto and San Ramón de la Nueva Orán. We collected 11,206 adult Anopheles species, with the major abundance observed at El Oculto (59.11%), followed by Aguas Blancas (22.10%) and San Ramón de la Nueva Orán (18.79%). Anopheles pseudopunctipennis was the most abundant species at El Oculto, Anopheles argyritarsis predominated in Aguas Blancas, and Anopheles strodei in San Ramón de la Nueva Orán. Samples were collected throughout the sampling period, with the highest peaks during the spring seasons. LST and mean temperature appear to be the most important variables determining the distribution patterns and major abundance of An. pseudopunctipennis and An. argyritarsis within malarious areas.     

Remote Sensing of Climatic Anomalies and West Nile Virus Incidence in the Northern Great Plains of the United States

The northern Great Plains (NGP) of the United States has been a hotspot of West Nile virus (WNV) incidence since 2002. Mosquito ecology and the transmission of vector-borne disease are influenced by multiple environmental factors, and climatic variability is an important driver of inter-annual variation in WNV transmission risk. This study applied multiple environmental predictors including land surface temperature (LST), the normalized difference vegetation index (NDVI) and actual evapotranspiration (ETa) derived from Moderate-Resolution Imaging Spectroradiometer (MODIS) products to establish prediction models for WNV risk in the NGP. These environmental metrics are sensitive to seasonal and inter-annual fluctuations in temperature and precipitation, and are hypothesized to influence mosquito population dynamics and WNV transmission. Non-linear generalized additive models (GAMs) were used to evaluate the influences of deviations of cumulative LST, NDVI, and ETa on inter-annual variations of WNV incidence from 2004–2010. The models were sensitive to the timing of spring green up (measured with NDVI), temperature variability in early spring and summer (measured with LST), and moisture availability from late spring through early summer (measured with ETa), highlighting seasonal changes in the influences of climatic fluctuations on WNV transmission. Predictions based on these variables indicated a low WNV risk across the NGP in 2011, which is concordant with the low case reports in this year. Environmental monitoring using remote-sensed data can contribute to surveillance of WNV risk and prediction of future WNV outbreaks in space and time.     

Seasonal variation of microhabitat distribution of the polymorphic land snail Cepaea nemoralis

We studied the seasonal variation of microhabitat distribution of the land snail Cepaea nemoralis over a 3-year period in a population at Dansville, New York. Stratified random quadrat sampling was used to determine snail densities and environmental variables in each month. The plant cover of each quadrat was estimated by a modified Daubenmire measure. Canonical correlation analysis was used to investigate the relationship between the morph density and the environmental variables. Significant relations existed between snail morphs and environmental variables in 8 of the 13 months analyzed. Temperature and rainfall are two important factors affecting such relations. In hot and dry summer months, morphs had a stronger canonical correlation with the environmental variables than in cool and wet months. Food and shelter were important in determining distribution over habitats of the snail. Food was primarily responsible for snail distribution over habitats in the early summer. As the weather became hot and dry, the importance of shelter became more evident. Both banded and unbanded morphs tended to be associated strongly with sheltered microhabitats in hot dry seasons.     

Seasonal Variation in Aboveground Production and Radiation-use Efficiency of Temperate rangelands Estimated through Remote Sensing

Aboveground net primary production (ANPP) of grasslands varies spatially and temporally. Spectral information provided by remote sensors is a promising new tool that may be able to estimate ANPP in real time and at low cost. The objectives of this study were (a) to evaluate at a seasonal scale the relationship between ANPP and the normalized difference vegetation index (NDVI), (b) to estimate seasonal variations in the coefficient of conversion of absorbed radiation into aboveground biomass (ε_a), and (c) to identify the environmental controls on such temporal changes. We used biomass-based field determinations of ANPP for two grassland sites in the Flooding Pampa, Argentina, and related them with NDVI data derived from the NOAA Advanced Very High Resolution Radiometer (AVHRR) satellites using three different models. Results were compared with data obtained from the new Moderate Resolution Imaging Spectroradiometer (MODIS) sensor at an additional site. The first model was based solely on NDVI; the second was based on the amount of photosynthetically active radiation absorbed by the green vegetation (APAR_g), which was derived from NDVI and incoming photosynthetically active radiation (PAR); the third was based on APAR_g and ε_a, which was in turn estimated from climatic variables. NDVI explained between 63 and 93% of ANPP variation, depending on the site considered. Estimates of ANPP were not improved by considering the variation in incoming PAR. At both sites, ε_a varied seasonally (from 0.2 to 1.2 g DM/MJ) and was significantly associated with combinations of precipitation and temperature. Combining ε_a variations with APAR_g increased our ability to account for seasonal ANPP variations at both sites. Our results indicate that NDVI produces good, direct estimates of ANPP only if NDVI, PAR, and ε_a are correlated throughout the seasons. Thus, in most cases, seasonal variations of ε_a associated with temperature and precipitation must be taken into account to generate seasonal ANPP estimates with acceptable accuracy.     

Understanding the role of climatic and environmental variables in gonadal maturation and spawning periodicity of spotted snakehead, <Emphasis Type="Italic">Channa punctata</Emphasis> (Bloch, 1793) in a tropical floodplain wetland,India

Temperature and seasonal rainfall along with other environmental variables are important in regulating the reproductive cycles in teleost fishes. Certain environmental variables may act as cues for reproduction and changes in these may affect seasonality and success of reproduction, as fishes are known to integrate their physiological functions with environmental cycles. Wetlands are sensitive to climate change due to their shallow and confined nature. Since wetlands are important spawning and nursery grounds for many fishes, changes in the environmental variables may have direct consequences for the spawning and survival of fish. In the present study, we have assessed climatic and water chemistry variables capable of influencing seasonality in environmental variables as well as gonadal maturation of spotted snakehead Channa punctata, to predict threshold values of Gonado Somatic Index in females and a favourable range of identified climatic and water chemistry variables for breeding success. Among the climatic and water chemistry variables studied, seasonal variation in rainfall was found to have the most profound effect on gonadal maturation and breeding in C. punctata, followed by water temperature. The favourable range of rainfall obtained varied between 800 mm to 1400 mm, corresponding to the water temperature range between 29 °C and 31 °C. An overall significant warming trend with a reduction in total rainfall has been observed with changes in seasonal trends in temperature and rainfall in the study area. The rainfall being the major climatic factors influencing water chemistry in the wetlands during the spawning season, changes in rainfall pattern may influence breeding periodicity of C. punctata in wetlands in climate change scenario.     

1982-2012年中亚地区植被时空变化特征及其与气候变化的相关分析

干旱区植被生态系统对气候变化极为敏感,并且干旱区的植被变化研究对全球碳循环具有重要意义。然而近几十年来,中亚干旱区植被对气候变化的响应机制尚不甚明朗。利用归一化植被指数NDVI数据集和MERRA（Modern-Era Retrospective Analysis for Research and Applications）气象数据,采用经验正交函数（EOF,Empirical Orthogonal Function）和最小二乘法等方法系统分析了31a（1982-2012年）来中亚地区NDVI在不同时间尺度的时空变化特征。进一步分析和研究NDVI与气温和降水的相关性,结果表明：1982-2012年,中亚地区年NDVI总体呈现缓慢增长趋势,而1994年以后年NDVI呈现明显下降趋势,尤其在哈萨克斯坦北部草原地区下降趋势尤为突出。这可能是由于过去30年间,中亚地区降水累计量的持续减少造成的。NDVI的季节变化表明春季NDVI增长最为明显,冬季则显著下降。与平原区相比,中亚山区的NDVI值增长幅度最大,并且山区年NDVI与季节NDVI呈现显著增加趋势（P < 0.05）。中亚地区年NDVI与年降水量正相关,而年NDVI与气温变化存在弱负相关。年NDVI和气温的正相关中心在中亚南部地区,负相关中心则出现在哈萨克斯坦的西部和北部地区;NDVI和降水的相关性中心刚好与气温相反。此外,在近30年间的每年6月至9月,中亚地区NDVI与气温存在近一个月的时间延迟现象。本研究为中亚干旱区生态系统变化和中亚地区碳循环的估算提供科学依据。     

Rattus colletti (Rodentia: Muridae) in the Australian wet-dry tropics: Seasonal habitat preferences,population dynamics and the effects of buffalo (Bubalus bubalis)

Population dynamics and habitat preferences of the dusky rat, Rattus colletti, were examined in the seasonal wetlands of the South Alligator River. Northern Territory, between late 1979 and 1982. Demographically, the species is characterized by short-term seasonal shifts between habitats superimposed on a longer-term irregular pattern of prolonged breeding and population irruption, followed by periods of relative rarity. These patterns are determined by the train of climatic events. The flexible life history strategy and movement patterns of R. colletti reflect fine-scale adaptation to a climatic regimen which is markedly seasonal, but also highly variable between years in the amount and temporal patterning of rainfall. The distribution of R. colletti amongst vegetation types is influenced by two sets of environmental factors, both reflecting a gradient in elevation, soil type and vegetation. The primary factors are vegetative cover and height, and the extent and duration of flooding; the secondary set comprises buffalo-induced features such as the degree of pugging and grazing. These factors are interrelated, and their relative importance to R. colletti varies greatly between seasons. Feral buffalo appear to exacerbate the harsh effects of the wet and dry seasons. The removal of these animals may ameliorate environmental conditions considerably, both temporally and spatially, resulting m generally higher, more stable and spatially less variable populations of R. colletti.     

Ecosystem properties of semiarid savanna grassland in West Africa and its relationship with environmental variability

The Dahra field site in Senegal, West Africa, was established in 2002 to monitor ecosystem properties of semiarid savanna grassland and their responses to climatic and environmental change. This article describes the environment and the ecosystem properties of the site using a unique set of in situ data. The studied variables include hydroclimatic variables, species composition, albedo, normalized difference vegetation index (NDVI), hyperspectral characteristics (350–1800 nm), surface reflectance anisotropy, brightness temperature, fraction of absorbed photosynthetic active radiation (FAPAR), biomass, vegetation water content, and land‐atmosphere exchanges of carbon (NEE) and energy. The Dahra field site experiences a typical Sahelian climate and is covered by coexisting trees (~3% canopy cover) and grass species, characterizing large parts of the Sahel. This makes the site suitable for investigating relationships between ecosystem properties and hydroclimatic variables for semiarid savanna ecosystems of the region. There were strong interannual, seasonal and diurnal dynamics in NEE, with high values of ~?7.5 g C m^?2 day^?1 during the peak of the growing season. We found neither browning nor greening NDVI trends from 2002 to 2012. Interannual variation in species composition was strongly related to rainfall distribution. NDVI and FAPAR were strongly related to species composition, especially for years dominated by the species Zornia glochidiata. This influence was not observed in interannual variation in biomass and vegetation productivity, thus challenging dryland productivity models based on remote sensing. Surface reflectance anisotropy (350–1800 nm) at the peak of the growing season varied strongly depending on wavelength and viewing angle thereby having implications for the design of remotely sensed spectral vegetation indices covering different wavelength regions. The presented time series of in situ data have great potential for dryland dynamics studies, global climate change related research and evaluation and parameterization of remote sensing products and dynamic vegetation models.     

基于ICEEMDAN方法的黄土高原植被覆盖变化及其对气候变化的响应

地理数据和遥感数据的长期序列中包含噪声和周期性波动信息。本研究基于ICEEMDAN方法对黄土高原1982—2015年归一化植被指数(NDVI)、降雨和温度进行逐像元分解,分解后得到的残差项减少了原始数据中的噪声和周期性波动,并利用残差项研究NDVI的变化趋势以及NDVI与气候因子之间的关系。结果表明: 1982—2015年,黄土高原NDVI以上升为主,残差项NDVI变化趋势的显著性(95.9%)大于原始NDVI变化趋势的显著性(72.3%),并且存在一定的空间差异性。温度和降雨的变化可以在很大程度上解释植被覆盖的变化。其中,温度与黄土高原NDVI之间呈极显著正相关的区域占83.7%,极显著负相关区域占13.9%;降雨与黄土高原NDVI之间呈极显著正相关的区域占54.4%,极显著负相关区域占37.2%。黄土高原植被对气候变化的响应存在明显的空间差异性,不同气候因子对不同植被覆盖类型的影响程度不同。总体上,黄土高原生长季不同植被与温度之间的相关性强于降水,温度是影响黄土高原植被覆盖变化的主要因素。     

Enrichment of land-cover polygons with eco-climatic information derived from MODIS NDVI imagery

Aim The FAO land‐cover classification system (LCCS) represents an innovative approach to standardizing and harmonizing land‐cover classifications based on remote sensing data. The thematic information considered by the LCCS, however, is intrinsically related to vegetation physiognomy and does not report important eco‐climatic features. Our aim is to develop a methodology to enrich LCCS maps with information on vegetation productivity and phenology derived from Moderate Resolution Imaging Spectroradiometer (MODIS) normalized difference vegetation index (NDVI) data. Location The LCCS has recently been applied in East Africa by the Africover project. The proposed methodology is developed and tested in Tanzania using MODIS NDVI data for a 5‐year period (2001–05). Methods Annual NDVI profiles of Africover polygons were extracted from MODIS imagery. These profiles, composed of 23 NDVI values per year, were averaged over the study period, purified for possible land‐cover errors and converted into a more manageable format composed of 24 half‐month values. The resulting NDVI profiles were first analysed visually and then evaluated statistically against rainfall measurements taken at 12 Tanzanian stations. The steps involved were as follows: NDVI values were aggregated on a monthly basis and represented with a one‐digit integer to obtain an extended code; a subset of parameters describing vegetation development and phenology was identified, thus obtaining a restricted codification; and finally, the information loss resulting from both the extended and restricted codification was evaluated with respect to the original NDVI profiles. Results NDVI profiles of different Africover classes can differ in mean values but tend to have a similar shape, linked to the seasonality of local vegetation. Both NDVI annual averages and seasonal variations are strictly dependent on rainfall patterns, particularly in arid zones. The tested codifications effectively summarize the eco‐climatic information contained in the polygon NDVI profiles, with the extended and restricted codifications retaining > 90% and 80% of such information, respectively. Main conclusions The proposed methodology is capable of enriching LCCS polygons with eco‐climatic information derived from MODIS NDVI data. Such information is related to vegetation development and seasonality, and can be efficiently condensed at various levels of detail.     

Patterns of macro and microhabitat use of two rodent species in relation to agricultural practices

Habitat selection may reflect the location of the home ranges or the allocation of shelter and foraging sites within a given habitat. We studied seasonal patterns of habitat use by Akodon azarae and Calomys laucha at two spatial scales: between maize fields and their weedy edges (macrohabitats), and associations of rodents captures with vegetation variables at the trap site level (microhabitats). We evaluated if the different habitat uses were related to disturbances generated by practices associated to maize cycle. A. azarae used mainly field edges, but it showed an increased use of maize fields when the crop reached maturity in summer. Contrarily, C. laucha used maize fields in a higher proportion than edges in all seasons. C. laucha was more influenced by microhabitat characteristics than A. azarae. C. laucha was present in sites with abundant dicot weeds when maize was growing up, while it was associated to sites with weeds with scarce cover in stubble maize fields. Before harvesting, both species were segregated at the microscale within maize fields. A. azarae was related to sites with high availability of green plant cover and C. laucha occupied low-quality sites, probably attributed to differences in their diets. We conclude that the pattern of habitat use by both species is best predicted at the macrohabitat scale, and when they are impoverished and present internal heterogeneity, there is selection at microhabitat scale of those better sites. While A. azarae responds to changes in vegetation cover and habitat structure associated to agricultural practices, C. laucha uses cropfields in an opportunistic way, affected by interspecific competition.     

The influence of climate variability on numbers of three waterbird species in Western Port, Victoria, 1973–2002

Seasonal and annual movements of Australian waterbirds are generally more complex than those of their Northern Hemisphere counterparts, and long-term data are needed to understand their relationships with climatic variables. This paper explores a long-term (1973–2002) set of waterbird counts from coastal Victoria and relates them to climatic data at local and continental scales. Three species (Black Swan Cygnus atratus, White-faced Heron Egretta novaehollandiae and Grey Teal Anas gracilis) were chosen for this analysis. Black Swans have large local breeding populations near the study region; White-faced Herons have smaller local breeding populations and Grey Teal breed extensively in ephemeral inland floodplains, such as those in the Murray-Darling Basin. All showed significant relationships with streamflow, regional rainfall and the Southern Oscillation Index (SOI) at appropriate scales and time-lags, with streamflow explaining the most variance. Black Swans showed a strong seasonal cycle in abundance and local climate variables had the greatest influence on the counts. Numbers were positively correlated with streamflow in southern Victoria three to six seasons before each count. Broader-scale climatic patterns were more important for the other two species. Numbers of White-faced Herons were positively correlated with streamflow or rainfall over various parts of Australia seven to nine seasons before each count. Numbers of Grey Teal showed weak seasonal cycles, and were negatively correlated with rainfall in Victoria or the Murray-Darling Basin in the seasons before or during each count, and positively with streamflow in the Murray-Darling Basin 15–18 months before each count.