Differences In Habitat Quality Research Articles

Plant species richness increase across crop field–dry grassland edges masks diverging patterns in generalists and specialists

ContextThere is an urgent need to stop the biodiversity loss in European agricultural landscapes. These landscapes, due to their fragmentation, include a lot of edges, many of them between habitats of different quality in terms of biodiversity. ObjectivesHere, we ask how plant species richness is distributed from the interior of protected semi-natural grassland into the interior of adjacent crop fields, and which species groups determine the observed patterns.MethodsAt grassland–crop field interfaces in two German landscapes, we sampled the vegetation along transects extending 32 m into both habitats. Based on theory, we fitted different models to visualize the species richness curve along transects and selected the best model via AIC. ResultsThe best fitting model for all species was monotone over the interface with a minimum in the field and a maximum in the grassland. This shape was driven by the generalists, showing the same pattern, while grassland specialists showed a sigmoid curve with an increase only in the grassland. Arable specialists had a peak at the field edge and decreased towards the grassland. Curves for Ellenberg indicator values for moisture, nutrients and light showed the same shape as the overall species curve, yet with an inverse pattern for light. ConclusionsThis is the first study revealing gradual responses of plant species richness at the grassland–crop field interface with a high spatial resolution. As these adjacent habitats influence each other far into their neighbourhood, attention should be given when conserving biodiversity in agricultural landscapes, particularly in case of often small and scattered protected areas.

Temporal and Spatial Changes of Habitat Quality and Their Potential Driving Factors in Southwest China

Climate change and human activities have considerably changed the spatial patterns and functional elements of regional habitats. Understanding spatiotemporal changes in habitat quality (HQ) and their potential driving factors is essential for maintaining ecosystem health and protecting biodiversity. To explore the effect of physical and human factors on HQ changes in Southwest China, we firstly analyzed the land-use change intensity (LCI). We then evaluated spatiotemporal changes in HQ based on the InVEST model and explored the spatial heterogeneity of the main driving factors of HQ changes based on a geographical detector and a geographical weighted regression model. The results showed that LCI had obvious spatiotemporal differences, and LCI from low-quality habitat to high-quality habitat (LCI1) was significantly higher than that from high-quality habitat to low-quality habitat (LCI2). The HQ improved steadily in Southwest China in 1990–2015, showing a trend of low–high–low from southeast to northwest. Moreover, there were twelve factors, including aboveground biomass, ecological land area ratio, population density, slope, etc., which had a significant impact on the spatial differences in HQ, and the effects of different factors on HQ had observable spatial heterogeneity. The effect of LCI2 on the spatial difference of HQ was greater than that of LCI1. These results suggested that the current ecosystem protection and management policy had a positive effect on improving HQ. Our study provides an important decision-making reference for sustainable land development and utilization and regional ecological protection and restoration.

Stressful living in lower-quality habitats? Body mass, feeding behavior and physiological stress levels in wild wood mouse populations.

Wild populations are continuously subjected to changes in environmental factors that pose different challenges. Body condition and hormones have been commonly used as health indicators due to their potential correlation with fitness. In the present study, we analyzed whether habitats of different quality influenced body mass, food intake and physiological stress levels in wild wood mice (Apodemus sylvaticus). Field work was seasonally carried out in Holm oak woods and pine forests in central Spain. A total of 93 wood mice from 4 different populations (2 per habitat type) were live-trapped. From each captured individual we noted body mass and food intake, measured as the amount of bait remaining in each trap. The physiological stress levels were measured non-invasively in collected fresh feces by quantifying fecal corticosterone metabolites (FCM) with a 5a-pregnane-3ß,11ß, 21-triol-20-one enzyme immunoassay. Wood mice abundances decreased from spring to summer, were higher in Holm oak woods than in pine forests and also resulted in different age-class distribution between both habitats. Individuals inhabiting pine forests showed a lower body mass and increased food intake, probably because of the comparatively lower food quality and availability in this habitat. Furthermore, these individuals showed increased physiological stress levels, likely due to the lower quality habitat in relation to both food and vegetation cover availability. Overall, besides affecting local wood mouse abundance, our study underscores the effect of habitat quality on body mass, food intake and the endocrine stress response. Considering the wood mouse's pivotal position in ecosystems, these results could help in the understanding of environmental traits hampering the viability of wild populations.

Spatio-temporal variation of strawberry aphid populations and their parasitoids

Aphids are common herbivores in the strawberry crop that can reduce plant vigor and fruit quality and also transmit viruses. Aphid species prefer diverse plant organs, which represent particular habitats of different quality for aphids and for the development of natural enemies’ populations. Different habitat units (young leaves, mature leaves, buds, flowers) of strawberry were sampled fortnightly during all seasons. We identified seven aphid species, namely Chaetosiphon fragaefolii, Aphis gossypii, and Macrosiphum euphorbiae, the most abundant. During the autumn, C. fragaefolli and M. euphorbiae were scarce and A. gossypii was denser on mature leaves, while during summer M. euphorbiae was absent. During the winter, C. fragaefolii predominated on buds and young leaves, A. gossypii on flowers, and both species on mature leaves. During the spring, C. fragaefolii was even more abundant on buds, A. gossypii predominated on mature leaves, and the three species were equally abundant on flowers and young leaves. Parasitoids emerged from A. gossypii, M. euphorbiae and Myzus persicae, but not from C. fragaefolii. Three Aphidius and two Aphelinus species were recovered. All primary parasitoid species emerged from A. gossypii, and secondary parasitoids emerged only from this aphid. Aphis gossypii parasitism on mature leaves was markedly higher in winter and summer than in autumn and spring. Parasitism of A. gossypii was independent of its density, and the number of parasitized aphids was never higher than six. Our results contribute to define the most appropriate sample unit to estimate aphid density of different species and provide information about seasonal natural parasitism.

Context-dependent effects of feather corticosterone on growth rate and fledging success of wild passerine nestlings in heterogeneous habitat.

Life history theory seeks answers to questions about how suites of traits, like growth rate, body mass and survival, have coevolved to maximize the fitness of individuals. In stochastic environments, individual fitness may be closely linked to environmental conditions experienced early in life. When conditions deteriorate, animals have to adapt physiologically to avoid detrimental effects to growth and survival. Hormones such as glucocorticoids are potentially important mediators of developmental plasticity, although their function is quite poorly understood in free-living animals to date. In this study, we used brood-size manipulation in wild great tits (Parus major) to see whether resource (e.g. food) availability can change feather corticosterone levels, somatic growth and fledging success in nestlings raised in habitats of different quality. Recent studies suggest that feather corticosterone offers a long-term hormonal measure for the main avian glucocorticoid by integrating the plasma levels of corticosterone over the whole nestling period. We showed that feather corticosterone, growth rate and fledging success were significantly affected by the treatment only in coniferous forests where growth conditions had a tendency to be poorer than in deciduous forests. We also found that feather corticosterone was negatively related to fledging success, and this effect was more pronounced in coniferous habitat. Our results suggest that feather corticosterone could offer an important physiological measure for nestling performance, mediated by a context-dependent developmental trade-off between immediate and future survival.

Gravel bars can be critical for biodiversity conservation: a case study on scaly-sided Merganser in South china.

Gravel bars are characteristic components of river landscapes and are increasingly recognized as key sites for many waterbirds, though detailed studies on the ecological function of gravel bars for waterbirds are rare. In this study, we surveyed the endangered Scaly-sided Merganser Mergus squamatus along a 40 km river section of Yuan River, in Central China, for three consecutive winters. We derived the landscape metrics of river gravel bars from geo-rectified fine resolution (0.6 m) aerial image data. We then built habitat suitability models (Generalized Linear Models—GLMs) to study the effects of landscape metrics and human disturbance on Scaly-sided Merganser presence probability. We found that 1) the Scaly-sided Merganser tended to congregate at river segments with more gravel patches; 2) the Scaly-sided Merganser preferred areas with larger and more contiguous gravel patches; and 3) the number of houses along the river bank (a proxy for anthropogenic disturbance) had significantly negative impacts on the occurrence of the Scaly-sided Merganser. Our results suggest that gravel bars are vital to the Scaly-sided Merganser as shelters from disturbance, as well as sites for feeding and roosting. Therefore, maintaining the exposure of gravel bars in regulated rivers during the low water period in winter might be the key for the conservation of the endangered species. These findings have important implications for understanding behavioral evolution and distribution of the species and for delineating between habitats of different quality for conservation and management.

Providing insights on habitat connectivity for male brown bears: A combination of habitat suitability and landscape graph-based models

The combined study of movement patterns and habitat selection, behaviors that are affected by landscape structure, is of critical importance for effective conservation of wildlife. In the same context, maintaining connectivity is a key component for facilitating movement and ensuring species persistence. The brown bear is a wide-ranging predator that moves across large areas, crossing various habitats of different quality. Here, we provide a methodological framework that allowed us to explore the relative importance of habitat quality upon movement patterns and connectivity. First, we developed habitat-suitability models by using telemetry data of eight male brown bears (12,893 radio-locations) collected in Greece. Next, we combined habitat-suitability maps with real movement data to develop graph models that represent movement networks as inter-connected patches of different quality. Network analyses revealed that movement networks demonstrate some well-studied properties regarding their structure and robustness (i.e. scale-free and small-world), providing insights on the contribution of patches of different quality to connectivity. Less suitable patches were found to play a critical role for facilitating brown bear's movement and landscape connectivity. Our findings raise the importance of considering the entire habitat of brown bear in conservation planning rather than isolated patches of high quality, as it might have been revealed by simple habitat-suitability models. Our results highlight the need of assessing the importance of the intervening matrix for facilitating connectivity and movement specifically in the case of large and highly mobile species that do not perceive landscape as strictly dichotomous.

Habitat discrimination by gravid Anopheles gambiae sensu lato--a push-pull system.

BackgroundThe non-random distribution of anopheline larvae in natural habitats suggests that gravid females discriminate between habitats of different quality. Whilst physical and chemical cues used by Culex and Aedes vector mosquitoes for selecting an oviposition site have been extensively studied, those for Anopheles remain poorly explored. Here the habitat selection by Anopheles gambiae sensu lato (s.l.), the principal African malaria vector, was investigated when presented with a choice of two infusions made from rabbit food pellets, or soil.MethodsNatural colonization and larval survival was evaluated in artificial ponds filled randomly with either infusion. Dual-choice, egg-count bioassays evaluated the responses of caged gravid females to (1) two- to six-day old infusions versus lake water; (2) autoclaved versus non-autoclaved soil infusions; and assessed (3) the olfactory memory of gravid females conditioned in pellet infusion as larvae.ResultsWild Anopheles exclusively colonized ponds with soil infusion and avoided those with pellet infusion. When the individual infusions were tested in comparison with lake water, caged An. gambiae sensu stricto (s.s.) showed a dose response: females increasingly avoided the pellet infusion with increasing infusion age (six-day versus lake water: odds ratio (OR) 0.22; 95% confidence interval (CI) 0.1-0.5) and showed increasing preference to lay eggs as soil infusion age increased (six-day versus lake water: OR 2.1; 95% CI 1.4-3.3). Larvae survived in soil infusions equally well as in lake water but died in pellet infusions. Anopheles gambiae s.s. preferred to lay eggs in the non-autoclaved soil (OR 2.6; 95% CI 1.8-3.7) compared with autoclaved soil. There was no change in the avoidance of pellet infusion by individuals reared in the infusion compared with those reared in lake water.ConclusionWild and caged An. gambiae s.l. females discriminate between potential aquatic habitats for oviposition. These choices benefit the survival of the offspring. Although the study was not designed to distinguish between stimuli that acted over a distance or on contact, it could be demonstrated that the choice of habitat is mediated by chemical cues based on both preference and avoidance. These cues, if identified, might be developed for ‘push-pull’ strategies to improve malaria vector monitoring and control.

Predictive modelling to aid the regional-scale management of a vertebrate pest

Extensive resources are allocated to managing vertebrate pests, yet spatial understanding of pest threats, and how they respond to management, is limited at the regional scale where much decision-making is undertaken. We provide regional-scale spatial models and management guidance for European rabbits (Oryctolagus cuniculus) in a 260,791 km2 region in Australia by determining habitat suitability, habitat susceptibility and the effects of the primary rabbit management options (barrier fence, shooting and baiting and warren ripping) or changing predation or disease control levels. A participatory modelling approach was used to develop a Bayesian network which captured the main drivers of suitability and spread, which in turn was linked spatially to develop high resolution risk maps. Policy-makers, rabbit managers and technical experts were responsible for defining the questions the model needed to address, and for subsequently developing and parameterising the model. Habitat suitability was determined by conditions required for warren-building and by above-ground requirements, such as food and harbour, and habitat susceptibility by the distance from current distributions, habitat suitability, and the costs of traversing habitats of different quality. At least one-third of the region had a high probability of being highly suitable (support high rabbit densities), with the model supported by validation. Habitat susceptibility was largely restricted by the current known rabbit distribution. Warren ripping was the most effective control option as warrens were considered essential for rabbit persistence. The anticipated increase in disease resistance was predicted to increase the probability of moderately suitable habitat becoming highly suitable, but not increase the at-risk area. We demonstrate that it is possible to build spatial models to guide regional-level management of vertebrate pests which use the best available knowledge and capture fine spatial-scale processes.

Impact of host nutritional status on infection dynamics and parasite virulence in a bird‐malaria system

Host resources can drive the optimal parasite exploitation strategy by offering a good or a poor environment to pathogens. Hosts living in resource-rich habitats might offer a favourable environment to developing parasites because they provide a wealth of resources. However, hosts living in resource-rich habitats might afford a higher investment into costly immune defences providing an effective barrier against infection. Understanding how parasites can adapt to hosts living in habitats of different quality is a major challenge in the light of the current human-driven environmental changes. We studied the role of nutritional resources as a source of phenotypic variation in host exploitation by the avian malaria parasite Plasmodium relictum. We investigated how the nutritional status of birds altered parasite within-host dynamics and virulence, and how the interaction between past and current environments experienced by the parasite accounts for the variation in the infection dynamics. Experimentally infected canaries were allocated to control or supplemented diets. Plasmodium parasites experiencing the two different environments were subsequently transmitted in a full-factorial design to new hosts reared under similar control or supplemented diets. Food supplementation was effective since supplemented hosts gained body mass during a 15-day period that preceded the infection. Host nutrition had strong effects on infection dynamics and parasite virulence. Overall, parasites were more successful in control nonsupplemented birds, reaching larger population sizes and producing more sexual (transmissible) stages. However, supplemented hosts paid a higher cost of infection, and when keeping parasitaemia constant, they had lower haematocrit than control hosts. Parasites grown on control hosts were better able to exploit the subsequent hosts since they reached higher parasitaemia than parasites originating from supplemented hosts. They were also more virulent since they induced higher mass and haematocrit loss. Our study highlights that parasite virulence can be shaped by the host nutritional status and that parasite can adapt to the environment provided by their hosts, possibly through genetic selection.

Density‐dependent mortality in adults, but not juveniles, of stream‐resident brown trout (Salmo trutta)

Summary1. This study investigates when and where density dependence operates on the mortality rates of stream‐resident brown trout Salmo trutta. To this aim, I explored populations in habitats of different quality containing high, low or intermediate densities over broad scales of space and time. The study is based on census data of 170 cohorts quantified from recruitment to the total disappearance at 12 sites in four contrasting tributaries of the Rio Esva drainage (north‐western Spain), over the years 1986–2007.2. Log10‐transformed survivor density over time highlighted a consistent pattern for the 170 cohorts characterised by the occurrence of only two life stages. An early stage starts at recruitment, lasts about half the lifetime and shows no or negligible mortality. A threshold time at 425–620 days after emergence preceded a second stage of continuous and constant mortality until the final disappearance of the cohorts. Consequently, in all scenarios, mortality only occurred in the adult component and no effect of season, year, age‐class and/or reproductive stage was detected.3. Substantial spatial and temporal variations typified both recruitment (range R = 0.01–1.62 ind m−2) and adults’ mortality rates (range Z = 0.03–0.38 day−1). Nested anovas revealed strong effects of site and year on both recruitment and mortality with sites interspersed along the stream gradients where recruitment and mortality were typically high relative to other sites located either nearby in the same stream or distant in another stream, where both recruitment and mortality rates were typically low or intermediate.4. Adult mortality rates plotted against recruitment for the 170 cohorts pooled revealed a continuous, positive power relationship that explained 45.3% of variation in mortality rates over the whole range of recruitment values. Similarly, highly significant power relationships were elucidated for site‐specific mortality rates averaged across years and for annual‐specific mortality rates averaged across sites against the corresponding mean recruitment averaged across years and sites, respectively. These relationships support the hypothesis that the operation of density dependence is scale independent and context independent but operates in a continuous manner across all scenarios examined.5. A chronic effect of density dependence on adult losses induces temporally persistent populations maintained by a low number of spawners. Apparently, the operation of density dependence adjusts the number of spawners to the availability of rearing and spawning habitat. This dynamic process may also help to explain the small effective population size (Ne) recently documented by genetic studies of stream‐living brown trout and other salmonids.

Towards a more exact definition of the importance of competition - a reply to Freckleton et al. (2009)

Summary 1. Freckleton, Watkinson & Rees (2009) criticize a recent paper by ourselves in this journal (Brooker & Kikvidze 2008) as well as our earlier work on competition importance (Brooker et al. 2005). In response, here we clarify our ideas with the aim of defining more clearly the key points of scientific debate, specifically (i) the definition of the importance of competition and (ii) its measurement. 2. Freckleton, Watkinson & Rees (2009) interpret the classic paper by Welden & Slauson (1986) such that importance as a concept relates to long-term, population-level consequences of competition. However, we consider competition importance to be the proportional impact of competition relative to the overall impact of the environment, and our index Cimp expresses changes in competition importance – as defined by ourselves – along productivity gradients. We argue that our definition more accurately reflects the work of Welden & Slauson, as well as a more recent use of the concept (Grace 1991), which precedes the work of Freckleton & Watkinson (2001). 3. We highlight that Cimp was never proposed as a general index of competition importance, but is readily applicable in certain circumstances. Notably, our index and the approaches to measuring competition importance as set out by Freckleton, Watkinson & Rees (2009) are not unrelated. 4. We also discuss some recent additional responses to both our (2008) paper and that by Freckleton, Watkinson & Rees (2009), including applications of the concept of competition importance. Although the authors of these papers may not have used our index Cimp, they follow the same definitions for the overall concept of competition importance as ourselves. 5. Synthesis. We conclude that the complex topic of biotic interactions, including the specific issue of the importance of competition, invites a range of approaches. Importantly, these approaches can be complementary and not conflicting. Here, we propose what we see as a sensible resolution to the current debate concerning the definition of competition importance, a resolution which is backed by the original source article, literature precedent and current usage.

Exploring habitat use by cheetahs using ecological niche factor analysis

AbstractUnderstanding the basis of habitat choice having important implications for explaining the distribution of organisms, as well as helping to differentiate between habitats of different quality for effective management. In this study, the effects of sex, age and reproductive status on habitat use patterns of cheetahs Acinonyx jubatus in the Serengeti plains were explored using Ecological Niche Factor Analysis (ENFA). Our results showed that gender and territoriality did not affect patterns of habitat use. However, females tended to be more specialized when they were young than when they were older, displaying a more restricted ecological niche. Likewise, older females without cubs were more specialized than the same adult females with young cubs. This result did not hold for younger females. Altogether, the ENFA approach allowed us to (1) use the large amount of incidental sighting data collected over 12 years on cheetah spatial distribution; (2) identify the importance of reproductive status and age on the relationship between animals and their habitat; (3) further demonstrate that ENFA is applicable in a wide range of situations, including for exploring individual variation in niche definition.

Habitat fragmentation and adaptation: a reciprocal replant–transplant experiment among 15 populations ofLychnis flos‐cuculi

SummaryHabitat fragmentation and variation in habitat quality can both affect plant performance, but their effects have rarely been studied in combination. We thus examined plant performance in response to differences in habitat quality for a species subject to habitat fragmentation, the common but declining perennial herbLychnis flos‐cuculi.We reciprocally transplanted plants between 15 fen grasslands in north‐east Switzerland and recorded plant performance for 4 years.Variation between the 15 target sites was the most important factor and affected all measures of plant performance in all years. This demonstrates the importance of plastic responses to habitat quality for plant performance.Plants from smaller populations produced fewer rosettes than plants from larger populations in the first year of the replant–transplant experiment.Plant performance decreased with increasing ecological difference between grassland of origin and target grassland, indicating adaptation to ecological conditions. In contrast, plant performance was not influenced by microsatellite distance and hardly by geographic distance between grassland of origin and target grassland.Plants originating from larger populations were better able to cope with larger ecological differences between transplantation site and site of origin.Synthesis: In addition to the direct effects of target grasslands, both habitat fragmentation, through reduced population size, and adaptation to habitats of different quality, contributed to the performance ofL. flos‐cuculi. This underlines that habitat fragmentation also affects species that are still common. Moreover, it suggests that restoration projects involvingL. flos‐cuculishould use plant material from large populations living in habitats similar to the restoration site. Finally, our results bring into question whether plants in small habitat remnants will be able to cope with future environmental change.

Feeding behaviour of birds foraging on predictable resources in habitats of different quality

Using the density of food left in a patch after foraging — i.e. the giving-up density (GUD) — as a behavioural indicator, short-term foraging studies on birds in the dry and wet fringing forests and savanna habitats of the Amurum Forest Reserve, Laminga, Nigeria, were used to evaluate whether widespread food abundance will affect their behaviour in these apparently-different habitats. The effect of the dry season on feeding activity and the effects of temperature within, and between, days were also investigated. Results showed that GUDs were highest in dry fringing forests, intermediate in wet fringing forests, and lowest in savanna. This difference may have been as a result of a difference in food abundance between habitats. The availability of water in the wet fringing forests may have affected the feeding behaviour of the birds in the wet gully habitat compared with those of the dry gully. The behaviour of birds in response to time of day was affected by temperature, as there was no difference between GUDs in open and covered habitats in the mornings at lower temperatures, but lower GUDs were recorded in cover (at higher temperatures) in the afternoon when birds may — due to thermoregulatory costs — retreat to cover more often. However, temperature had no effect on GUDs over season. A reduction in GUDs towards the end of the dry season, as food resources deplete, gives further credence to the observation that food abundance affects behaviour.

Efficacy of PIT tags and an autonomous antenna system to study the juvenile life stage of an estuarine-dependent fish

Many marine fishes use spatially distinct habitats as juveniles and adults. Determining which juvenile habitats are most important to sustaining adult populations (i.e., which habitats are nurseries) has proven difficult, in part due to challenges in estimating survival of juveniles in putative nursery habitats. Recent technological advances have made large- scale tagging efforts a viable approach to estimating survival of juvenile fishes by increasing recapture rates and enabling the use of individual-identification tags. These techniques, using Passive Integrated Transponder (PIT) tags and autonomous antenna detection systems (antenna), have been successfully applied in freshwater environments. This paper reports the adaptation of these techniques to estuarine mangrove creeks (salinity: 2-28%) for research of the juvenile life stage on an estuarine-dependent marine fish, Centropomus undecimalis. Retention rate of PIT tags in juveniles .120 mm standard length was 100%, with no mortality. The antenna detection field covered 48% of the creek water column, and the antenna was experimentally determined to detect approximately 67% of tagged fish that swam through. Overall recapture rate of tagged fish by the antenna was .40%. This recapture rate is higher than the sparse data typical of traditional tag-recapture studies. A time-dependent Jolly-Seber model was fit to the data, providing estimates of capture probability (0.8) and weekly apparent survival (0.41) that will be invaluable in comparing juvenile habitats of different quality (e.g., natural versus anthropogenically degraded). This research demonstrates the viability of this approach to fish research in estuarine habitats.

A Thirty-Year Study of Phenotypic and Genetic Variation of Blue Tits in Mediterranean Habitat Mosaics

Abstract In recent years, the study of phenotypic and genetic variation has been enhanced by combining genetic, physiological, demographic, and behavioral components of life histories. Using these new approaches, we address the problem of adaptation to environmental heterogeneity by examining in detail the variation of several fitness-related traits in a small passerine bird, the blue tit, which has been extensively studied in habitat mosaics of the Mediterranean region. The response of blue tits to spatial habitat heterogeneity depends on their range of dispersal relative to the size of habitat patches. Dispersal over short distances leads to local specialization, whereas dispersal over long distances leads to phenotypic plasticity. Gene flow between habitats of different quality may produce local maladaptation and a source–sink population structure. However, when habitat-specific divergent selection regimes are strong enough to oppose the effects of gene flow, local adaptation may arise on a scale that ...

Resource Availability Controls Bird-Assemblage Composition Through Interspecific Aggression

AbstractHigh-value resources are often defended aggressively by consumers, which can alter assemblage structure and dynamics. Here, we describe a system of nectarivorous bird assemblages exploiting pockets of eucalypt woodlands that differ dramatically in flowering and provision of nectar. The behavioral dominant, the Red Wattlebird (Anthochaera curunculata), aggressively reduces the occurrence and activities of other honeyeaters of the genera Lichenostomus and Melithreptus on sites of intense flowering. The latter genera predominate in moderately flowering areas, but few honeyeaters occupy poorly flowering sites. To understand such systems, in which temporal variation in habitat quality can be great, one needs to consider not only the disparity in habitat quality among locations but also the spatial extent of habitats of different quality. Isoleg analysis is a theoretical tool developed to understand how dominant and subordinate species partition habitats as a function of their respective densities. Our results suggest that isoleg analysis needs to be developed with spatial explicitness to capture variation in extent of habitats of different qualities and consequent effects on the usefulness of aggression for domination of resources.La Disponibilidad de Recursos Controla la Composición de los Ensambles de Aves a través de las Agresiones Interespecíficas

RESOURCE AVAILABILITY CONTROLS BIRD-ASSEMBLAGE COMPOSITION THROUGH INTERSPECIFIC AGGRESSION

Abstract High-value resources are often defended aggressively by consumers, which can alter assemblage structure and dynamics. Here, we describe a system of nectarivorous bird assemblages exploiting pockets of eucalypt woodlands that differ dramatically in flowering and provision of nectar. The behavioral dominant, the Red Wattlebird (Anthochaera curunculata), aggressively reduces the occurrence and activities of other honeyeaters of the genera Lichenostomus and Melithreptus on sites of intense flowering. The latter genera predominate in moderately flowering areas, but few honeyeaters occupy poorly flowering sites. To understand such systems, in which temporal variation in habitat quality can be great, one needs to consider not only the disparity in habitat quality among locations but also the spatial extent of habitats of different quality. Isoleg analysis is a theoretical tool developed to understand how dominant and subordinate species partition habitats as a function of their respective densities. Our...

Consequences of the settlement of migrant European Robins Erithacus rubecula in wintering habitats occupied by conspecific residents

In wintering areas where migrant birds meet sedentary conspecifics, early settlement of local residents in the best habitat patches might reduce the availability of suitable sites for arriving migrants. We studied how sympatric migratory and sedentary European Robins Erithacus rubecula occupy two wintering habitats of different quality (forests and shrublands) in southern Spain, and how such a distribution affects individuals of each population sector. In September, before migrants arrived, Robins were only found in forests, and they had already saturated these habitats, so that rather than increasing Robin abundance in these habitats, the arrival of migrants caused a massive occupation of the previously vacant shrublands. During the winter, we captured Robins and identified them as migrants or residents using a discriminant function based on morphological traits. Residents always predominated in forests, and migrants in shrublands, but through the winter around 35% of residents (mainly juveniles) moved to shrublands, having been replaced by some migrants in forests. Although food was more abundant in shrublands, Robins had better body condition in forests, suggesting that other factors determined habitat preferences (e.g. shelter availability or food diversity, which were higher in forests). In addition, we observed a greater variance in body mass relative to body size in forests, suggesting that energy management was less constrained in this habitat (for example owing to a lower exposure to predators or a higher food predictability). Our results suggest that sedentary Robins benefit from an early occupation of the best habitats in the wintering grounds, forcing migrants to colonize apparently less suitable sites. This would explain the persistence of these small southern populations despite the yearly flooding of the area by huge numbers of migrant conspecifics.