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Resident Species (resident + species)
Selected AbstractsWhere do Swainson's hawks winter?DIVERSITY AND DISTRIBUTIONS, Issue 5 2008Satellite images used to identify potential habitat ABSTRACT During recent years, predictive modelling techniques have been increasingly used to identify regional patterns of species spatial occurrence, to explore species,habitat relationships and to aid in biodiversity conservation. In the case of birds, predictive modelling has been mainly applied to the study of species with little variable interannual patterns of spatial occurrence (e.g. year-round resident species or migratory species in their breeding grounds showing territorial behaviour). We used predictive models to analyse the factors that determine broad-scale patterns of occurrence and abundance of wintering Swainson's hawks (Buteo swainsoni). This species has been the focus of field monitoring in its wintering ground in Argentina due to massive pesticide poisoning of thousands of individuals during the 1990s, but its unpredictable pattern of spatial distribution and the uncertainty about the current wintering area occupied by hawks led to discontinuing such field monitoring. Data on the presence and abundance of hawks were recorded in 30 × 30 km squares (n = 115) surveyed during three austral summers (2001,03). Sixteen land-use/land-cover, topography, and Normalized Difference Vegetation Index (NDVI) variables were used as predictors to build generalized additive models (GAMs). Both occurrence and abundance models showed a good predictive ability. Land use, altitude, and NDVI during spring previous to the arrival of hawks to wintering areas were good predictors of the distribution of Swainson's hawks in the Argentine pampas, but only land use and NDVI were entered into the model of abundance of the species in the region. The predictive cartography developed from the models allowed us to identify the current wintering area of Swainson's hawks in the Argentine pampas. The highest occurrence probability and relative abundances for the species were predicted for a broad area of south-eastern pampas that has been overlooked so far and where neither field research nor conservation efforts aiming to prevent massive mortalities has been established. [source] Refuge-mediated apparent competition in plant,consumer interactionsECOLOGY LETTERS, Issue 1 2010John L. Orrock Abstract At the intersection of consumer behaviour and plant competition is the concept of refuge-mediated apparent competition: an indirect interaction whereby plants provide a refuge for a shared consumer, subsequently increasing consumer pressure on another plant species. Here, we use a simple model and empirical examples to develop and illustrate the concept of refuge-mediated apparent competition. We find that the likelihood that an inferior competitor will succeed via refuge-mediated apparent competition is greater when competitors have similar resource requirements and when consumers exhibit a strong response to the refuge and high attack rates on the superior competitor. Refuge-mediated apparent competition may create an emergent Allee effect, such that a species invades only if it is sufficiently abundant to alter consumer impact on resident species. This indirect interaction may help explain unresolved patterns observed in biological invasion, such as the different physical structure of invasive exotic plants, the lag phase, and the failure of restoration efforts. Given the ubiquity of refuge-seeking behaviour by consumers and the ability of consumers to alter the outcome of direct competition among plants, refuge-mediated apparent competition may be an underappreciated mechanism affecting the composition and diversity of plant communities. Ecology Letters (2010) 13: 11,20 [source] Ecology of invasive mosquitoes: effects on resident species and on human healthECOLOGY LETTERS, Issue 5 2005Steven A. Juliano Abstract Investigations of biological invasions focus on patterns and processes that are related to introduction, establishment, spread and impacts of introduced species. This review focuses on the ecological interactions operating during invasions by the most prominent group of insect vectors of disease, mosquitoes. First, we review characteristics of non-native mosquito species that have established viable populations, and those invasive species that have spread widely and had major impacts, testing whether biotic characteristics are associated with the transition from established non-native to invasive. Second, we review the roles of interspecific competition, apparent competition, predation, intraguild predation and climatic limitation as causes of impacts on residents or as barriers to invasion. We concentrate on the best-studied invasive mosquito, Aedes albopictus, evaluating the application of basic ecological theory to invasions by Aedes albopictus. We develop a model based on observations of Aedes albopictus for effects of resource competition and predation as barriers to invasion, evaluating which community and ecosystem characteristics favour invasion. Third, we evaluate the ways in which invasive mosquitoes have contributed to outbreaks of human and animal disease, considering specifically whether invasive mosquitoes create novel health threats, or modify disease transmission for existing pathogen,host systems. [source] A meta-analysis of biotic resistance to exotic plant invasionsECOLOGY LETTERS, Issue 10 2004Jonathan M. Levine Abstract Biotic resistance describes the ability of resident species in a community to reduce the success of exotic invasions. Although resistance is a well-accepted phenomenon, less clear are the processes that contribute most to it, and whether those processes are strong enough to completely repel invaders. Current perceptions of strong, competition-driven biotic resistance stem from classic ecological theory, Elton's formulation of ecological resistance, and the general acceptance of the enemies-release hypothesis. We conducted a meta-analysis of the plant invasions literature to quantify the contribution of resident competitors, diversity, herbivores and soil fungal communities to biotic resistance. Results indicated large negative effects of all factors except fungal communities on invader establishment and performance. Contrary to predictions derived from the natural enemies hypothesis, resident herbivores reduced invasion success as effectively as resident competitors. Although biotic resistance significantly reduced the establishment of individual invaders, we found little evidence that species interactions completely repelled invasions. We conclude that ecological interactions rarely enable communities to resist invasion, but instead constrain the abundance of invasive species once they have successfully established. [source] Use of Caged Nucella Lapillus and Crassostrea Gigas to Monitor Tributyltin-Induced Bioeffects in Irish Coastal Waters,ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 8 2009Michelle Giltrap Abstract Caging studies have been previously reported to be useful for providing valuable information on biological effects of mollusks over short periods of time where resident species are absent. The degree of imposex in caged dog whelk (Nucella lapillus), was measured using the vas deferens sequence index (VSDI) and the Relative Penis Size Index (RPSI) and the extent of shell thickening in caged Pacific oyster (Crassostrea gigas) was investigated at t = 0 and t = 18 weeks. Nucella lapillus, when provided with mussels as a food source at the control site at Omey Island on the west Irish coast, did not demonstrate imposex features, whereas those transplanted to port areas did. Dunmore East exhibited the highest level of imposex (3.25 VDSI and 2.37 RPSI). Shell thickening was evident in C. gigas transplanted to Dunmore East, with low effects evident at the control location, Omey Island, and Dublin Bay at t = 18 weeks. Dry weight whole-body concentrations of organotins were most elevated in all species held at Dunmore East compared with other locations. Greatest ,15N and ,13C enrichment was observed within the tissues of the predatory N. lapillus in all three test sites. Increased assimilation in the Dublin Bay oysters might have been influenced by the presence of more nutrients at this location. Surficial sediment organotin levels were most elevated in the Dunmore East <2-mm fraction (22,707 ,g tributyltin/kg dry weight), whereas low organotin levels were determined from Dublin and Omey Island sediments. The valuable application of cost-effective caging techniques to deliver integrated biological effects and chemical measurements in the absence of resident gastropod populations in potential organotin/tributyltin hotspot locations is discussed. [source] The concept of the taxon cycle in biogeographyGLOBAL ECOLOGY, Issue 5 2002Robert E. Ricklefs Abstract Taxon cycles are sequential phases of expansion and contraction of the ranges of species, associated generally with shifts in ecological distribution. The important contribution of the taxon cycle to biogeographical analysis is its emphasis on evolutionary and ecological interactions among colonizing and resident species, which influence their extinction dynamics and establish patterns of geographical distribution. Taxon cycles were inferred originally from the distribution of species across island archipelagos, where a correlation was noted between gaps in island occupancy and the degree of phenotypic differentiation. This pattern implied that phases of colonization were followed by range contraction, while endemic Antillean species that were undifferentiated between islands suggested secondary expansion and the beginning of a new cycle. This interpretation was met with scepticism, but reconstruction of phylogenetic relationships from gene sequences has now permitted us to characterize taxon cycles in Lesser Antillean birds. The relative timing of phases of the cycle can be deduced from genetic divergence between island populations. We have found that taxon cycles have periods in the order of 106 years and that cycles in different lineages occur independently of each other and independently of Pleistocene climate cycles. Individual island populations may persist for several millions of years on the larger islands of the Lesser Antilles; occasional expansion phases lead to the replacement of island populations that have disappeared, thus reducing the archipelago-wide rate of extinction to nil. What drives taxon cycles is unknown, but we speculate that they may be caused by co-evolution with enemy populations, and a probable mechanism would involve infrequent mutations influencing parasite virulence and avian host disease resistance. Taxon cycles undoubtedly occur on continents, but the geographical configuration of island archipelagos reveals more clearly their presence and invites their study. [source] Plant invasions and the nicheJOURNAL OF ECOLOGY, Issue 4 2009Andrew S. MacDougall Summary 1For plant invaders, being different is often equated with being successful, yet the mechanistic connection remains unclear. 2Classic niche theory predicts that invaders with niches distinct from the native flora should coexist with little interaction with native species, yet such invaders often have substantial impacts. Meanwhile, invaders that overlap in niche space with native species should either be repelled or dominate, yet these invaders often naturalize with little effect. Such discrepancies between theory and observation raise questions about how species differences influence invader establishment and impact. 3Here, we review these issues in light of recent work on coexistence theory, which shows how niche and fitness differences between natives and invaders interact to determine invasion outcomes. We show how successful invader establishment depends on either a fitness advantage or niche difference from resident species, but that only the former allows invaders to become dominant. 4By identifying the role of niche and fitness differences in leading invasion hypotheses, we unify their predictions for invasion success while highlighting new approaches for evaluating the importance of species differences for invasion. 5Synthesis. Situating the invasion process within a recent coexistence framework broadens our understanding of invasion mechanisms and more tightly links problems in invasion ecology with our more general understanding of community dynamics. [source] Invasion impacts diversity through altered community dynamicsJOURNAL OF ECOLOGY, Issue 6 2005KATHRYN A. YURKONIS Summary 1Invading plant species often alter community structure, composition and, in some instances, reduce local diversity. However, the community dynamics underlying these impacts are relatively unknown. 2Declines in species richness with invasion may occur via displacement of resident species and/or reduction of seedling establishment by the invader. These two mechanisms differ in the demographic stage of the interaction. 3We document turnover dynamics using long-term permanent plot data to assess the mechanism(s) of invasion impacts of four exotic species on a mixed community of native and exotic species. These mechanisms were evaluated at both the neighbourhood (1-m2 plot) and population (individual species) scales. 4During invasion, species richness declined with increasing invader cover for three of the four invaders. All invaders reduced colonization rates, but had no effect on extinction rates at the neighbourhood scale. Populations differed in their susceptibility to invasion impacts, with significant reductions in colonization for 10 of 25 (40%) species and increases in extinction for only 4 of 29 (14%) species. 5At neighbourhood and population scales, influences of invasion on community dynamics were essentially the same for all invaders regardless of life-form. While individual resident species had some increase in extinction probability, community richness impacts were largely driven by colonization limitation. 6The consistency of invasion impacts across life-forms suggests establishment limitation as a general mechanism of invasion impact. This common causal mechanism should be explored in other systems to determine the extent of its generality. [source] Competitive displacement or biotic resistance?JOURNAL OF VEGETATION SCIENCE, Issue 2 2010Disentangling relationships between community diversity, invasion success of tall herbs, shrubs Abstract Questions: Are negative invasion,diversity relationships due to biotic resistance of the invaded plant community or to post-invasion displacement of less competitive species? Do invasion,diversity relationships change with habitat type or resident traits? Location/species: Lowlands and uplands of western and southern Germany, Heracleum mantegazzianum; mountain range in central Germany, Lupinus polyphyllus; and coastal dunes of northwest Germany, Rosa rugosa. Methods: We tested the significance and estimated regression slopes of invasion,diversity relationships using generalized linear (mixed effects) models relating invader cover and habitat type to species richness in different plant groups, stratified based on size, life cycle and community association. Results: We found negative, positive and neutral relationships between invader cover and species richness. There were negative linear correlations of invader cover with small plant species throughout, but no negative linear correlation with tall species. Invasion,diversity relationships tended to be more negative in early-successional habitats, such as dunes or abandoned grasslands, than in late-successional habitats. Conclusions: Invasion diversity,relationships are complex; they vary among habitat types and among different groups of resident species. Negative invasion,diversity relationships are due to asymmetric competitive displacement of inferior species and not due to biotic resistance. Small species are displaced in early-successional habitats, while there is little effect on persistence of tall species. [source] The importance of biological inertia in plant community resistance to invasionJOURNAL OF VEGETATION SCIENCE, Issue 3 2003Betsy Von Holle Abstract. Insights into the ecology of historic invasions by introduced species can be gained by studying long-term patterns of invasions by native species. In this paper, we review literature in palaeo-ecology, forest-stand simulation modelling, and historical studies of plant species invasions to illustrate the relevance of biological inertia in plant communities to invasion ecology. Resistance to invasion occurs in part because of environmental, demographic, and biotic factors influencing the arrival and establishment of invading species. We propose that biological inertia within the resident community is a fourth component of resistance to invasion, because of the lag time inherent in eliminating resident species and perhaps their traces after environmental conditions become suitable for invasion by immigrating species. Whether or not an introduced species invades can be conditioned by the presence of the pre-existing community (and/or its legacy) in addition to the other biotic and abiotic factors. [source] Energy density patterns of nectar resources permit coexistence within a guild of Neotropical flower-visiting batsJOURNAL OF ZOOLOGY, Issue 1 2004Marco Tschapka Abstract Neotropical rainforests support guilds of nectar feeding bats (Phyllostomidae: Glossophaginae) with up to six coexisting species. To analyse guild structure and mechanisms of coexistence in a Costa Rican tropical lowland rainforest, the resource use and morphology of bats were compared to the energetic characteristics of preferred nectar resources and their spatio-temporal distribution. The relative abundance of nectar-feeding bats was determined from mistnet captures over 26 months. Food items were identified by analysis of pollen loads and faecal samples. Phenology, flower density and nectar sugar content of resource plants permitted quantitative estimations of resource availability expressed as energy density (kJ ha,1 day,1) throughout the annual cycle. Four glossophagine bat species co-occurred at La Selva: two permanent residents (Glossophaga commissarisi, Hylonycteris underwoodi) and two seasonal species (Lichonycteris obscura, Lonchophylla robusta) that were found in small numbers during a period of high nectar availability. The two resident species differed in their abundance and in their temporal feeding strategies. After the main flowering peak, the common G. commissarisi shifted to a more frugivorous diet, while the rarer H. underwoodi fed on the few remaining bat-flowers. Resource plant species differed in their energy density by up to two orders of magnitude. Hylonycteris underwoodi visited more often plant species with a low energy yield than G. commissarisi. Because of its smaller body size and a wing morphology that promotes fast flight, H. underwoodi appears to be better adapted to low and scattered nectar resource levels. The two seasonal species differed greatly in body mass, which suggests different strategies for high-quality resource tracking. Large body mass in Lonchophylla robusta provides an energy buffer that permits daily commuting flights between a permanent roost and profitable foraging areas, while the small Lichonycteris obscura seems to track resources nomadically. It is proposed that energy density may be a major niche dimension that restricts access of species to certain habitats and that may profoundly influence the structure of nectar-feeding bat guilds. [source] Temporal distribution and composition of the ichthyoplankton from Leopoldo's Inlet on the Upper Paraná River floodplain (Brazil)JOURNAL OF ZOOLOGY, Issue 4 2002Reinaldo José de Castro Abstract Temporal distribution and composition of ichthyoplankton and their relationships with some environmental variables of Leopoldo's Inlet (Ressaco do Leopoldo) on the upper Paraná River floodplain, southern Brazil, were analysed. Samples were taken from February 1991 to February 1992, and 3480 larvae were collected. The highest density of larvae was observed in November 1991 (36.79 larvae/10 m3) at night (night/day ratio 7: 1). Species composition showed a predominance of Characiformes (80%). There was a high density (4.28 larvae/10 m3) of Bryconamericus stramineus throughout almost the whole study period. The majority of the species were more frequently collected at night. Pearson's correlation indicated a relationship between larval density, temperature, and pluviometric index. Leopoldo's Inlet, whose ichthyofauna is mainly composed of grazing and resident species, shows favourable conditions for fish reproduction and development. [source] When does ecosystem engineering cause invasion and species replacement?OIKOS, Issue 8 2008Andrew Gonzalez Introduced exotic species can dominate communities and replace native species that should be better adapted to their local environment, a paradox that is usually explained by the absence of natural enemies and by habitat alteration resulting from anthropogenic disturbance. Additionally, introduced species can enhance their invasion success and impact on native species by modifying selection pressures in their new environment through ecosystem engineering. We analyse a simple dynamic model of indirect competition for habitat between a non-engineering resident species and an engineering exotic species. The conditions for invasion and competitive exclusion of the resident by the exotic species and the range of dynamic outcomes suggested by the model are determined by the form of density dependence. We give simple criteria for the success of the invading species on dimensionless quantities involving rates of ecosystem engineering and of habitat degradation. The model's predictions offer an additional explanation for a range of invasion dynamics reported in the literature, including lag times between introduction and establishment. One intriguing result is that a series of failed invasions may successively reduce environmental resistance to subsequent invasion, through a cumulative effect of habitat transformation. More work is needed to determine the frequency and conditions in which engineering is required for successful establishment, and whether highly-successful (or high-impact) invaders are more likely to possess ecosystem engineering traits. [source] Mechanisms of resistance to invasion in a California grassland: the roles of competitor identity, resource availability, and environmental gradientsOIKOS, Issue 1 2007Meredith A. Thomsen Resistance to the invasion of exotic plants may sometimes result from the strong effects of a relatively small number of resident species. Understanding the mechanisms by which such species resist invasion could provide important insights for the management of invaded ecosystems. Furthermore, the individualistic responses of community members to resource availability and environmental gradients could drive spatial variation in resistance at the local to landscape scales. We tested the resistance of monoculture plots of three native perennial grasses from the California coastal prairie to the invasion of the European perennial grass Holcus lanatus. We also used a watering treatment that increased early summer water availability and a natural elevational gradient in resource availability and soil texture to evaluate how resident identity interacted with abiotic resistance to affect Holcus establishment. Two native species, Festuca rubra and Calamagrostis nutkaensis, exhibited strong resistance, correlated with their negative effects on light availability. A third native grass, Bromus carinatus var. maritimus, had either no effect or a weakly facultative effect on Holcus performance relative to bare plots. Water addition did not alter the resistance of these species, but the elevation gradient did. Holcus invasion increased with improving abiotic conditions towards the slope bottom in bare and Bromus plots, but invasion decreased towards the bottom in Calamagrostis plots, where better conditions favored competitive residents. These results support the idea that resistance to invasion can sometimes be due to a subset of native species, and that the resistance provided by even a single species is likely to vary across the landscape. Identifying the mechanisms by which species resist invasion could facilitate the selection of management strategies that at best increase, or at worst do not decrease, natural resistance. [source] Female-biased dispersal, low female recruitment, unpaired males, and the extinction of small and isolated bird populationsOIKOS, Issue 2 2001Svein Dale Small and isolated populations are usually assumed to be at a high risk of extinction due to environmental or demographic stochasticity, genetic problems, or too little immigration. In birds, natal dispersal is usually female-biased, but the consequences of such a pattern on vulnerability to extinction of isolated populations has not received much attention before. In this paper I derive predictions as to how female-biased natal dispersal may differentially affect the extinction risk of populations and species with contrasting distributions, migratory behaviours, life histories and mating systems. Female-biased dispersal will lead to male-biased sex ratios in small, isolated or fragmented populations, in particular because recent research has shown that females often have a limited ability to search for mates and may therefore effectively be lost from the breeding population if they disperse into areas empty of conspecifics. I reviewed published studies on birds and found that a high proportion of unpaired males is common in isolated populations or populations in small habitat fragments. Dispersal of females may therefore increase the vulnerability to extinction of small or isolated populations, or populations at the periphery of a species' distribution range. I also predict that vulnerability to extinction should be greater for migratory than for resident species and greater for short-lived than for long-lived species because of differences in the time available for females to locate unpaired males. Further, extinction risk may also be greater for birds than for mammals due to differences in which sex disperses and patterns of parental care. Finally, mating system will also affect vulnerability to extinction when natal dispersal leads to biased sex ratios. I review available evidence for these predictions (e.g. songbird declines in North America) and discuss implications for conservation. [source] Does disturbance, competition or resource limitation underlie Hieracium lepidulum invasion in New Zealand?AUSTRAL ECOLOGY, Issue 3 2010Mechanisms of establishment, functional differentiation among invasive, native species, persistence Abstract The processes underlying plant invasions have been the subject of much ecological research. Understanding mechanisms of plant invasions are difficult to elucidate from observations, yet are crucial for ecological management of invasions. Hieracium lepidulum, an asteraceous invader in New Zealand, is a species for which several explanatory mechanisms can be raised. Alternative mechanisms, including competitive dominance, disturbance of resident vegetation allowing competitive release or nutrient resource limitation reducing competition with the invader are raised to explain invasion. We tested these hypotheses in two field experiments which manipulated competitive, disturbance and nutrient environments in pre-invasion and post-invasion vegetation. H. lepidulum and resident responses to environmental treatments were measured to allow interpretation of underlying mechanisms of establishment and persistence. We found that H. lepidulum differed in functional response profile from native species. We also found that other exotic invaders at the sites were functionally different to H. lepidulum in their responses. These data support the hypothesis that different invaders use different invasion mechanisms from one another. These data also suggest that functional differentiation between invaders and native resident vegetation may be an important contributing factor allowing invasion. H. lepidulum appeared to have little direct competitive effect on post-invasion vegetation, suggesting that competition was not a dominant mechanism maintaining its persistence. There was weak support for disturbance allowing initial establishment of H. lepidulum in pre-invasion vegetation, but disturbance did not lead to invader dominance. Strong support for nutrient limitation of resident species was provided by the rapid competitive responses with added nutrients despite presence of H. lepidulum. Rapid competitive suppression of H. lepidulum once nutrient limitation was alleviated suggests that nutrient limitation may be an important process allowing the invader to dominate. Possible roles of historical site degradation and/or invader-induced soil chemical/microbial changes in nutrient availability are discussed. [source] Pattern and process in the distribution of North American freshwater fishBIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 1 2010DAVID GRIFFITHS Published species lists were analysed to determine the contributions of dispersal, habitat preference, river channel size, body size, and glacial history to large-scale patterns in freshwater fish species richness in North America, north of central Mexico. Total species richness declines to the north and west but the pattern for endemics differs from that of widespread species. Mississippi Basin regions are more species rich than more isolated, coastal, regions. Richness declines more rapidly with increasing latitude in riverine specialist than in habitat generalist species. Levels of endemism are greatest in species found in small- to medium-sized river channels. The strong Rapoport effect, more marked in migratory than resident species, is correlated with habitat preference, channel size, and glacial history. Body size increases with latitude, largely as a result of a trend from small resident to large migrant species. In unglaciated regions, ancestral species survived in large habitats because these are longer-lived, more extensive, less isolated and more stable than headwaters, permitting larger populations and lower extinction levels. Reduced levels of gene flow in small, peripheral, channels isolated by larger downstream habitats have resulted in the production of many, small range, small-bodied species. The latitudinal richness gradient is a consequence of speciation and extinction events in unglaciated faunas and an increasing domination of faunas by generalist, large bodied, large channel, recolonizing species in more northern regions. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100, 46,61. [source] | ||||||||||