Geographical distributions of spiny pocket mice in South America: insights from predictive models

Aim Predictive models of species’ distributions use occurrence records and environmental data to produce a model of the species’ requirements and a map of its potential distribution. To determine regions of suitable environmental conditions and assess biogeographical questions regarding their ranges, we modelled the potential geographical distributions of two spiny pocket mice (Rodentia: Heteromyidae) in north‐western South America. Location North‐western South America. Methods We used the Genetic Algorithm for Rule‐Set Prediction (GARP), environmental data from GIS maps and georeferenced collection localities from a recent systematic review of Heteromys australis and H. anomalus to produce the models. Results GARP models indicate the potential presence of H. australis throughout mesic montane regions of north‐western South America, as well as in some lowland regions of moderately high precipitation. In contrast, H. anomalus is predicted to occur primarily in drier areas of the Caribbean coast and rain‐shadowed valleys of the Andes. Conclusions The models support the disjunct status of the population of H. australis in the Cordillera de Mérida, but predict a continuous distribution between known populations of H. anomalus in the upper Magdalena Valley and the Caribbean coast. Regions of suitable environmental conditions exist disjunct from known distributional areas for both species, suggesting possible historical restrictions to their ranges. This technique holds wide application to other study systems.     

Are hybrid species more fit than ancestral parent species in the current hybrid species habitats?

Hybrid speciation is thought to be facilitated by escape of early generation hybrids into new habitats, subsequent environmental selection and adaptation. Here, we ask whether two homoploid hybrid plant species (Helianthus anomalus, H. deserticola) diverged sufficiently from their ancestral parent species (H. annuus, H. petiolaris) during hybrid speciation so that they are more fit than the parent species in hybrid species habitats. Hybrid and parental species were reciprocally transplanted into hybrid and parental habitats. Helianthus anomalus was more fit than parental species in the H. anomalus actively moving desert dune habitat. The abilities to tolerate burial and excavation and to obtain nutrients appear to be important for success in the H. anomalus habitat. In contrast, H. deserticola failed to outperform the parental species in the H. deserticola stabilized desert dune habitat, and several possible explanations are discussed. The home site advantage of H. anomalus is consistent with environmental selection having been a mechanism for adaptive divergence and hybrid speciation and supports the use of H. anomalus as a valuable system for further assessment of environmental selection and adaptive traits.     

Altitudinal segregation between Ural Owl Strix uralensis and Tawny Owl S. aluco: evidence for competitive exclusion in raptorial birds

Capsule The Owls were significantly segregated in space with the most important factor being altitude.

Aims To establish if the segregation between Ural and Tawny Owl on the level of habitat selection is due to different habitat requirements of the species or a consequence of competitive exclusion.

Methods Seven variables were recorded for habitat of Ural Owls, Tawny Owls that live in sympatry with Ural Owls and Tawny Owls that live in allopatry with Ural Owls. Data were gathered in five mountain areas covered with similar continuous montane forest inside and outside known Ural Owl distribution in Slovenia. Owl territories were surveyed in 2001 using playback method. Evidence for segregation was searched for using discriminant function analysis.

Results The altitudinal distribution of Tawny Owls sympatric to Ural Owls was restricted to low elevations with Ural Owls at high elevations. Where Ural Owls were absent, Tawny Owls widened the altitudinal part of their ecological niche to the mountaintop.

Conclusion Segregation between Tawny and Ural Owls is due to competitive exclusion, with the less competitive Tawny Owl being out-competed by the superior Ural Owl. The forests at foothills are influenced by human presence and therefore avoided by Ural Owls. In areas where both species live in sympatry, these areas act as refugia for Tawny Owls.     

Behavioral and Physiological Differences between Two Parapatric Heliconius Species1

The behavior and physiology of two parapatric sibling species, i Heliconius erato cyrbia Godt. and H. himera Hew., were investigated to assess if environmental adaptation enabled stable morphological, genetic, and ecological differences to exist in the face of hybridization. Morning and evening activity, egg production, and larval development time of H. himera and H. erato in insectaries were recorded; individuals were collected in allopatry and in sympatry from a hybrid zone in which the species overlapped. Studies were performed at ambient conditions within the natural range of H. himera. H. himera was considerably more active than H, erato flying earlier in the morning and later in the evening, even when both species were collected in sympatry. Similarly, H. himera laid more eggs, and the hatched larvae developed more rapidly. The results suggest that physiological constraints are an important selective force that may have been important in speciation and counteracts hybridization in the maintenance of the H. himeral H. erato contact zone. Ecological selection, arising from adaptation to low temperatures, may help explain the competitive exclusion of H. erato by H. himera in the drier, cooler montane habitat favored by the latter species.     

Asymmetric and frequency‐dependent pollinator‐mediated interactions may influence competitive displacement in two vernal pool plants

A plant species immigrating into a community may experience a rarity disadvantage due to competition for the services of pollinators. These negative reproductive interactions have the potential to lead to competitive displacement or exclusion of a species from a site. In this study, we used one‐ and two‐species arrays of potted plants to test for density and frequency dependence in pollinator‐mediated and above‐ground intraspecific and interspecific competition between two species of Limnanthes that have overlapping ranges, but rarely occur in close sympatry. There were asymmetric competitive effects; the species responded differently to their frequency within 16‐plant replacement series arrays. Limnanthes douglasii rosea experienced stronger reductions in lifetime and per‐flower fertility, likely due to pollinator‐mediated competition with Limnanthes alba. This effect may be linked to asymmetrical competition through heterospecific pollen transfer. This study demonstrates that pollinator‐mediated competition may discourage establishment of L. d. rosea in sites already occupied by its congener.     

Plasticity of Lythrum salicaria and Phragmites australis growth characteristics across a European geographical gradient

Plants of Lythrum salicaria and Phragmites australis originating from localities across the European north–south geographical gradient were cultivated in parallel in an outdoor tub experiment. A strong correlation was found between growth and morphometric characteristics related to plant size (plant height, basal diameter, aboveground- and belowground plant biomass, etc.) and the position of the respective populations along the north–south gradient. Plants of both L. salicaria and P. australis from the southern localities grew taller and more vigorously and flowered later than plants from relatively more northern localities. From this point of view, the plants originating from south European populations were comparable to invasive North American plants. Our study indicates that explanation of the competitive success of populations invading new geographical areas may involve the role of geographic gradients within the species native range.     

Global distribution patterns provide evidence of niche shift by the introduced African dung beetle Digitonthophagus gazella

The establishment of cattle ranches throughout the world has prompted the release of dung beetles as biological control agents that reduce pasture fouling and control dung-breeding flies. One of these beetles, Digitonthophagus gazella (Fabricius) (Coleoptera: Scarabaeidae), that is native to southeast Africa, has been introduced into the Americas, Australia, and New Zealand. Distribution records for this species have been used to develop climate models of potential future establishment. Recent studies, however, identify D. gazella as a complex of seven species. Taking into account this revision, and the clear identification of the records belonging to the actual D. gazella, we developed environmental models to identify factors that have contributed to the establishment of this species across regions and habitats. We compared the environmental conditions of D. gazella in its native range against those in the regions where the species has or has not established. Our results indicate that D. gazella is still absent in certain parts of Central and South America and parts of Africa where it could potentially establish. We speculate that its distribution in Africa is limited by competitive exclusion. The introduction of D. gazella in America is relatively recent, such that the full extent of its distribution has probably yet to be realized. In Australia and North America, D. gazella is present in regions not predicted according to its native environmental conditions. This discrepancy may reflect a lack of competitive exclusion, phenotypic plasticity, and/or genetic adaptation. Our analyses suggest that the species has the ability to adapt to a wide range of environmental conditions that are extremely different from those in their native region. The species represents a useful case study to indicate that an introduced species may expand its realized niche beyond what is expected based on apparent environmental limits in the species native range.     

GIS-based niche models identify environmental correlates sustaining a contact zone between three species of European vipers

The current range of European vipers is mostly parapatric but local‐scale allopatric distribution is common and few cases of sympatry are known. In the High Course of Ebro River, northern Spain, there is a contact zone between Vipera aspis, V. latastei, and V. seoanei. Sympatry was detected between aspis and latastei and also specimens with intermediate morphological traits. Presence‐data at a local scale (1 × 1 km) and ecological niche‐based models manipulated in a GIS were used to (1) identify how environmental factors correlate with the distribution of the three vipers and with the location of the sympatry area, and (2) identify potential areas for viper occurrence and sympatry. Ensemble for casting with 10 Maximum Entropy models identified a mixture of topographical (altitude, slope), climatic (precipitation, evapotranspiration, and minimum and maximum temperature), and habitat factors (land cover) as predictors for viper occurrence. Similar predicted probabilities according to the variation of some environmental factors (indicating probable sympatry) were observed only for aspis‐latastei and aspis‐seoanei. In fact, areas of probable occurrence of vipers were generally allopatric but probable sympatry between vipers was identified for aspis‐latastei in 76 UTM 1 × 1 km squares, for aspis‐seoanei in 23 squares, and latastei‐seoanei in two squares. Environmental factors correlate with the location of this contact zone by shaping the species range: some enhance spatial exclusion and constrain distribution to spatially non‐overlapping ranges, while others allow contact between species. The distribution in the contact zone apparently results from the balance between the pressures exerted by the different environmental factors and in the sympatry area probably by interspecific competition. Further ecological and genetical data are needed to evaluate the dynamics of the probable hybrid zone. GIS and niche‐modelling tools proved to be powerful tools to identify environmental factors sustaining the location of contact zones.     

Interactions between native and invasive gecko lizards in tropical Australia

Invasive geckos of the genus Hemidactylus (Gekkonidae) are spreading rapidly through urban environments in many tropical and subtropical parts of the world. The invaders have caused rapid declines in native gecko abundance in some areas, but their interactions with Australian native species remain unknown. In a small rural village near Darwin, we found that Hemidactylus frenatus is abundant around both lighted and unlighted buildings, but rarely found in surrounding bushland. It is sympatric with the larger Gehyra australis (Gekkonidae) in this disturbed site, and often forages on the same buildings, but is active mostly during the dry‐season (vs. wet‐season for G. australis) and is competitively subordinate to the larger native species. In laboratory encounters, H. frenatus fled from G. australis, and modified its refuge‐site use in the presence of the native lizard. In those same trials, the native gecko often attacked and rarely fled; and did not shift its refuge‐site selection. In field surveys, the two taxa frequently co‐occurred. However, substrate use of the invasive H. frenatus was modified by the presence of the native G. australis, consistent with competitive displacement. Our counts of H. frenatus were highest during the dry‐season, when G. australis (like most other small native reptiles) is relatively inactive. The invasive gecko thus appears to be exploiting a ‘vacant niche’ around buildings, rather than displacing the native gecko taxon. This outcome may reflect the size disparity between the native species and the invader; Hemidactylus frenatus may well have significant ecological impacts on smaller native lizards.     

Can environmental fluctuation prevent competitive exclusion in sympatric flycatchers?

Ecology has been characterized by a central controversy for decades: namely, whether the distribution and abundance of organisms are determined by species interactions, such as competitive exclusion, or by environmental conditions. In part, this is because competitive exclusion has not been convincingly demonstrated in open, natural systems. In addition, traditional theoretical models cannot predict the outcome of competitive interactions in the presence of environmental variability. In this paper we document the limiting influence of strong interspecific competition on population dynamics and nestling mortality in a mixed population of pied flycatchers (Ficedula hypoleuca) and collared flycatchers (F. albicollis in a narrow zone of sympatry. Whereas the former species was limited mainly by interspecific competition, the latter species was limited by the concerted influences of intraspecific competition and climate. The analysis suggests a march towards competitive exclusion of the pied flycatcher during warm periods. However, competitive exclusion is apparently prohibited on a local scale because intraspecific competition among individual collared flycatchers intensifies when they are forced to cope with severe environmental conditions, promoting the temporary and local presence of pied flycatchers.     

Biogeography,macroecology and species' traits mediate competitive interactions in the order Lagomorpha

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Effects of growing conditions on the growth of and interactions between salt marsh plants: implications for invasibility of habitats

A common but often less tested explanation for the successful invasion of alien species is that invasive alien species outcompete their co-occurring natives, which may not always be the case. In this study, we established artificial environmental gradients in a series of pot experiments with controlled environments to investigate the effects of salinity, sediment type and waterlogging on the performance of and interactions between Phragmites australis (native) and Spartina alterniflora (alien), which generally co-exist in the saline intertidal zones of Chinese and American coasts. Significant effects of salinity and waterlogging were detected on biomass production and morphological characteristics of S. alterniflora and P. australis, and the competitive interactions between the two species were found to vary with all three environmental factors in our experiments. Relative Neighbor Effect (RNE) analyses indicate that competitive dominance of S. alterniflora occurred under the conditions of high salinity, sandy sediment and full immersion, whereas P. australis showed competitive dominance under the conditions of low salinity and non-immersion. Our results suggest that S. alterniflora might outcompete P. australis under conditions present in early salt marsh succession, which support the viewpoint that the outcomes of competition between co-occurring native and invasive alien plants depend on the growing conditions. The implication of this study is that in response to the environmental changes expected from seawater intrusion and sea-level rise, the range of S. alterniflora is expected to expand further in the Yangtze River estuary in the future.     

Abundance of Bemisia tabaci Gennadius (Hemiptera: Aleyrodidae) and its parasitoids on vegetables and cassava plants in Burkina Faso (West Africa)

The whitefly Bemisia tabaci is a pest of many agricultural and ornamental crops worldwide and particularly in Africa. It is a complex of cryptic species, which is extremely polyphagous with hundreds of host plants identified around the world. Previous surveys in western Africa indicated the presence of two biotypes of the invasive MED species (MED‐Q1 and MED‐Q3) living in sympatry with the African species SSA and ASL. This situation constitutes one of the rare cases of local coexistence of various genetic entities within the B. tabaci complex. In order to study the dynamics of the distribution and abundance of genetic entities within this community and to identify potential factors that could contribute to coexistence, we sampled B. tabaci populations in Burkina Faso in 2015 and 2016 on various plants, and also their parasitoids. All four genetic entities were still recorded, indicating no exclusion of local species by the MED species. While B. tabaci individuals were found on 55 plant species belonging to eighteen (18) families showing the high polyphagy of this pest, some species/biotypes exhibited higher specificity. Two parasitoid species (Eretmocerus mundus and Encarsia vandrieschei) were also recorded with E. mundus being predominant in most localities and on most plants. Our data indicated that whitefly abundance, diversity, and rate of parasitism varied according to areas, plants, and years, but that parasitism rate was globally highly correlated with whitefly abundance suggesting density dependence. Our results also suggest dynamic variation in the local diversity of B. tabaci species/biotypes from 1 year to the other, specifically with MED‐Q1 and ASL species. This work provides relevant information on the nature of plant–B. tabaci‐parasitoid interactions in West Africa and identifies that coexistence might be stabilized by niche differentiation for some genetic entities. However, MED‐Q1 and ASL show extensive niche overlap, which could ultimately lead to competitive exclusion.     

The effect of the extent of the study region on GIS models of species geographic distributions and estimates of niche evolution: preliminary tests with montane rodents (genus Nephelomys) in Venezuela

Aim Various techniques model a species’ niche and potential distribution by comparing the environmental conditions of occurrence localities with those of the overall study region (via a background or pseudoabsence sample). Here, we examine how changes in the extent of the study region (ignored or under‐appreciated in most studies) affect models of two rodents, Nephelomys caracolus and Nephelomys meridensis. Location North‐central South America. Methods We used Maxent to model the species' potential distributions via two methods of defining the study region. In Method 1 (typical of most studies to date), we calibrated the model in a large study region that included the ranges of both species. In Method 2, we calibrated the model using a smaller study region surrounding the localities of the focal species, and then applied it to the larger region. Because the study region of Method 1 is likely to include areas of suitable conditions that are unoccupied because of dispersal limitations and/or biotic interactions, this approach is prone to overfitting to conditions found near the occupied localities. In contrast, Method 2 should avoid such problems but may require further assumptions (‘clamping’ in Maxent ) to make predictions for areas with environmental conditions beyond those found in the smaller study region. For each method, we calculated several measures of geographic interpredictivity between predictions for the species (cross‐species AUC, cross‐species omission rate, and proportional geographic overlap). Results Compared with Method 1, Method 2 revealed a larger predicted area for each species, less concentrated around known localities (especially for N. caracolus). It also led to higher cross‐species AUC values, lower cross‐species omission rates and higher proportions of geographic overlap. Clamping was minimal and occurred primarily in regions unlikely to be suitable. Main conclusions Method 2 led to more realistic predictions and higher estimates of niche conservatism. Conclusions reached by many studies depend on the selection of an appropriate study region. Although detailed information regarding dispersal limitations and/or biotic interactions will typically be difficult to obtain, consideration of coarse distributional patterns, topography and vegetational zones often should permit delimitation of a much more reasonable study region than the extremely large ones currently in common use.     

Population‐level dynamics in experimental mixed infections: evidence for competitive exclusion among bacterial parasites of Paramecium caudatum

Parasites frequently share their host populations with other parasites. However, little is known about how different parasites respond to competition with diverse competitor species in the within‐host and between‐host environments. We explored the repeatability of competition by simultaneously exposing microcosm populations of the ciliate Paramecium caudatum to pairs of parasites from the Holospora species complex (H. undulata, H. caryophila and H. obtusa). We measured how competition affected the persistence and prevalence of each compared to single infections, across three host genotypes. Three weeks post‐inoculation we identified the presence of each parasite using fluorescence in situ hybridisation (FISH). Competitive exclusion (62/72) was more common than co‐existence (10/72) in populations inoculated with two parasites. There was a clear pattern of competitive superiority, with H. caryophila persisting in all doubly inoculated populations (with either H. undulata or H. obtusa), and H. undulata tending to exclude H. obtusa. This mirrored infection success in single infections, with H. caryophila having a higher infection prevalence in single inoculations, followed by H. undulata then H. obtusa. The probability of persistence in co‐inoculations did not change across the different host genotypes, and prevalence was the same as in single infections. Our results are consistent with superinfection models, which assume the competitive exclusion of parasites upon contact within the same host. Furthermore, such non‐random competitive epidemiological dynamics, where one parasite always wins, may be of interest for public health management, especially if the winning parasite is avirulent, as is seemingly the case here.     

Effect of competition on habitat utilization in two temperate climate gecko species

Competition over spatial niche utilisation is one of most common competitive interactions between species in sympatry. Moreover, competitive interactions may involve age classes, and can fluctuate temporally. Consequently, evasive strategies that enable co-existence are likely to be important in the evolution of species assemblages. Here we investigate a system of two co-existing species of temperate geckos with similar ecologies (the house gecko, Hemidactylus turcicus and the wall gecko, Tarentola mauritanica), providing an opportunity to study the effect of species interactions. Juveniles and adults of both species were investigated throughout their daily and annual cycle to explore the effect of inter- and intra-specific interactions on microhabitat use. The two species showed differences in habitat use for both age classes in sympatry. In sympatry, T. mauritanica uses more open habitats and is more active. In contrast, H. turcicus is found in more closed habitats, closer to the ground and to vegetation cover. In allopatry, H. turcicus was observed in more open habitats, closer to the ground, and to vegetation cover, when compared to the population in sympatry with T. mauritanica. These differences in habitat usage were significant for both age classes. Moreover, there were differences, both in sympatry and in allopatry, between age classes that were dependent on season. In conclusion, the presence of a competitor induces a spatial shift in individuals of both age classes of H. turcicus. Observed plasticity in habitat utilisation in both age classes of H. turcicus is used to argue for the invasive potential of this species.     

Predicting the potential invasive range of light brown apple moth (Epiphyas postvittana) using biologically informed and correlative species distribution models

The light brown apple moth (Epiphyas postvittana) is a highly polyphagous species that has invaded several geographic regions across the globe and has stimulated substantial concern over possible impacts for agriculture in the US. We aimed to predict the potential geographic range of E. postvittana to better understand the threat of this species in the US and globally. We used the mechanistic simulation modelling method CLIMEX and the correlative niche modelling method Maxent to predict the geographic distribution of E. postvittana in its native range and globally and tested model projections using known invasion data. Different predictor variable data sets and threshold dependent and independent measures of environmental suitability were considered in model evaluation. Models accurately predicted known invasive localities of E. postvittana across the globe. Overall predictions of environmental suitability were largely congruent across models, although there were some notable differences. Ephiphyas postvittana clearly has the potential to establish in many regions of the globe, although some previous analyses of the potential distribution of this species appear overly pessimistic. Additional studies of the biology of this species in invaded areas, including interactions with natural enemies and the capacity to adapt to novel climatic conditions, are ultimately needed to more fully understand its potential economic and environmental impacts.     

Effects of phosphorus on growth and competitive interactions of native and introduced species found in White Box woodlands

Abstract White Box (Eucalyptus albens Benth.) woodlands are among Australia's most endangered ecosystems and are threatened by exotic species invasion. There is evidence from other Australian communities that phosphorus enrichment can facilitate invasion, and differential growth of native and exotic species under increased phosphorus is a possible mechanism. Two glasshouse experiments were designed to test the following three questions relating to species responses to phosphorus: (i) do exotic and native species have different patterns of growth along a gradient of increasing phosphorus?; (ii) do exotic species have a greater competitive effect on native species than do conspecifics?; (iii) does phosphorus enrichment compound the competitive effect of exotic species on native species? Four native perennial species (Themeda australis (R. Br.) Staph., Bothriochloa macra (Steud.) S. T. Blake, Austrodanthonia racemosa (R. Br.) H. P. Linder and Eucalyptus albens) and two exotic annual species (Vulpia bromoides (L) Gray and Echium plantagineum L) were used. In the first experiment, plants were grown individually under six levels of soil phosphorus ranging from 0 to 60 p.p.m. In the second experiment, individuals of Eucalyptus albens and B. macra were grown alone, with a conspecific competitor, or with an exotic (V. bromoides or Echium plantagineum) competitor under low (10 p.p.m.) and high (100 p.p.m.) phosphorus. Both exotic species showed a greater positive response to increased phosphorus than the native species in experiment 1, and Eucalyptus albens seedlings grown with Echium plantagineum were significantly smaller than individuals grown alone or with Eucalyptus albens in experiment 2. There was no evidence that high phosphorus increased the competitive effect of the exotic species, but the combination of a strong positive response to phosphorus and a strong effect on growth of a native species indicates that phosphorus enrichment could favour exotic species in woodland remnants and that field studies testing the effect of phosphorus in a broader context would be appropriate.     

Coexistence of ecologically similar colonising species. II. Population differentiation in Drosophila aldrichi and D. Buzzatii for competitive effects and responses at different temperatures and allozyme variation in D. aldrichi

Drosophila aldrichi and D. buzzatii are cactophilic species that colonised Australia about 55–60 years ago. They are sympatric only in Australia. Thus they may be in the process of adapting to new environments and to each other, and diversifying among local, possibly isolated, populations. Larval competitive effects for three populations of each species (Roma, Planet Downs, and Binjour) were measured on semi-natural cactus rots at three temperatures, with preadult viability, developmental time and adult body weight scored for each sex and species. Populations of both species varied in their responses to the other species as competitor, and one D. buzzatii population (Roma) reduced larval performance of D. aldrichi significantly more than did other D. buzzatii populations. Geographic divergence for the three traits was similar in both species, with a relative performance index derived from these traits highest for Roma, second for Binjour, and least for the Planet Downs population of each species. The Roma D. aldrichi population was the most different from the other populations for the performance index and in terms of genetic distances derived from allozyme frequencies. Additionally, comparisons of climatic variables among the population localities showed that the Roma environment was most different from the others. Differential natural selection in different areas of the cactus distribution may be a major cause of population divergence in both species. Drosophila aldrichi is superior for some fitness components at the highest temperature. Thus temperature variation throughout the cactus distribution may contribute to the different ranges of these two species, with competitive exclusion of D. aldrichi in the southern, cooler region of the cactus distribution, but coexistence in the northern, warmer region.