Effects Of Spatial Isolation Research Articles

Lone male loser? Effects of spatial isolation on male pairing success in the Ortolan Bunting (Emberiza hortulana)

Cover photo: Male Ortolan Bunting. Photo: Frode Falkenberg. In small, isolated or fragmented bird populations, past studies have shown that there can be a high proportion of unpaired males. Low male pairing success is suggested to be the result of female-biased natal dispersal and low female recruitment. Indirect evidence indicates that such an effect operates among populations with different degrees of isolation, but little is known of how isolation affects male pairing success within populations. The Norwegian population of Ortolan Buntings (Emberiza hortulana) is distributed in about 50 discrete patches in an area of nearly 500 km2. In this study, we examined whether patch isolation and individual male isolation affected male pairing success. The population has a strongly male-biased sex ratio, with almost half of all males being unpaired. We found that male pairing successs was negatively related to isolation of patches and isolation of individual males in most analyses, and with significant effects in particular in some analyses of individual isolation. Patch population size was measured as the total number of males observed in a particular patch in a specific year and did not have an effect on male pairing success, and was not related to patch isolation. Even though some tests were statistically significant, the magnitude of effects were small and there was large variance in male pairing success. Variance in success suggests that other factors than isolation such as male age or experience may be just as important for male fitness within our study population. Furthermore, we suggest that small effects of isolation were due to the ability of Ortolan Buntings to move large distances within the breeding season, and that isolation effects on small spatial scales are more likely for species with restricted dispersal, such as resident species or species with high population density.

Social isolation affects intra-specific interaction behaviour and reduces the size of the cerebellar brain region in juvenile Atlantic salmon Salmo salar.

The social environment can affect the development of behavioural phenotypes in fish, and it is important to understand such effects when rearing fish in artificial environments. Here, the authors test the effects of spatial isolation on social interaction propensity and brain development in hatchery‐reared Atlantic salmon Salmo salar L. Salmon reared in isolation generally stayed further away from a conspecific in a standardized intruder test than conspecifics reared together in groups. Isolated salmon also tended to be more active in an intruder test, albeit non‐significantly so, but this pattern was not detected in open‐field tests without an intruding conspecific. The cerebellar brain region was relatively smaller in isolated salmon, suggesting that the brain was developing differently in these fish. Therefore, some features of the behavioural and neural phenotype are affected by rearing in isolation. These effects should be considered when rearing salmon, particularly for experimental purposes as it may affect results of laboratory studies on behavioural expression and brain size.

Top predator introduction changes the effects of spatial isolation on freshwater community structure.

Current conceptual metacommunity models predict that the consequences of local selective pressures on community structure increase with spatial isolation when species favored by local conditions also have higher dispersal rates. This appears to be the case of freshwater insects in the presence of fish. The introduction of predatory fish can produce trophic cascades in freshwater habitats because fish tend to prey upon intermediate predatory taxa, such as predatory insects, indirectly benefiting herbivores and detritivores. Similarly, spatial isolation can limit dispersal and colonization rates of predatory insects more strongly than of herbivores and detritivores, thus generating similar cascading effects. Here we tested the hypothesis that the effect of introduced predatory fish on insect community structure increases with spatial isolation by conducting a field experiment in artificial ponds that manipulated the presence/absence of fish (the redbreast tilapia) at three different distances from a source wetland. Our results showed that fish have direct negative effects on the abundance of predatory insects but probably have variable net effects on the abundance of herbivores and detritivores because the direct negative effects of predation by fish may offset indirect positive ones. Spatial isolation also resulted in indirect positive effects on the abundance of herbivores and detritivores but this effect was stronger in the absence rather than in the presence of fish so that insect communities diverged more strongly between fish and fishless ponds at higher spatial isolation. We argue that an important additional mechanism, ignored in our initial hypothesis, was that as spatial isolation increases fish predation pressure upon herbivores and detritivores increases due to the relative scarcity of predatory insects, thus dampening the positive effect that spatial isolation confers to lower trophic levels. Our results highlight the importance of considering interspecific variation in dispersal and multiple trophic levels to better understand the processes generating community and metacommunity patterns.

Estimation of the Genetic Structure of Helix pomatia L. Populations (Mollusca, Pulmonata) by Capillary Electrophoresis of ISSR DNA Fragments

Using the capillary electrophoresis of ISSR DNA fragments, the genetic structure of the adventitious populations of Helix pomatia L. (Mollusca, Pulmonata) inhabiting the territory of Eastern Europe was studied. A significant decrease in genetic heterogeneity (He = 0.095 ± 0.002) and population differentiation level (Fst = 0.074) was revealed in comparison with similar data obtained using the ISSR method with electrophoretic detection in agarose gel and allozymes in polyacrylamide gel. Similar to other methods, an effect of spatial isolation (RM =–0.476) was found on the basis of regression analysis between genetic and geographical distances. The effective population size, calculated with the help of M. Slatkin’s model, turned out to be the largest of the previously calculated values (Ne = 41.8), which indicates the high viability of the studied groups of Roman snails in newly developed territories.

Military training areas as refuges for threatened dragonfly species: Effect of spatial isolation and military activity

A long-term decline in habitat quality and freshwater species diversity has forced conservation managers to consider secondary habitats, such as military training areas (MTAs), that were previously overlooked but have conservation potential. Isolation from many negative anthropogenic influences combined with disturbances associated with military activities can benefit the diversity of terrestrial species. However, little is known about the conservation potential of freshwater habitats that are an integral part of MTAs. In this study, we used dragonflies and damselflies as valuable indicators of habitat quality to compare the diversity of freshwater sites inside and outside MTAs. We randomly selected 16 sites inside four extensive MTAs and 16 reference sites outside MTAs and examined the differences in traits of species occurring inside and outside the MTAs. We found that the diversity and conservation value of dragonfly communities inside MTAs was comparable to that in the most valuable freshwater habitats outside MTAs. Inside MTAs, species were primarily those associated with habitats in the late successional stages, while species associated with early successional stages were absent. Undoubtedly, the conservation potential of MTAs for freshwater invertebrates is in the long-term isolation from negative anthropogenic influences. Paradoxically, the main potential problem in protecting freshwater habitats inside MTAs is the cessation of military activity.

Species and Phylogenetic Heterogeneity in Visitation Affects Reproductive Success in an Island System

Plant-pollinator mutualisms can be disrupted in fragmented and isolated populations. Isolated populations attract fewer and less diverse pollinators, but it is not generally known whether this is due to reductions in the abundance and/or diversity of flowers at a site or to the biogeography of pollinators (or both). Islands represent one system potentially suitable to analyze the effects of spatial isolation. Here, we examine the contribution that differences in visitor composition make to increased selfing and seed production by examining the major visitors to Plectritis congesta in populations on the Gulf Islands and Vancouver Island. We find that (1) connectivity is more strongly associated with visitor assemblages and seed production than components of the floral community and (2) taking phylogeny into account suggests that increased visitation by solitary bees as opposed to other functional groups increases female fitness in P. congesta.

Latitudinal environmental niches and riverine barriers shaped the phylogeography of the Central Chilean endemic Dioscorea humilis (Dioscoreaceae).

The effects of Pleistocene glaciations and geographical barriers on the phylogeographic patterns of lowland plant species in Mediterranean-climate areas of Central Chile are poorly understood. We used Dioscorea humilis (Dioscoreaceae), a dioecious geophyte extending 530 km from the Valparaíso to the Bío-Bío Regions, as a case study to disentangle the spatio-temporal evolution of populations in conjunction with latitudinal environmental changes since the Last Inter-Glacial (LIG) to the present. We used nuclear microsatellite loci, chloroplast (cpDNA) sequences and environmental niche modelling (ENM) to construct current and past scenarios from bioclimatic and geographical variables and to infer the evolutionary history of the taxa. We found strong genetic differentiation at nuclear microsatellite loci between the two subspecies of D. humilis, probably predating the LIG. Bayesian analyses of population structure revealed strong genetic differentiation of the widespread D. humilis subsp. humilis into northern and southern population groups, separated by the Maipo river. ENM revealed that the ecological niche differentiation of both groups have been maintained up to present times although their respective geographical distributions apparently fluctuated in concert with the climatic oscillations of the Last Glacial Maximum (LGM) and the Holocene. Genetic data revealed signatures of eastern and western postglacial expansion of the northern populations from the central Chilean depression, whereas the southern ones experienced a rapid southward expansion after the LGM. This study describes the complex evolutionary histories of lowland Mediterranean Chilean plants mediated by the summed effects of spatial isolation caused by riverine geographical barriers and the climatic changes of the Quaternary.

Spatial isolation slows down directional plant functional group assembly in restored semi‐natural grasslands

SummaryEcological restoration schemes often assume that after reinstating appropriate abiotic conditions, plant communities will assemble following a single predictable pathway towards a fixed target state. This idea has recently been challenged, with increasing evidence that plant community assembly can only be considered deterministic at the plant trait level, rather than at the species level, and that the assembly outcome is largely influenced by the spatial context of the restoration site.We surveyed 147 vegetation plots across a chronosequence of 22 restored semi‐natural grassland patches to quantify the effects of spatial isolation on both plant species and plant trait assembly. Trait level assembly was analysed using an emergent group approach, based on 28 functional plant traits. Additionally, we examined the effects of several dispersal‐related plant traits on species recolonization capacities.Whereas total plant species richness of the restoration patches did not change through space or through time, progressing assembly was found to consist of a sequential replacement of generalist species with specialist species, which was reflected by a directional assembly at the plant trait level. Grassland isolation was found to slow down community assembly at both the species and the trait level without changing the general direction of assembly. This slowdown became less pronounced with increasing time since restoration.Spatial isolation of the restoration patches was found to act as a trait filter, independent of assembly age. We found a proportionally higher occurrence of species with light seeds and a high seed attachment potential in more isolated restoration patches, suggesting that colonization is more limited in isolated grasslands.Synthesis and applications. We demonstrate that the assembly process, at both the species and the trait level, is influenced by the position of the restoration patch in the landscape. Monitoring schemes following ecological restoration should therefore include the spatial context of the system while using both a trait‐based and a species‐based plant community analysis. Successful restoration requires physically interconnecting grassland fragments and probably the introduction of seeds or seedlings of species with low dispersability.

Individual and Temporal Variation in Outcrossing Rates and Pollen Flow Patterns in Ceiba pentandra (Malvaceae: Bombacoidea)

AbstractCeiba pentandra is a tropical tree with high rates of selfing in some populations. In mixed‐mating species, variation in selfing is due to changes in adult density or variability of incompatibility systems. The effect of spatial isolation and phenology on selfing rates and pollen flow distances was analyzed using microsatellites in a fragmented population of Ceiba pentandra, in southern Costa Rica. Adult trees within a heterogeneous landscape were classified as grouped or isolated. We compared selfing rates at the individual level, between isolation conditions and 2 yr (2007, 2009), which differed in the number of flowering individuals. Mixed mating was estimated in both years (tm = 0.624–0.759). Trees mated predominantly by outcrossing, while only a few trees reproduced through selfing. Spatial isolation did not significantly affect outcrossing rates. The progeny of grouped trees was mostly sired by near‐neighbors (<1 km) and by long‐distance pollen flow events in isolated trees. A reduction in the number of flowering individuals in 2009 reduced near‐neighbor matings, increased selfing in grouped trees, and decreased the number of unsampled sires in the progeny. Comparing selfing rates on individuals that flowered in both reproductive periods suggests a flexible mating system. Variation in self‐fertilization rates in this population appears to depend on variation of individual traits, such as genetic variability in self‐incompatibility genes, but it is independent of landscape heterogeneity. In contrast, pollen flow distances depend on local tree density as bats concentrate their foraging between near individuals to maximize energy efficiency.

The effects of habitat and spatial features of wetland fragments on the abundance of two rallid species with different degrees of habitat specialization

Capsule Water Rail Rallus aquaticus and Moorhen Gallinula chloropus abundance is affected by habitat (both species), site isolation (Water Rail) and elevation (Moorhen). Aims To evaluate the effects of patch area, habitat, isolation, elevation and inter-specific interactions on the abundance of two under-studied species, Water Rail and Moorhen; i.e. a wetland specialist and a more generalist species, respectively. Methods We modelled species' abundance at 28 sites in a wetland system in Trentino (Italy), using variables describing both habitat and spatial configuration of sites. We evaluated spatial autocorrelation and carried out an aicc -based model ranking and averaging, whose results were cross-checked using hierarchical partitioning. Results Water Rail abundance was positively affected by cover of reed-bed and other wetland herbaceous vegetation, and negatively by the distance to the nearest wetland. Moorhen abundance was positively affected by cover of reed-bed and negatively by elevation and cover of woody vegetation. Conclusions Results matched the preference for reed-beds and other wetland herbaceous vegetation reported at the local scale for Water Rails, and highlighted a negative effect of spatial isolation. Our work further demonstrates how explanations of species occurrence and abundance in fragmented landscapes must consider variables describing both habitat quality and spatial configuration.

Partitioning the effects of spatial isolation, nest habitat, and individual diet in causing assortative mating within a population of threespine stickleback.

Assortative mating is measured as a phenotypic or genotypic correlation between mates. Although biologists typically view assortative mating in terms of mate preference for similar partners, correlations between mates can also arise from phenotypic spatial structure arising from spatial isolation or habitat preferences. Here, we test whether diet-assortative mating within an ecologically variable population of threespine stickleback results from small-scale geographic isolation or microhabitat preference. We find evidence for assortative mating in the form of a positive correlation between mated pairs' diets (measured using stable isotopes). Stable isotopes reveal diet differences between different nesting areas and among individuals using different nest habitat within a nesting area. This spatial segregation of diet types should generate some assortative mating, but is insufficient to explain the observed assortment strength. Significant male-female isotope correlations remain after controlling for spatial variables. We therefore conclude that sticklebacks' diet-assortative mating arises from additional behavioral preference. More generally, our results illustrate the point that spatial segregation can only drive appreciable levels of phenotypic assortative mating when environment-phenotype correlations are parallel and strong in both sexes. Consequently, intraspecific assortative mating may typically entail mating preferences rather than just spatial cosegregation of phenotypes.

Isolamento visual ou espacial em ruminantes.

A produção animal em sistemas intensivos tem se ampliado no mundo, sempre visando à elevação de índices produtivos e retorno econômico, respectivamente. Essa verticalização da pecuária tem provocado algumas adaptações de manejo e também nas instalações, que tem alterado o comportamento dos animais, oriundo das restrições tanto visual como espacial do indivíduo. Na pecuária leiteira, a criação de bezerros em baias individuais é um exemplo dessa verticalização, tornando então uma prática comum em muitos países. Sabendo que os bovinos são animais sociais que mostram alta disponibilidade para formar vínculo social com outros indivíduos da mesma espécie, alguns órgãos têm implantado legislações para garantir um mínimo de conforto para esses animais. Um estudo sistemático das preferências sociais dos animais e os efeitos calmantes do animal companheiro de familiaridade diferente são necessários para documentar a resposta à separação. Objetivou-se com esta revisão, apresentar e discutir o efeito do isolamento espacial e/ou visual sobre as respostas produtivas e comportamentais de animais ruminantes.

Single host trees in a closed forest canopy matrix: a highly fragmented landscape?

Abstract: Whether trees represent habitat islands and therefore are influenced by similar biogeographic processes as ‘real’ islands is controversial. For trees in highly fragmented landscapes the impacts of spatial isolation on arthropod communities have already been demonstrated. However, we have almost no evidence that in large forests the arthropod communities on single trees in a closed canopy matrix are influenced by similar processes. In the present study the influence of spatial isolation on the specialized oak crown fauna was analysed in a large broadleaved forest area in northern Bavaria, Germany. The dependence of specialists on the proportion of oaks in the surrounding forest was investigated by using flight interception traps (67 on oak, 19 on beech). As target species, saproxylic and herbivorous Coleoptera and Heteroptera were sampled. The following two hypotheses were tested: (1) The proportion of oak specialists differs for oaks in beech forests and oaks in oak forests. (2) The proportion of oak specialists increases with the proportion of oaks in the surrounding forest. For all species groups, the proportion of oak specialists was higher in oak crowns than in beech crowns. Herbivorous beetles and true bugs showed a higher proportion of specialists in oak forests than on single oaks in beech forests. The proportion of herbivorous oak specialists increased significantly with increasing numbers of adjacent oak trees, while saproxylic Coleoptera showed no relationship to oak density. For herbivorous Coleoptera a threshold of higher proportion occurred where >30% oak was present, and for Heteroptera a first threshold was identified at values >70% and a second at >30%. This indicates that larger habitat patches within a closed forest canopy matrix support larger populations of herbivorous oak specialists. Hence, similar effects of spatial isolation might occur in a closed forest as have already been shown for highly fragmented open landscapes.

Distribution of aquatic plants in the Northern Vosges rivers: implications for biomonitoring and conservation

1. The continual confusion over the definition of the term ‘trophic status’ has led to ambiguous demonstrations of the influence of alkalinity versus inorganic N and P on aquatic plant distribution. 2. Data from the Northern Vosges rivers (sandstone geology) were reinvestigated to test whether it was possible to separate the effect of (i) spatial isolation from surface water chemistry, and (ii) alkalinity from inorganic N and P on aquatic macrophyte distribution. 3. Alkalinity and pH exerted the strongest influence on plant distribution, soluble reactive phosphorus (SRP) and pCO2 being subordinate. The effect of spatial isolation between catchments was not significant, which may indicate that aquatic plants dispersed well over the area. The effect of longitudinal connectivity on species distribution was strong, although largely confounded by the effects of water chemistry and possibly other physical factors not recorded. The partial effect of SRP (after removing the effect of pH or alkalinity) was still significant. However this was not the case for NH4. 4. The floristic composition was more likely to indicate the role played by alkalinity than inorganic P, with inorganic N being further subordinate. However, the causality of the significant relationships needs to be investigated further. This study questioned the validity of current macrophyte biomonitoring tools striving to indicate the concentrations of inorganic N and P. 5. More work is needed to quantify the role of connected and isolated aquatic habitats in the region, in order to understand how to maintain the species pool and to ensure that recolonization rates compensate for the losses due to disturbances. It is not clear how the vegetation would respond to inorganic P enrichment (or control), based on the individual species response observed here, and river P uptake studies from other rivers. Future monitoring should also include measurements of physical degradation. Copyright © 2007 John Wiley & Sons, Ltd.

Microarthropod density and diversity respond little to spatial isolation

Summary The effect of spatial isolation on the soil microarthropod community of a deciduous forest was investigated for 16 months. Soil animals were confined in plastic tubes (diameter: 7 cm; length: 15 cm). We expected the density and diversity of most microarthropods to decrease with time in isolated habitats and this decline to be more pronounced in species of high trophic level. We also expected that species that are top-down controlled, such as collembolans, would benefit from reduced predator densities whereas species suffering little from enemies, such as oribatid mites, would be little affected. In contrast to these hypotheses, the density and diversity of almost all microarthropod taxa (Gamasina, most groups of Oribatida and Collembola) were not significantly reduced by isolation. Also in contrast to our expectation, the density of predators (Gamasina) increased in isolated habitats. This increase may have resulted from the release of predator pressure, due to the exclusion of macrofauna predators. We conclude that soil microarthropods in the studied forest are insensitive to spatial isolation. Food generalism and parthenogenetic reproduction may enable them to persist in isolated communities.

A two-species test of the hypothesis that spatial isolation influences microbial diversity in soil.

The hypothesis that spatial isolation is a key determinant of microbial community structure in soils was evaluated by examining the competitive dynamics of two species growing on a single resource in a uniform sand matrix under varied moisture content. One species dominated the community under highly connected, saturated treatments, suggesting that these conditions allow competitive interactions to structure the community. As moisture content decreased, however, the less competitive species became established in the community. This effect was most pronounced at a matric water potential of -0.14 MPa where estimates of final population density and species fitness were equal. A second but more closely related species pair exhibited a similar response to decreasing moisture, suggesting that the effects of spatial isolation we observed are not simply a species-pair-specific phenomenon. These findings indicate that spatial isolation, created by low moisture content, plays an important role in structuring soil microbial communities.

Molecular variability of geographically distinct isolates of Rice yellow mottle virus in Africa.

The coat protein gene (ORF4) and the 3' untranslated region of a sample of 40 isolates of Rice yellow mottle virus (RYMV), 32 from West Africa and 8 from East Africa, have been sequenced. Five major strains were differentiated, three from West Africa (S1, S2, S3) and two from East Africa (S4, S5), with a spatial overlap of the strains within each of these two regions. Nucleotide and amino-acid divergence between strains was up to 11%. Although more isolates from West African were sequenced, variability was twofold lower than among East African isolates. Variability in ORF4 and in ORF2 coincided. Within strain and within isolate variations in nucleotide sequences were low. Bipartite nuclear targeting motif, Ca2+ binding sites and at least two stretches of amino-acids were conserved among the 40 RYMV isolates and the other sobemoviruses. Variants associating sequence motifs characteristic of different strains have been found, possibly resulting from recombination events. Differences in pathogenicity among isolates were associated with changes of amino-acids in the bipartite nuclear targeting motif of the R domain of the capsid protein, and around conserved positions 151-154 of the S domain. We hypothesise that the observed pattern of variation of RYMV reflects the effect of spatial isolation between East and West Africa coupled with adaptive changes associated to the original virus reservoirs of the different strains.

In defence of small habitat islands: Termites (Isoptera) in the Western Australian central wheatbelt, and the importance of dispersal power in species occurrence

Ecological theory has long undervalued the contribution of small remnants of native vegetation to nature conservation. This study provides data on colony persistence of remnant-dependent wood-eating termites in 28 remnants of mature wandoo (Eucalyptus capillosa) trees in paddock situations in the agricultural south-west of Western Australia. Remnants ranged in size from 2 to 30 trees, and in spatial isolation from 50 to 650 m. All remnants have been exposed to livestockrelated disturbance for >40 years. This study found that (1) Small remnants of eucalypt trees on farms retain important functional representatives, i.e., wood-eating termites for nutrient-cycling, and high species numbers. (2) Seventeen species have the capacity to establish and maintain colonies in remnants =5 trees. (3) Spatial isolation has no significant influence on the total number of termite species. (4) The number of trees (r = 0.60) and quantity of dead wood in the remnant (r = 0.86) were significant indicators of total termite species number. Larger remnants with low quantities of wood supported few termites, however. (5) Rare as well as common species persisted in small remnants. (6) Alate wing-size was a significant indicator of the occurrence of the six most common termite species in remnants (r = 0.84). The implication of isolation effects for rare species with limited powers of dispersal is self-evident, as is the need for the creation of habitat linkeages to reduce the effects of spatial isolation on the native fauna.

Effects of Isolation on the Occurrence of a Fungivorous Forest Beetle, Bolitotherus cornutus, at Different Spatial Scales in Fragmented and Continuous Forests

We investigated the effect of spatial isolation on the incidence of a fungivorous forest beetle in continuous and fragmented forests at three spatial scales, while controlling for confounding variables, such as patch size and quality. Isolation was measured using nearest-neighbour distances and we compared the usefulness of measuring multiple patches and considering either occupied or unoccupied patches. An effect of spatial isolation on beetle incidence was evident at all three scales: between fungal carps on a log (0 to 2 m), between carp clusters in a forest (1 to 71 m) and between woodlots in an agricultural matrix (25 to 2000 m). The magnitude of the isolation effect was stronger at the largest scale than at the smallest scale. However, isolation was most prevalent (i.e. significant for all measures of isolation) at the intermediate scale. The effect of isolation was not influenced by forest configuration type (continuous or fragmented) or by patch density, but there was a marginal compensatory effect of patch size on isolation. Isolation measures incorporating only occupied patches were not generally better predictors than isolation measures incorporating all patches. Little information would have been lost by using only the distance to the closest patch to measure isolation effects, rather than incorporating distances to multiple patches.

Pollen dispersal and representation on an offshore island.

The effects of spatial isolation on pollen representation were examined in a study of seven small kettle ponds on Block Island, a small, unforested island 19 km off the New England Coast (USA). Modern pollen assemblages from the ponds were compared with modern assemblages from similar ponds on the adjacent, partly forested mainland and in extensively forested northern New York. Representation of pollen from local and extralocal sources was amplified on the island owing to spatial isolation. However, variation among pollen assemblages on the island was not clearly related to spatial variation in vegetation composition. Significant transport of pollen from the mainland to the island was observed. There appeared to be little or no decrease in representation of large, poorly dispersed mainland pollen types between the mainland and island. This latter result may indicate differences between the mainland and island in the predominant modes of pollen transport, or alternatively, effects of local pollen source strength on representation of pollen from distant sources. Based on our results, we propose a theory of pollen representation on islands that can be tested and applied on offshore islands and patchy landscapes.