Ecosystems effects 25 years after Chernobyl: pollinators, fruit set and recruitment

Animals are assumed to play a key role in ecosystem functioning through their effects on seed set, seed consumption, seed dispersal, and maintenance of plant communities. However, there are no studies investigating the consequences of animal scarcity on seed set, seed consumption and seed dispersal at large geographical scales. We exploited the unprecedented scarcity of pollinating bumblebees and butterflies in the vicinity of Chernobyl, Ukraine, linked to the effects of radiation on pollinator abundance, to test for effects of pollinator abundance on the ecosystem. There were considerably fewer pollinating insects in areas with high levels of radiation. Fruit trees and bushes (apple Malus domestica, pear Pyrus communis, rowan Sorbus aucuparia, wild rose Rosa rugosa, twistingwood Viburnum lantana, and European cranberry bush Viburnum opulus) that are all pollinated by insects produced fewer fruit in highly radioactively contaminated areas, partly linked to the local reduction in abundance of pollinators. This was the case even when controlling for the fact that fruit trees were generally smaller in more contaminated areas. Fruit-eating birds like thrushes and warblers that are known seed dispersers were less numerous in areas with lower fruit abundance, even after controlling for the effects of radiation, providing a direct link between radiation, pollinator abundance, fruit abundance and abundance of frugivores. Given that the Chernobyl disaster happened 25 years ago, one would predict reduced local recruitment of fruit trees if fruit set has been persistently depressed during that period; indeed, local recruitment was negatively related to the level of radiation and positively to the local level of fruit set. The patterns at the level of trees were replicated at the level of villages across the study site. This study provides the first large-scale study of the effects of a suppressed pollinator community on ecosystem functioning.     

Migration, coherence and persistence in a fragmented landscape

The chance of local extinction is high during periods of small population size. Accordingly, a metapopulation made of local communities that support internal population cycling may face the threat of regional extinction if the local dynamics is coherent (synchronized). These systems achieve maximum sustainability at an intermediate level of migration that allows recolonization but prevents synchronization. Here we implement an individual-based simulation technique to examine the maximum persistence condition for a system of patch habitats connected by passive migration. The models discussed in this paper take into consideration realistic elements of metapopulations, such as migration cost, disordered spatial structure, frustration and environmental noise. It turns out that the state with maximum anti-correlation between neighboring patches is the most sustainable one, even in the presence of these complications. The results suggest, at least for small systems, a model independent conservation strategy: coherence between neighboring local communities has, in general, a negative impact, and population will benefit from intervention that increases anti-correlations.     

Endogenous polyamines in apple and their relationship to fruit set and fruit growth

The distribution of free and bound polyamines was investigated from blooming until harvest on flower, fruitlets and fruits of Malus domestica Borkh cv. Golden Delicious, Relationships between polyamines and fruit set and growth were also investigated. The level of free polyamines was high only during the first weeks after full bloom and then decreased gradually. The amount of bound trichloroacetic acid-insoluble polyamines was much higher than free polyamines. Bound spermine in particular showed a high value for almost 40 days after full bloom, while spermidine and putrescine were no longer detectable even a few days after full bloom.
In relation to fruit set, it was possible to observe that abscission peaks took place when free polyamine levels were low or decreasing. Insofar as fruit growth is concerned, the most substantial variations in polyamine levels occurred very early in the season when fruit dry weight and protein amount were also changing rapidly and fruit diameter was almost impossible to measure.     

Host-parasitoid extinction and colonization in a fragmented prairie landscape

Few field studies of natural populations have examined the factors influencing local extinctions and colonization of empty habitat patches for a prey species and its predator. In this study, I carried out a census of planthopper (Prokelisia crocea; Hemiptera: Delphacidae) and egg parasitoid (Anagrus columbi; Hymenoptera: Mymaridae) incidence and densities in 147 host-plant patches (Spartina pectinata; Poaceae) over seven planthopper generations in a tall-grass prairie landscape. For both species, the likelihood of going extinct in a patch was related to a number of patch-specific variables: density, temporal variability in density, proportion of hosts parasitized (planthopper only), host-plant density, patch size, patch isolation, and composition of the surrounding matrix. Colonization likelihood was related only to the physical attributes of the patch. There was high patch turnover in this prairie landscape. On average, planthoppers went extinct in 23% of the patches and A. columbi went extinct in 51% of the patches in each generation. For the planthopper, extinction likelihood increased with a decrease in patch size and the proportion of the matrix composed of mudflat. Parasitism of eggs had no effect on the extinction likelihood of local P. crocea populations, suggesting that A. columbi may not play a major role in the patch dynamics of its host. The likelihood of extinction for A. columbi was dependent on factors that spanned three trophic levels. An increase in plant density, decrease in host density and decrease in parasitoid density all increased the likelihood of A. columbi extinction within a patch. The dependency on multiple trophic levels may explain the higher extinction risk for the parasitoid than its host. A. columbi extinction was also affected by the matrix habitat surrounding the patch—the effect was the opposite of that for P. crocea. Finally, vacant patches were colonized at rates of 53% and 34% per generation for the planthopper and parasitoid, respectively. For both species, colonization probabilities decreased with an increase in patch isolation. High host densities in a patch also favored high rates of colonization by A. columbi. I discuss how anthropogenic changes to the prairie landscape can affect the metapopulation dynamics and persistence time of this host-parasitoid interaction.     

Pollination in Jacaranda rugosa (Bignoniaceae): euglossine pollinators, nectar robbers and low fruit set

Nectar robbers access floral nectar in illegitimate flower visits without, in general, performing a pollination service. Nevertheless, their effect on fruit set can be indirectly positive if the nectar removal causes an incremental increase in the frequency of legitimate flower visits of effective pollinators, especially in obligate outcrossers. We studied pollination and the effect of nectar robbers on the reproductive fitness of Jacaranda rugosa , an endemic shrub of the National Park of Catimbau, in the Caatinga of Pernambuco, Brazil. Xenogamous J . rugosa flowers continuously produced nectar during the day at a rate of 1 μl·h⁻¹. Female and male Euglossa melanotricha were the main pollinators. Early morning flower visits substantially contributed to fruit set because stigmas with open lobes were almost absent in the afternoon. Ninety-nine per cent of the flowers showed damage caused by nectar robbers. Artificial addition of sugar water prolonged the duration of flower visits of legitimate flower visitors. Removal of nectar, simulating the impact of nectar robbers, resulted in shorter flower visits of euglossine bees. While flower visits of nectar-robbing carpenter bees ( Xylocopa frontalis , X . grisescens, X . ordinaria) produced only a longitudinal slit in the corolla tube in the region of the nectar chamber, worker bees of Trigona spinipes damaged the gynoecium in 92% of the flowers. This explains the outstandingly low fruit set (1.5%) of J. rugosa in the National Park of Catimbau.     

Recruitment limitations in Primula vulgaris in a fragmented landscape

Plant recruitment is limited by dispersal, if seeds cannot arrive at potential recruitment sites, and by establishment, due to a low availability of safe sites for recruitment. Seed-sowing experiments, scarcely applied along gradients of landscape alteration, are very useful to assess these limitations. Habitat loss and fragmentation may foster recruitment limitations by affecting all the processes from seed dispersal to seedling establishment. In this study, we perform a seed-sowing experiment to disentangle the importance of dispersal and establishment limitations in different stages of recruitment of the perennial herb Primula vulgaris in fragmented forests of the Cantabrian Range (Northwestern Spain). We evaluated the influence of ecological gradients resulting from habitat loss and fragmentation (modifications of habitat amount at the landscape and microhabitat scales, changes in the species’ population size, changes in seed predation and seedling herbivory) on seedling emergence, survival and early growth. We found strong evidence of dispersal limitation, as seedling emergence was very low in experimental replicates where no seeds were added. This limitation was independent of landscape alterations, as we found no relation with any of the ecological gradients studied. Establishment limitations at the germination phase were also unrelated to ecological gradients, probably because these limitations are more related to fine-scale environmental gradients. However, further monitoring revealed that seedling survival after summer and winter periods and seedling growth were conditioned by landscape alteration, as we found effects of habitat amount at the landscape and microhabitat scales, of presence of populations of P. vulgaris and of seedling herbivory. These effects were complex and sometimes opposite to what can be expected for adult plants, revealing the presence of different requirements between life stages.     

A land snail's view of a fragmented landscape

Habitat fragmentation may influence the genetic structure of populations, especially of species with low mobility. So far, these effects have been mainly studied by surveying neutral markers, and much less by looking at ecologically relevant characters. Therefore, we aimed to explore eventual patterns of covariation between population structuring in neutral markers and variation in shell morphometrics in the forest‐associated snail Discus rotundatus in relation to habitat fragment characteristics. To this end, we screened shell morphometric variability and sequence variation in a fragment of the mitochondrial 16S rDNA gene in D. rotundatus from the fragmented landscape of the Lower Rhine Embayment, Germany. The 16S rDNA of D. rotundatus was highly variable, with a total of 118 haplotypes (384 individuals) forming four clades and one unresolved group. There was a geographic pattern in the distribution of the clades with the river Rhine apparently separating two groups. Yet, at the geographic scale considered, there was no obvious effect of fragmentation on shell morphometrics and 16S rDNA variation because G_ST often was as high within, as between forests. Instead, the age of the habitat and (re‐)afforestation events appeared to affect shell shape and 16S rDNA in terms of the number of clades per site. The ecologically relevant characters thus supported the presumably neutral mitochondrial DNA markers by indicating that populations of not strictly stenecious species may be (relatively) stable in fragments. However, afforestation after large clearcuts and habitat gain after the amendment of deforestation are accompanied by several, seemingly persistent peculiarities, such as altered genetic composition and shell characters (e.g. aperture size). © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 98 , 839–850.     

Habitat use by beech martens in a fragmented landscape

We investigated key habitat features used by beech martens occupying a fragmented agricultural landscape. Locations of eight martens were radio-monitored daily for 4–12 months each. We evaluated the selection of home ranges within a geographic area, as well as the selection of habitat features within home ranges, using random simulations for comparison. Home ranges included more wood and scrub vegetation, and less arable land, than random simulations. They also included a higher proportion of watercourses with continuous vegetation along their verges, and were closer to these watercourses than random simulations. Within home ranges, beech martens used wood and scrub vegetation, and farm buildings, more intensively than expected, and arable land less than expected. On average, beech martens stayed close to watercourses (where most of the wood vegetation occurred) but not to farm buildings, indicating that only the former shaped beech marten movements. By these findings, arable land appeared to act as a seldom traversed barrier, making farm buildings uneasy to reach if they are located far from watercourses.     

Roe deer population structure in a highly fragmented landscape

Northern Belgium (Flanders) is one of the most densely populated and urbanized regions in Europe. Many species are therefore likely to suffer from anthropogenic pressure and habitat destruction and fragmentation. Although many large mammals are recolonizing in parts of Europe, including Belgium, due to adaptation, a relaxation of persecution and habitat restoration, we have little actual data concerning the effects of landscape features on their population structure. We analysed the genetic structure of discrete roe deer (Capreolus capreolus) populations in the Eastern part of Flanders, with special emphasis on the impact of habitat fragmentation and anthropogenic barriers. The sampled populations were clearly genetically differentiated. Genetic structure could be explained by purely distance-based landscape modelling, but a simpler model focusing solely on barrier effects of large transportation infrastructure explained nearly as much genetic variance. In contrast, analyses based on least-cost landscape modelling failed to yield a significant effect. Overall, the results suggest considerable landscape-level effects of transportation infrastructure.     

Population genetics of orchid bees in a fragmented tropical landscape

The prospects for persistence of bees living in fragmented landscapes is a topic of considerable interest due to bees’ importance as pollinators of agricultural crops and wild plants, coupled with the ubiquity of native habitat loss and evidence that bees may be declining worldwide. Population persistence in fragmented areas depends on dispersal potential and maintenance of gene flow among fragments of habitat. Here we used population genetic techniques to characterize, for two equally abundant orchid bee species that differ in their physiology and ecology, levels of genetic differentiation among fragments of tropical forest in southeastern Costa Rica in a ~200 km² landscape. We measured population differentiation with ϕ_PT (an analogue to the traditional summary statistic Fst), as well as two measures that may more accurately reflect the level of differentiation when highly variable loci are used: G’st and D_est. We also calculated pairwise genetic distances among individuals and conducted Mantel tests to test the correlation of genetic and geographic distance, for each species. We found strong differences in genetic structure between the species. Contrary to our expectations, each measure of genetic structure revealed that the larger-bodied species, Eulaema bombiformis, had higher levels of differentiation than the smaller species, Euglossa championi. Furthermore, for Eulaema bombiformis there was a significant positive correlation of genetic and geographic distance while for Euglossa championi there was no significant positive correlation. Our results demonstrate that bee species can have strikingly different levels of gene flow in fragmented habitats, and that body size may not always act as a useful proxy for dispersal, even in closely related taxa.     

Mermithid parasitism of Hawaiian Tetragnatha spiders in a fragmented landscape

Hawaiian Tetragnatha spiders inhabiting small forest fragments on the Big Island of Hawaii are parasitized by mermithid nematodes. This is the first report of mermithid nematodes infecting spiders in Hawaii, and an initial attempt to characterize this host-parasite interaction. Because immature mermithids were not morphologically identifiable, a molecular identification was performed. A phylogenetic analysis based on 18S small ribosomal subunit nuclear gene sequences suggested that Hawaiian spider mermithids are more closely related to a mainland presumptive Aranimemis species that infects spiders, than to an insect-infecting mermithid collected on Oahu, HI, or to Mermis nigrescens, also a parasite of insects. Measured infection prevalence was low (ranging from 0 to 4%) but differed significantly among forest fragments. Infection prevalence was associated significantly with fragment area, but not with spider density nor spider species richness. Results suggest that mermithid populations are sensitive to habitat fragmentation, but that changes in infection prevalence do not appear to affect spider community structure.     

Bee diversity in a fragmented landscape of the Mexican neotropic

The effects of fragmentation on tropical bee communities are not well understood. The present study investigated these effects on wild bee species richness and diversity in fragments of tropical forest in the Yucatan Estate (Mexico). We present an analysis of bee community structure based on fragment size, connectivity, and bee life form, and include an analysis of m-dominance to evaluate if large fragments sustain greater species diversity compared to small fragments. Results indicated that the bee community within each fragment was composed of different bee species, and that species richness and diversity increased with fragment size, although this relationship varied between the life forms. Results suggest a high degree of isolation between fragments and greater differences in species composition. The m-dominance analysis indicated that 37% of the species recorded were restricted to medium and large-size fragments, while all other species were randomly distributed across fragments of different size in general; ours results indicate that not only do large fragments support greater species diversity than small fragments, but they are also essential for the conservation of wild bee species.     

GPS measurement error and resource selection functions in a fragmented landscape

Advances in technology have allowed ecologists to employ remote observations of individual organism's spatial location. These data are used to model species distributions and habitat associations, which inform conservation efforts and management plans. These data are not without error. To illustrate the consequences of not considering measurement error, I introduce measurement error to a habitat selection model, using three different distributions. I show how measurement error can confound inferences made about a hypothetical organism's true habitat selection. By simulating different initial strengths of selection I show the introduction of measurement error results in the largest reduction in habitat selection strength (from truth) for very selective individuals (habitat specialists). Not surprisingly, the inclusion of error in very weakly selective individuals (habitat generalists) can result in a switching from true selection to observed avoidance. Researchers need to be aware that, first, there is measurement error in remotely observed data, and second, a tradeoff occurs between measurement error and landscape fragmentation. Landscapes with a high degree of fragmentation require spatially accurate (low measurement error) data in order to make reliable estimates of habitat selection or species distribution. The results of this study are discussed in light of the conservation of species threatened by habitat fragmentation and the management suggestions arising from selection studies.     

Richness and abundance of stream fish communities in a fragmented neotropical landscape

Environmental Biology of Fishes - Environmental conditions influence ecological processes that shape stream community diversity and abundance. Deforestation has the potential to limit available...     

Experimental evidence for edge-related predation in a fragmented agricultural landscape

Abstract This study tested the hypothesis that increased predation of experimental nests occurs close to a forest edge in a fragmented agricultural landscape. Artificial nests and eggs of willie wagtails Rhipidura leucophrys and superb fairy-wrens Malurus cyaneus were used in experiments to assess the extent and nature of predation occurring throughout the known breeding seasons of these species. Predators were identified by the imprints they left in plasticine eggs, and by remote photography. Surveys of avian predators were undertaken to investigate the relationship between predation intensity and predator distribution and abundance. Avian predators accounted for almost all predation for which a predator could be identified (96%). Five of seven predator species photographed attacking wagtail nests were corvids or artamids. Fairy-wren nests suffered relatively low rates of predation (29%) compared to wagtail nests (87%). Increased predation at the habitat edge was recorded for wagtail nests only; predation was correlated with the distribution and abundance of predatory avian species. The different extent and pattern of predation on fairy-wren nests could be explained by problems in detecting predation by mammals, and by possible failure of avian predators to locate the cryptic nests.     

Changes in carabid beetle diversity within a fragmented agricultural landscape

The distribution of carabid and cicindelid (Coleoptera: Carabidae) beetles in five distinct habitats (riparian, mature orchard, pine windbreak, young orchard, natural veld), within Tambuti Citrus Estate (Swaziland) was examined by pitfall trapping over 18 months. Habitats with high vegetation and litter cover had the highest species diversity and larger specimens, e.g. riparian border and pine windbreak, while the lowest diversity was observed in intensively managed mature citrus orchards. While species such as Tefflus delagorguei Guérin occurred in all the habitats sampled, certain species illustrated habitat specificity; e.g. Dromica ambitiosa Péringuey was observed only in the pine windbreaks while Haplotrachelus sp. Chaudoir occurred mainly in the vegetated riparian and natural veld habitats. Four unidentified carabid beetles were exclusive to the riparian border habitat. This habitat was the only one with a distinct assemblage of species in the agricultural mosaic studied. Multivariate analyses were used to assess the role of soil and environmental variables in relation to the ground beetle diversity within the agricultural mosaic studied.     

The frequency of metapopulations, metacommunities and nestedness in a fragmented landscape

Metapopulation and metacommunity theory may be extremely useful for understanding community composition and species distributions in fragmented landscapes. However, how well particular spatial ecological models represent natural systems is not known and so the general importance of those models is unclear. In three naturally fragmented landscapes in Tasmania, Australia, I sampled beetles from 67 sites, including continuous forest, small forest patches in a sedgeland matrix, streamside forest, and the matrix. Of forty commonly captured beetle species, at least 37% do not form metapopulations of any kind because they do not disperse far enough, disperse too far, or occur in the matrix. Only 7.5% of the species showed distributions consistent with a mainland‐island metapopulation, which was surprising given the mainland‐island structure of the landscape. These patterns were also consistent with a classic metapopulation. Deterministic metapopulations were probably common, involving at least 32% of species. Most predicted metacommunity patterns were not observed because only subsets of the fauna followed a particular metacommunity model. Seven, mostly flying, species were influenced only by habitat quality, supporting the Species‐sorting or Mass‐effects models, and the strong distinction between the beetle fauna of Eucalyptus patches and the matrix suggested an over‐riding influence of a Species‐sorting process. Seven, mostly flightless, species showed a negative relationship with increasing patch isolation, while another six, mostly flying, species showed the opposite pattern, with higher frequency of occurrence in more isolated patches. Both groups were strongly nested. The flying species were probably excluded from less isolated sites through interactions with poor dispersers , providing a novel mechanism leading to a nested distribution. The Patch‐dynamics and Species‐sorting processes were equally consistent with the pattern, emphasizing that these models are relatively simplistic when confronted with real community data. Additional complexity needs to be built into the models to accommodate the diverse patterns observed in natural communities.