Species responses of colonising beetles to variation in patch quality,number, and context in experimental aquatic landscapes

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Habitat quality and population density drive occupancy dynamics of snowshoe hare in variegated landscapes

The influence of habitat quality and population density on occupancy dynamics may surpass that of traditional metrics of area and isolation, but often this is not considered explicitly in studies of spatially structured populations. In landscapes that are not easily characterized as binary habitat/non‐habitat (e.g. variegated landscapes), this influence may be even more important and occur at both local and landscape levels. It follows that occupancy dynamics may be driven by disparate processes depending on how extinction or colonization relate to habitat quality and population density. We examined the relative influence of area, structural isolation, habitat quality, local population density, and neighborhood population density (i.e. population density in the landscape around a site) on the probability of extinction and colonization of snowshoe hare Lepus americanus across an expansive forest mosaic landscape (encompassing the northern third of Idaho). Habitat quality and population density were highly influential in determining extinction and colonization, whereas patch area and isolation were much less important. Sites with heavier vegetative cover at the site or landscape‐level were more likely to be colonized and less likely to go extinct, and sites with greater local population density in the previous time step had lower probability of extinction. Sites embedded in high density neighborhoods also were less likely to go extinct, but not more likely to be colonized. We found a significant interaction between local and neighborhood population density on extinction in 1 yr, suggesting that the strength of demographic rescue may vary dependent on local site densities. Our results add to a growing literature showing that factors outside of structural metrics of area and isolation are important drivers of occupancy dynamics. Given the multi‐scaled influence of habitat quality and population density on occupancy dynamics, our work also indicates that research on snowshoe hare must extend beyond simply assessing local factors to understand the spatial dynamics of populations.     

Root quality and decomposition environment,but not tree species richness,drive root decomposition in tropical forests

Plant and Soil - Tropical forests contribute significantly to the global carbon cycle, yet the relative importance of tree diversity on key ecosystem processes such as root decomposition remains...     

Premating, not postmating, barriers drive genetic dynamics in experimental hybrid populations of the endangered Sonoran topminnow

The timing and pattern of reproductive barrier formation in allopatric populations has received much less attention than the accumulation of reproductive barriers in sympatry. The theory of allopatric speciation suggests that reproductive barriers evolve simply as by-products of overall genetic divergence. However, observations of enhanced premating barriers in allopatric populations suggest that sexual selection driven by intraspecific competition for mates may enhance species-specific signals and accelerate the speciation process. In a previous series of laboratory trials, we examined the strength of premating and postmating barriers in an allopatric species pair of the endangered Sonoran topminnow, Poeciliopsis occidentalis and P. sonoriensis. Behavioral observations provided evidence of asymmetrical assortative mating, while reduced brood sizes and male-biased F(1) sex ratios suggest postmating incompatibilities. Here we examine the combined effects of premating and postmating barriers on the genetic makeup of mixed populations, using cytonuclear genotype frequencies of first- and second-generation offspring. Observed genotype frequencies strongly reflect the directional assortative mating observed in behavioral trials, illustrating how isolating barriers that act earlier in the reproductive cycle will have a greater effect on total reproductive isolation and may be more important to speciation than subsequent postmating reproductive barriers.     

Patch quality and connectivity influence spatial dynamics in a dune wolfspider

The spatial population dynamics of the wolfspider Pardosa monticola, inhabiting patchily distributed grasslands in the Flemish coastal dunes of Belgium and Northern France were investigated with incidence function models using field survey data from 1998 and 2000. Vegetation height and patch size were related to habitat quality. Mark-recapture experiments revealed maximum cursorial dispersal distances of 280 m for moss dunes and 185 m for higher dune grassland. Higher shrub vegetation appeared to be dispersal barriers. These habitat-dependant cursorial distances and the theoretically estimated ballooning distance were included with patch distances into a connectivity index for both dispersal modes. Forward multiple regression indicated that patch occurrence was influenced by habitat quality and ballooning connectivity. Habitat quality and cursorial connectivity explained patterns in short-term colonisation. Extinction appeared to be stochastic and not related to habitat quality and connectivity. Genetic differentiation and variability was low. The discrepancy between the estimated low dispersal capacity and the indirect estimate of gene flow ( F(ST)) indicates that historical population dynamics and/or historical ballooning dispersal influence the genetic structure in this species.     

Warming water and leaf litter quality but not plant origin drive decomposition and fungal diversity in an experiment

The fungi associated with leaf litter play a key role in decomposition and can be affected both by the warming water and the invasion of non-native species in riparian vegetation. Warming water and invasion of non-native riparian species on stream fungal communities have been studied mainly in temperate ecosystems. We tested the effects of warming water and non-native plant Psidium guajava on leaf litter decomposition, conidia density, species richness and beta diversity of tropical stream fungi. Thus, we carried out an experiment using the current mean temperature of streams from northwestern Paraná in South Brazil (22 °C) and two temperatures above the current mean temperature (26 °C and 29 °C). We also used the leaves of a non-native plant (P. guajava), and two native plants (one of similar nutritional quality, and the other of higher nutritional quality than the non-native species) occurring in Neotropical streams riparian vegetation. Warming water accelerated leaf litter decomposition and reduced conidia density and fungal richness in native and non-native plants. However, species composition and beta diversity were not affected by water temperature. Our study showed that warming affects the fungi of streams, the main microorganisms responsible for decomposition and that the nutritional quality of the leaves may be more important than the origin of riparian plant species. Despite this, further investigations should be conducted on the interaction of P. guajava with the flow of nutrients in these environments and how it can affect other ecosystem processes and the food chain. Efforts to study the effects of water warming and biological invasion on the attributes and distribution of fungi in streams are vital, making them a tool for the conservation of riparian ecosystems.     

When one is not necessarily a lonely number: initial colonization dynamics of Adelges tsugae on eastern hemlock, Tsuga canadensis

The ability to establish successfully in a new area can vary considerably among species. In addition to the well-recognized importance of propagule pressure in driving the rates of establishment of biological invaders, the life history strategy of a species can also affect establishment success, such as in the extent to which Allee effects (positive density-dependence), and environmental and demographic stochasticity manifest themselves. We quantified the establishment success of Adelges tsugae, a non-native insect currently invading North American hemlock. We inoculated eastern hemlock host trees with varying densities of this parthenogenetic insect, from 1 to >500 progrediens ovisacs. The number of settled sistens (the subsequent generation) was positively related to the initial density. More interesting, however, was that we recorded successful establishment from released progrediens ovisacs, and the subsequent initiation of the next generation (sistens), in ≈39 % of host trees inoculated with 1 ovisac. The observation that successful establishment can be accomplished by a single ovisac produced by a single individual has important implications in the invasion dynamics and management of A. tsugae.     

Community dominance patterns, not colonizer genetic diversity, drive colonization success in a test using grassland species

Successful colonization and/or invasion depend on characteristics of the invaded community and of the colonizer itself. Although many studies have documented a negative relationship between invasibility and biodiversity, the importance of community evenness is rarely examined and thus poorly understood. However, colonizer characteristics, including population genetic diversity, can also be important determinants of colonization success. We conducted a greenhouse experiment to assess the relative importance of community evenness and colonizer population genetic diversity using the weed Arabidopsis thaliana. We added seeds of A. thaliana (varying genetic diversity while keeping propagule pressure constant) to four types of constructed plant communities: those dominated by legumes, grasses or forbs, or with equal abundances of all three functional groups. We selected community members from a large pool of species to avoid the confounding effects of species identity. We also assessed the success of multiple seedbank colonizers to assess generality in the effects of our evenness treatments. Equal-abundance communities were no better at suppressing colonization than communities dominated by a single functional group. Forb-dominated communities suppressed A. thaliana colonization better than grass-dominated communities and suppressed seedbank colonizers better than legume-dominated communities. Equal-abundance communities were similar to forb-dominated ones in their eventual composition and in their invasibility, suggesting that forbs drove colonizer suppression in that treatment rather than high evenness itself. Most of our forbs grew quickly, yielding productive forb-dominated communities; this points to the importance of growth and colonization phenology in our system. A. thaliana genetic diversity did not affect colonization success, perhaps because strong interspecific competition substantially limited A. thaliana seedling emergence.     

Rice flooding negatively impacts root branching and arbuscular mycorrhizal colonization,but not fungal viability

Rice is mostly cultivated in wetlands, where arbuscular mycorrhization (AM) is reported to decrease. The mechanisms regulating such events are largely unknown. Rice uninoculated and inoculated with Rhizophagus irregularis were grown in dry and flooded conditions, allowing also for the transfer of plants from one water regime to the other. Roots were sampled at different times, from 7 to 35 d post‐inoculation (dpi). The morphological and molecular parameters (root branching, aerenchyma formation, mycorrhizal colonization, AM marker gene expression) were evaluated. Root branching was more pronounced in dry conditions, and such phenotype was enhanced by the fungus. In wetlands, the colonization level was comparable till 21 dpi, when the mycorrhization then decreased, paralleled by an increase in aerenchyma. Expression of the fungal transporters was comparable under the two conditions. The root apparatus, when shifted from one water regime to the other, rapidly adapted to the new condition, revealing a marked plasticity. The reversibility of the AM rice symbiosis was also mirrored by expression changes of plant marker genes. The results demonstrate that the water regime is the driving force that regulates AM colonization under flooding conditions, by directly influencing root architecture and anatomy, but without impacting the basic AM functionality.     

Interacting effects of landscape context and habitat quality on flower visiting insects in agricultural landscapes

Landscape context and habitat quality may have pronounced effects on the diversity of flower visiting insects. We investigated whether the effects of landscape context and habitat quality on flower visiting insects interact in agricultural landscapes in the Netherlands. Landscape context was expressed as the area of semi-natural habitats or the density of linear landscape features, and was quantified at spatial scales ranging from 250 to 2000 m. Habitat quality was determined as flower abundance. Species richness and abundance of hoverflies and bees were determined along 16 stream banks experiencing similar environmental conditions but situated in areas with contrasting landscape context. Only flower abundance and the area of semi-natural habitats within 500–1000 m were significantly related to species richness of hoverflies and bees and these factors had interacting effects on both species groups. Our results suggest that the regional area of semi-natural habitats had a positive effect on hoverfly species richness when flower abundance was relatively high, but not when flower abundance was low. Moreover, flower abundance had positive effects on hoverfly species richness only in areas with relatively many semi-natural habitats. Contrastingly, flower abundance had a more positive effect on bee species richness in landscapes with few semi-natural habitats compared to landscapes with more semi-natural habitats. Our results suggest that the importance of landscape context for the species richness of flower visiting insects depends upon the quality of the habitat patches.     

Environment,but not migration rate,influences extinction risk in experimental metapopulations

Ecological theory suggests that several demographic factors influence metapopulation extinction risk, including synchrony in population size between subpopulations, metapopulation size and the magnitude of fluctuations in population size. Theoretically, each of these is influenced by the rate of migration between subpopulations. Here we report on an experiment where we manipulated migration rate within metapopulations of the freshwater zooplankton Daphnia magna to examine how migration influenced each of these demographic variables, and subsequent effects on metapopulation extinction. In addition, our experimental procedures introduced unplanned but controlled differences between metapopulations in light intensity, enabling us to examine the relative influences of environmental and demographic factors. We found that increasing migration rate increased subpopulation synchrony. We failed to detect effects of migration on population size and fluctuations in population size at the metapopulation or subpopulation level, however. In contrast, light intensity did not influence synchrony, but was positively correlated with population size and negatively correlated with population fluctuation. Finally, synchrony did not influence time to extinction, while population size and the magnitude of fluctuations did. We conclude that environmental factors had a greater influence on extinction risk than demographic factors, and that metapopulation size and fluctuation were more important to extinction risk than metapopulation synchrony.     

苜蓿草地生境丧失与破碎化对昆虫物种丧失与群落重建的影响

生境破碎化包括生境丧失与破碎化两个相对独立的过程,为探讨这两个过程各自对生物多样性的影响,本文利用苜蓿草地实验模型系统(EMS)构建了36个小区研究不同生境丧失与破碎化对昆虫群落及不同类群的影响,包括18个破碎化小区与18个连续小区,破碎化小区全部采用1 m×1 m(H=1)破碎,连续小区苜蓿连片(H=0),生境丧失采...     

Matrix context and patch quality jointly determine diversity in a landscape‐scale experiment

The biodiversity of a habitat patch is predicted to be driven in part by interactions between patch quality and landscape context (i.e. type of regional matrix), but these interactions are rarely explored experimentally. Understanding the interaction between patch quality and matrix context can provide insight into the kind of dynamics that best describe a metacommunity and help predict how the diversity of a patch will respond to environmental change at different scales. We conducted a landscape‐scale experiment to examine how regional and local aspects of the terrestrial matrix interact to affect biodiversity within artificial ponds designed to mimic generic features of freshwater ephemeral ponds. We manipulated both the kind of matrix surrounding ponds (open canopy grassland, pine forest, and hardwood forest) and pond quality (three different types of leaf litter substrate). Ponds were left open to natural colonization for three months by aquatic insects and amphibians. The terrestrial matrix had consistent and strong effects on biodiversity throughout the experiment: ponds in open canopy areas had more animal morphotypes than ponds in pine or hardwood forests. Leaf litter type affected biodiversity during the experiment, with more animal morphotypes in ponds with higher quality litter than ponds with lower quality litter, and this effect was stronger in open canopy areas. The effect of leaf litter, however, disappeared by the end of the experiment. Our results suggest that the matrix surrounding patches has strong effects on community dynamics and biodiversity within patches, and conservation efforts aimed at maintaining biodiversity requires simultaneous consideration of both matrix habitats and habitat patches.     

Patch occupancy in the endangered butterfly Lycaena helle in a fragmented landscape: effects of habitat quality, patch size and isolation

While there is agreement that both habitat quality and habitat network characteristics (such as patch size and isolation) contribute to the occupancy of patches by any given species, the relative importance of these factors is under debate. This issue is of fundamental ecological importance, and moreover of special concern for conservation biologists aiming at preserving endangered species. Against this background we investigated patch occupancy in the violet copper Lycaena helle, one of the rarest butterfly species in Central Europe, in the Westerwald area (Rhineland-Palatinate, Western Germany). Occupied (n = 102) differed from vacant (n = 128) patches in altitude, size, connectivity, availability of wind shelter, in the abundance of the larval host-plant, in the abundance of a grass species indicating favorable habitat conditions and in the abundance of nitrophilous plants. Overall, patch occupancy was primarily determined by patch size, connectivity and the abundance of the larval host plant, while all other parameters of habitat quality were of subordinate importance. Therefore, our findings suggest that even for extremely sedentary species such as L. helle habitat networks are decisive and—next to the preservation of habitat quality—need to be an integral part of any conservation management for this species.     

Protein and carbohydrate intake influence sperm number and fertility in male cockroaches,but not sperm viability

It is commonly assumed that because males produce many, tiny sperm, they are cheap to produce. Recent work, however, suggests that sperm production is not cost-free. If sperm are costly to produce, sperm number and/or viability should be influenced by diet, and this has been documented in numerous species. Yet few studies have examined the exact nutrients responsible for mediating these effects. Here, we quantify the effects of protein (P) and carbohydrate (C) intake on sperm number and viability in the cockroach Nauphoeta cinerea, as well as the consequences for male fertility. We found the intake of P and C influenced sperm number, being maximized at a high intake of diets with a P : C ratio of 1 : 2, but not sperm viability. The nutritional landscapes for male fertility and sperm number were closely aligned, suggesting that sperm number is the major determinant of male fertility in N. cinerea. Under dietary choice, males regulate nutrient intake at a P : C ratio of 1 : 4.95, which is midway between the ratios needed to maximize sperm production and pre-copulatory attractiveness in this species. This raises the possibility that males regulate nutrient intake to balance the trade-off between pre- and post-copulatory traits in this species.