Small-scale Habitat Fragmentation Research Articles

Subtle Effects of Experimental Grassland Fragmentation on Density, Species Composition and Functional Dispersion of Gastropods

The fragmentation of continuous habitats has significant consequences for species and for the functional diversity of plant and animal communities. Fragmentation effects can be indirect, can occur at different spatial scales and may vary over years. Small fragmentation-related effects may only be detected in standardized, controlled field experiments accounting for the natural variation in environmental conditions and in remnants of habitat. Using a non-invasive trapping approach, we examined the responses of terrestrial gastropods (snails and slugs) to small-scale habitat fragmentation in a controlled experiment conducted in three species-rich, nutrient-poor calcareous grasslands in the Jura Mountains, Switzerland, over four years. We found site-specific differences in species richness, individual density, and species composition. Experimental grassland fragmentation did not significantly affect species richness or density, but affected functional dispersion (a measure of functional diversity) in the final year, indicating that fragmentation-related changes may occur with a time delay. Similarly, experimental fragmentation influenced the mean shell size of the snail assemblage and the proportions of individuals with certain life-history traits or habitat preferences in some years. The observed fragmentation effects were subtle and varied over time, underlining the importance of controlled field experiments.

Comparative genomic analysis of three co-occurring annual Asteraceae along micro-geographic fragmentation scenarios

This is the first population genomic analysis that examines micro-evolutionary changes in co-occurring plant species, in fragmented habitats, along a precipitation gradient. We applied Genotype-by-Sequencing (GBS) on three different annual Asteraceae on the same sites that share similar life history strategies, but different pollination and dispersal strategies (Catananche lutea, Geropogon hybridus, Urospermum picroides).We tested if the genetic diversity for all species correlates with effective population sizes along the precipitation gradient and whether therefore genetic drift drives evolution at range edges. However, our results support this hypothesis for only one species (C. lutea) but refute it for the other two. Potential genomic signals of adaptation to the high precipitation gradient were found only in one species (U. picroides). We also tested if species with complex pollination and diversified dispersal strategies are less affected by small scale habitat fragmentation, but the opposite is true. Biological differences between the species studied (pollination and dispersal) explain population genetic differences along the precipitation gradient at range edges rather than environmental filters. Pairwise correlation analyses showed no or only weak similarities in the accumulation of mutations in the different species.Our results suggest that the processes driving evolution in different co-occurring species are different, so that most genomic similarities in our investigations may only represent temporary stages in evolution.

FragMAP: a tool for long-term and cooperative monitoring and analysis of small-scale habitat fragmentation using an unmanned aerial vehicle

ABSTRACTSmall patches of fragmented landscape cannot be resolved using remote-sensing satellite images and they are too numerous and too irregular to be measured easily and efficiently on the ground. As a result, studies of habitat fragmentation at small scales are inadequate. The major objective of this study is to develop a practical tool that can be used for the long-term and cooperative monitoring and analysis of small-scale habitat fragmentation with an unmanned aerial vehicle (UAV). This tool has two components. The software consists of: (1) field trip preparation; (2) auto-piloting; (3) image location and selection; and (4) image analysis. The hardware comprises: (1) a desktop computer; (2) a Phantom 3 Professional four-wheel drone (DJI Innovation Company Inc.); and (3) a Huawei Pad with an Android 4.4 operating system. This tool was demonstrated during field trips on the Qinghai–Tibetan Plateau (QTP) in the summer of 2015. It is stable, robust, efficient, and easy to operate. More importantly, it is designed to be used in a cooperative way within a team and among groups and for long-term repeated monitoring. This tool is suitable for widespread deployment to establish a monitoring network studying small-scale habitat fragmentation status and rate of change.

Resisting habitat fragmentation: High genetic connectivity among populations of the frugivorous bat Carollia castanea in an agricultural landscape

Anthropogenically dominated landscapes are frequently a patchwork composed of manmade structures and natural habitat remnants. Especially tropical landscapes are progressively turning into such heterogeneous mosaics leading to simplification of animal communities and (partial) isolation of the scattered survivors. Modern molecular approaches provide powerful tools to detect discontinuities in gene flow among local populations. The aim of this study was to evaluate genetic connectivity on a small geographic scale among local bat populations that inhabit forest fragments in an agricultural matrix in north-east Costa Rica. We focused on Carollia castanea (Phyllostomidae), a small frugivorous bat that mainly feeds on pepper plants. We analyzed DNA sequences of the mitochondrial D-loop of 173 adult individuals. There was no significant global population differentiation detectable (FST=0.008, p=0.17) and regular gene flow among populations was indicated by low pairwise FST-values, even in highly fragmented areas. Solely with increasing geographic distance gene flow was weakened, indicated by a significant isolation by distance pattern (R2=0.55, p<0.05). Our study shows that C. castanea can cope better with small-scale habitat fragmentation than other phyllostomid bat species, at least in an agriculturally dominated landscape. This is probably because of its tolerance toward disturbed habitats for foraging that enables it to maintain genetic exchange among populations that are separated by areas under human influence.

Effects of small-scale habitat fragmentation on predator–prey interactions in a temperate sea grass system

During the last decades, fragmentation has become an important issue in ecological research. Habitat fragmentation operates on spatial scales ranging over several magnitudes from patches to landscapes. We focus on small-scale fragmentation effects relevant to animal foraging decision making that could ultimately generate distribution patterns. In a controlled experimental environment, we tested small-scale fragmentation effects in artificial sea grass on the feeding behaviour of juvenile cod (Gadus morhua). Moreover, we examined the influence of fragmentation on the distribution of one of the juvenile cod’s main prey resources, the grass shrimp (Palaemon elegans), in association with three levels of risk provided by cod (no cod, cod chemical cues and actively foraging cod). Time spent by cod within sea grass was lower in fragmented landscapes, but total shrimp consumption was not affected. Shrimp utilised vegetation to a greater extent in fragmented treatments in combination with active predation. We suggest that shrimp choose between sand and vegetation habitats to minimize risk of predation according to cod habitat-specific foraging capacities, while cod aim to maximize prey-dependent foraging rates, generating a habitat-choice game between predator and prey. Moreover, aggregating behaviour in grass shrimp was only found in treatments with active predation. Hence, we argue that both aggregation and vegetation use are anti-predator defence strategies applied by shrimp. We therefore stress the importance of considering small-scale behavioural mechanisms when evaluating consequences from habitat fragmentation on trophic processes in coastal environments.

Delayed response in a plant–pollinator system to experimental grassland fragmentation

The fragmentation of natural habitat is considered to be a major threat to biodiversity. Decreasing habitat quality and quantity caused by fragmentation may lead to a disruption of plant-pollinator interactions and to a reduction in sexual reproduction in plant species. We conducted a 6-year field experiment to investigate the effects of small-scale fragmentation on plant-pollinator interactions and genetic diversity in the self-compatible Betonica officinalis. We examined the abundance and composition of pollinators, the foraging behaviour of bumblebees and the performance, outcrossing rate and genetic diversity of B. officinalis after 2 and 6 years in experimentally fragmented nutrient-poor, calcareous grassland in the northern Swiss Jura mountains. Fragments of different size (2.25 and 20.25 m(2)) were isolated by a 5-m-wide strip of frequently mown vegetation. Control plots of corresponding size were situated in adjacent undisturbed grassland. Experimental grassland fragmentation altered the composition of B. officinalis pollinators and reduced their flower visitation rate. Furthermore, the foraging behaviour of bumblebees was changed in the fragments. After 6 years of fragmentation seed weight was higher in fragments than in control plots. However, the densities of B. officinalis rosettes and inflorescences, plant height and inflorescence length were not affected by fragmentation. The outcrossing frequency of B. officinalis growing in fragments was reduced by 15% after 2 years and by 33% after 6 years of experimental fragmentation. This resulted in a significant reduction of the genetic diversity in seedlings emerging in fragments after 6 years. Our study shows that small-scale habitat fragmentation can disturb the interaction between B. officinalis and pollinators resulting in a reduced outcrossing frequency and genetic diversity in plants growing in fragments. However, the response to fragmentation was considerably delayed. This finding strengthens the claim for long-term field experiments with proper replications and controls to assess delayed effects of habitat fragmentation.

Effects of small-scale habitat fragmentation, habitat corridors and mainland dispersal on soil decomposer organisms

Habitat corridors have been suggested to be one possible way to reduce the often negative effects of habitat fragmentation. In the present experiment, we focused on small habitat fragments (humus patches) inhabited by soil decomposer organisms. These fragments were either unconnected or connected with each other by habitat (humus) corridors. Moreover, these systems were either isolated from the mainland by a dispersal barrier (plastic “walls”) or were open to dispersal from the mainland. The fragments and corridors were embedded in a matrix of mineral soil that was expected to be uninhabitable or at least an unpreferred habitat for the organisms studied. Undisturbed forest soil functioned as the mainland. The results showed that habitat fragmentation decreased the abundance of microarthropods (Acari). Presence of corridors affected positively the abundance of mites, but only after the first 4 months of the experiment: later on, this effect disappeared. Furthermore, this “corridor rescue effect” was only seen in the systems isolated from the mainland, whereas in the open systems, dispersal from the mainland apparently overwhelmed the effect of corridors. Also soil fungi benefited from the corridors. The results indicate that soil decomposer organisms, microarthropods in particular, may be useful as model organisms in studies focusing on the ecological consequences of habitat fragmentation. It is also suggested that connecting otherwise isolated small habitat fragments with each other by habitat corridors may increase the persistence time of fragment-inhabiting populations.

Effects of experimental small-scale habitat fragmentation on above- and below-ground plant biomass in calcareous grasslands

The effect of small-scale fragmentation on the above-ground plant biomass was examined in nutrient-poor calcareous grasslands in the northern Swiss Jura mountains in three successive years. In the same field experiment, the fragmentation effect on the below-ground plant biomass was evaluated in 1 year. Additionally, species richness and abundance of plants were recorded. The experimental set-up consisted of 12 blocks with 48 fragments (24 small, 12 medium and 12 large) and 48 corresponding control plots distributed over three study sites. Fragmentation was maintained by frequently mowing the area between the fragments. Three to 5 years after the beginning of the experiment, plant biomass was harvested in all fragments and control plots in late autumn every year. In general, fragments contained more above- and below-ground plant biomass than control plots. The increase in above-ground plant biomass was partly due to an increased density of plants, and partly due to a change in species composition in fragments. In particular, a competitive shift of dominance towards tall grasses and forbs at the expense of smaller forbs was observed. Beside the main fragmentation effect on above-ground plant biomass, interactive effects with year of investigation, study site and plot size were found. This indicates that the observed fragmentation effect is a combined result of various factors acting to a different extent at different sites and plot sizes. The fragmentation-related increase in plant productivity could affect higher trophic levels such as herbivore and predator communities.

Small-scale habitat fragmentation effects on pollinator behaviour: experimental evidence from the bumblebee Bombus veteranus on calcareous grasslands

We examined visiting patterns of pollinators of Betonica officinalis L. (Lamiaceae) in experimentally fragmented calcareous grasslands and corresponding control plots at two study sites (Movelier and Nenzlingen) in the north-western Swiss Jura mountains. Fragments (1.5×1.5 m) were isolated by a 5-m wide strip of frequently mown vegetation while the control plots were situated in the adjacent undisturbed vegetation. The most common pollinator, the bumblebee Bombus veteranus (Apidae), visited fragments 53.7% less frequently than control plots. Furthermore, a change in foraging behaviour of Bombus veteranus was observed. In fragments the bumblebees visited more inflorescences, flew longer total visiting distances and the visiting time per patch tended to be higher than in control plots. The distribution of angles between arrival and departure direction (turning angles) differed from a uniform distribution in fragments but not in control plots. The increased directionality of bumblebee flight might be due to a decrease in floral rewards. Our results show that small-scale habitat fragmentation can affect plant pollination at two levels both relevant for plant fitness. First, lower visitation rates indicate a limitation of pollinators which might result in reduced seed set of the pollinated plant. Second, changes in pollinator behaviour might reduce pollen dispersal among flowers, increase inbreeding and hence reduce genetic variability in populations of this bumblebee pollinated plant.

Territorial Movements of Black-throated Blue Warblers in a Landscape Fragmented by Forestry

AbstractMany forest bird species show inhibition to entering open areas, including crossing habitat gaps. We examined the responses of Black-throated Blue Warblers (Dendroica caerulescens) to conspecific song playback within forest, at clearcut-forest ecotones, and across logging roads to assess movements of this Neotropical migrant into open areas. Males responded readily to song playbacks in all areas, and moved significantly farther into clearcuts than they did within intact forest (40.4 ± 2.9 m and 17.1 ± 1.2 m, respectively). Their singing, aggressive trilling, and alarm-calling rates were highest in response to playback from clearcuts, intermediate during road-crossings, and lowest within forest. Males moved farthest into the oldest regenerating clearcuts (&gt;15 years old), indicating that vegetation structure also influences their movement into open areas. Second-year males were more responsive than older males, moving farther to reach speakers in all areas, and showing a nonsignificant trend of moving farther into clearcuts. We found that extensive movements into open areas occur in response to simulated territorial intrusion, indicating that small-scale habitat fragmentation by forestry may not disrupt territorial movements of that species.

Territorial Movements of Black-throated Blue Warblers in a Landscape Fragmented by Forestry

Many forest bird species show inhibition to entering open areas, including crossing habitat gaps. We examined the responses of Black-throated Blue Warblers (Dendroica caerulescens) to conspecific song playback within forest, at clearcut-forest ecotones, and across logging roads to assess movements of this Neotropical migrant into open areas. Males responded readily to song playbacks in all areas, and moved significantly farther into clearcuts than they did within intact forest (40.4 ± 2.9 m and 17.1 ± 1.2 m, respectively). Their singing, aggressive trilling, and alarm-calling rates were highest in response to playback from clearcuts, intermediate during road-crossings, and lowest within forest. Males moved farthest into the oldest regenerating clearcuts (>15 years old), indicating that vegetation structure also influences their movement into open areas. Second-year males were more responsive than older males, moving farther to reach speakers in all areas, and showing a nonsignificant trend of moving farther into clearcuts. We found that extensive movements into open areas occur in response to simulated territorial intrusion, indicating that small-scale habitat fragmentation by forestry may not disrupt territorial movements of that species.

Experimental effects of habitat fragmentation on old-field canopy insects: community, guild and species responses.

We examined the effects of habitat fragmentation on the species distributions, guild membership, and community structure of old-field insects using a fine-scale experimental approach. A continuous 1-ha goldenrod field was fragmented into four treatments that varied in both patch size and degree of isolation. Each treatment was replicated four times and arranged in a Latin square design. Canopy insects in fragmented patches were sampled with sweep nets during early and late summer 1995. The species richness of insects was significantly lower in fragmented than in unfragmented treatments during July, but was similar among treatments in September. Overall community abundance showed no treatment effect during either month. We also found significant row and column effects, suggesting there was spatial heterogeneity in species richness and abundance apart from treatment effects. Differences in species richness during July were primarily due to the loss of rare species in highly fragmented plots. Overall abundance was less responsive to community change because deletions of rare species in fragmented areas were not detected in abundance analyses. Four feeding guilds showed different responses to fragmentation: the species richness of sucking herbivores and the abundance of parasitoids were significantly reduced by fragmentation but predators and chewing herbivores were largely unaffected. Analyses of a subset of individual species within guilds suggest that the greater effects of fragmentation on sucking herbivores and parasitoids may be due to the degree of habitat specificity of guild members. The effects of small-scale habitat fragmentation were therefore detectable at the level of community, guild, and individual species. Changes in species richness, guild structure and species distributions were likely due to differential effects of habitat alteration on individual movements and patch selection rather than dispersal or demographic change. Nonetheless, the selective loss of rare species, differential guild effects and changes in species occupancy that we found in this small-scale experiment are also factors that are likely to operate in fragmented habitats over broader spatial scales.