Unconnected Patches Research Articles

Enhancing maximum sustainable yield in a patchy prey–predator environment

In this paper, we investigate a prey–predator community of fish coexisting in a multi-patches model, where different fishing patches are interconnected through migration terms. Only the predator is caught, while the prey grows logistically on each patch. The main objective of our research is to compare the maximum sustainable yield achieved in two contrasting scenarios: unconnected patches and connected patches with rapid stock movements. We show that the total maximum sustainable yield for the connected patches can be greater than the sum of the maximum sustainable yield on each isolated patch. The analysis of the model allows us to establish the conditions under which one of the two cases is more favorable from the viewpoint of yield. As a result, we provide a complete classification for all possible cases. This valuable information can be used to assist decision-makers in selecting the best management strategy for a particular fishery.

Transient effects of corridors on polygyne fire ants over a decade

Abstract Although corridors are frequently regarded as a way to mitigate the negative effects of habitat fragmentation, concerns persist that corridors may facilitate the spread of invasive species to the detriment of native species. The invasive fire ant, Solenopsis invicta, has two social forms. The polygyne form has limited dispersal abilities relative to the monogyne form. Our previous work in a large‐scale corridor experiment showed that in landscapes dominated by the polygyne form, fire ant density was higher and native ant species richness was lower in habitat patches connected by corridors than in unconnected patches. We expected that these observed corridor effects would be transient, that is, that fire ant density and native ant species richness differences between connected and unconnected patches would diminish over time as fire ants eventually fully established within patches. We tested this prediction by resampling the three landscapes dominated by polygyne fire ants 6 to 11 years after our original study. Differences in fire ant density between connected and unconnected habitat patches in these landscapes decreased, as expected. Differences in native ant species richness were variable but lowest in the last 2 years of sampling. These findings support our prediction of transient corridor effects on this invasive ant and stress the importance of temporal dynamics in assessing population and community impacts of habitat connectivity.

Topological distance-constrained feature descriptor learning model for vessel matching in coronary angiographies

BackgroundFeature matching technology is vital to establish the association between virtual and real objects in virtual reality and augmented reality systems. Specifically, it provides them with the ability to match a dynamic scene. Many image matching methods, of which most are deep learning-based, have been proposed over the past few decades. However, vessel fracture, stenosis, artifacts, high background noise, and uneven vessel gray-scale make vessel matching in coronary angiography extremely difficult. Traditional matching methods perform poorly in this regard. MethodsIn this study, a topological distance-constrained feature descriptor learning model is proposed. This model regards the topology of the vasculature as the connection relationship of the centerline. The topological distance combines the geodesic distance between the input patches and constrains the descriptor network by maximizing the feature difference between connected and unconnected patches to obtain more useful potential feature relationships. ResultsMatching patches of different sequences of angiographic images are generated for the experiments. The matching accuracy and stability of the proposed method is superior to those of the existing models. ConclusionsThe proposed method solves the problem of matching coronary angiographies by generating a topological distance-constrained feature descriptor.

Ongoing accumulation of plant diversity through habitat connectivity in an 18-year experiment.

Deleterious effects of habitat fragmentation and benefits of connecting fragments could be significantly underestimated because changes in colonization and extinction rates that drive changes in biodiversity can take decades to accrue. In a large and well-replicated habitat fragmentation experiment, we find that annual colonization rates for 239 plant species in connected fragments are 5% higher and annual extinction rates 2% lower than in unconnected fragments. This has resulted in a steady, nonasymptotic increase in diversity, with nearly 14% more species in connected fragments after almost two decades. Our results show that the full biodiversity value of connectivity is much greater than previously estimated, cannot be effectively evaluated at short time scales, and can be maximized by connecting habitat sooner rather than later.

Habitat connectivity enhances diversity

Plant Ecology Fragmentation of ecosystems leads to loss of biodiversity in the remaining habitat patches, but retaining connecting corridors can reduce these losses. Using long-term data from a large, replicated experiment, Damschen et al. show quantitatively how these losses are reduced. In their pine savanna system, corridors reduced the likelihood of plant extinction in patches by about 2% per year and increased the likelihood of patch colonization by about 5% per year. These benefits continued to accrue over the course of the 18-year experiment. By the end of monitoring, connected patches had 14% more species than unconnected patches. Restoring habitat connectivity may thus be a powerful technique for conserving biodiversity, and investment in connections can be expected to magnify conservation benefit. Science , this issue p. [1478][1] [1]: /lookup/doi/10.1126/science.aax8992

Landscape-mediated edge effect in temperate deciduous forest: implications for oak regeneration

Although the edge effect is known to be an important factor influencing the recruitment of trees in temperate forests, little is known of its synergistic relationships with landscape and fragment attributes. We investigated how the edge effect on regeneration of oaks (Quercus spp.) varies with respect to fragment geometry, connectivity and landscape composition. We recorded oak sapling density along edge-interior gradients in 29 forest fragments at the periphery of Mexico City and examined the data with Generalized Additive Models. A nonlinear and landscape-mediated edge effect was supported by data, including the interactions of the edge distance with patch connectivity, shape and size. Saplings were more abundant at a distance of ca. 50 m from the edge of small, large and connected patches, but large patches also exhibited reduced recruitment towards the interior of the patch. Conversely, sapling density in simple-shaped or connected patches was lower at the edge, exhibiting linear and concave-down increase trends towards the interior of patches, respectively. Boundary conditions could be interacting with interior forest conditions, making regeneration more frequent at 50 m from the edge. Shady and cooler sites in large patches may be inhibiting oak regeneration. The activity of acorn-dispersing animals and oak predators may increase in unconnected patches, thus increasing the likelihood of edge effects. These results provide insights into the restoration of temperate forest patches in heterogeneous fragmented landscapes.

Tectonic slicing of subducting oceanic crust along plate interfaces: Numerical modeling

AbstractMultikilometer‐sized slivers of high‐pressure low‐temperature metamorphic oceanic crust and mantle are observed in many mountain belts. These blueschist and eclogite units were detached from the descending plate during subduction. Large‐scale thermo‐mechanical numerical models based on finite difference marker‐in‐cell staggered grid technique are implemented to investigate slicing processes that lead to the detachment of oceanic slivers and their exhumation before the onset of the continental collision phase. In particular, we investigate the role of the serpentinized subcrustal slab mantle in the mechanisms of shallow and deep crustal slicing. Results show that spatially homogeneous serpentinization of the sub‐Moho slab mantle leads to complete accretion of oceanic crust within the accretionary wedge. Spatially discontinuous serpentinization of the slab mantle in form of unconnected patches can lead to shallow slicing of the oceanic crust below the accretionary wedge and to its deep slicing at mantle depths depending on the patch length, slab angle, convergence velocity and continental geothermal gradient. P‐T paths obtained in this study are compared to natural examples of shallow slicing of the Crescent Terrane below Vancouver Island and deeply sliced crust of the Lago Superiore and Saas‐Zermatt units in the Western Alps.

Landscape corridors can increase invasion by an exotic species and reduce diversity of native species.

Landscape corridors are commonly used to mitigate negative effects of habitat fragmentation, but concerns persist that they may facilitate the spread of invasive species. In a replicated landscape experiment of open habitat, we measured effects of corridors on the invasive fire ant, Solenopsis invicta, and native ants. Fire ants have two social forms: polygyne, which tend to disperse poorly but establish at high densities, and monogyne, which disperse widely but establish at lower densities. In landscapes dominated by polygyne fire ants, fire ant abundance was higher and native ant diversity was lower in habitat patches connected by corridors than in unconnected patches. Conversely, in landscapes dominated by monogyne fire ants, connectivity had no influence on fire ant abundance and native ant diversity. Polygyne fire ants dominated recently created landscapes, suggesting that these corridor effects may be transient. Our results suggest that corridors can facilitate invasion and they highlight the importance of considering species' traits when assessing corridor utility.

Habitat corridors alter relative trophic position of fire ants

Habitat fragmentation disrupts species movement, leading to local extinctions and altered community structure. Habitat corridors, which connect isolated patches of habitat and facilitate movement between patches, provide a potential solution to these negative impacts. However, most studies to date have examined the movement of species alone without considering emergent effects on the community (e.g., altered trophic structure). We use large‐scale, experimental landscapes and nitrogen stable isotopes ratios (δ15N) of a common generalist consumer (the fire ant, Solenopsis invicta) to determine how corridors affect trophic structure. Thus, because the fire ant is a species whose trophic position is flexible and whose diet typically reflects local prey availability, we assume that shifts in fire ants' trophic position between connected and isolated patches are likely to reflect shifts in patch trophic structure. We found that colonies in isolated patches had lower means and ranges of δ15N than colonies in otherwise similar connected patches, suggesting that corridors may increase fire ants' trophic position and breadth, respectively. Previous work in our landscapes documented higher species richness of plants in connected than unconnected patches. Patch means of ant δ15N were positively correlated with plant richness, suggesting that increased plant richness may influence the observed responses in fire ant δ15N. Together these results suggest that fragmentation may reduce trophic position and narrow trophic breadth of dietary generalists such as the fire ant. These shifts likely reflect an alteration of food webs in isolated patches. Our results suggest that corridors may be effective in preventing or reducing such alterations.

Large-scale experimental landscapes reveal distinctive effects of patch shape and connectivity on arthropod communities

The size, shape, and isolation of habitat patches can affect organism behavior and population dynamics, but little is known about the relative role of shape and connectivity in affecting ecological communities at large spatial scales. Using six sampling sessions from July 2001 until August 2002, we collected 33,685 arthropods throughout seven 12-ha experimental landscapes consisting of clear-cut patches surrounded by a matrix of mature pine forest. Patches were explicitly designed to manipulate connectivity (via habitat corridors) independently of area and edge effects. We found that patch shape, rather than connectivity, affected ground-dwelling arthropod richness and beta diversity (i.e. turnover of genera among patches). Arthropod communities contained fewer genera and exhibited less turnover in high-edge connected and high-edge unconnected patches relative to low-edge unconnected patches of similar area. Connectivity, rather than patch shape, affected the evenness of ground-dwelling arthropod communities; regardless of patch shape, high-edge connected patches had lower evenness than low- or high-edge unconnected patches. Among the most abundant arthropod orders, increased richness in low-edge unconnected patches was largely due to increased richness of Coleoptera, whereas Hymenoptera played an important role in the lower evenness in connected patches and patterns of turnover. These findings suggest that anthropogenic habitat alteration can have distinct effects on ground-dwelling arthropod communities that arise due to changes in shape and connectivity. Moreover, this work suggests that corridors, which are common conservation tools that change both patch shape and connectivity, can have multiple effects on arthropod communities via different mechanisms, and each effect may alter components of community structure.

Edge-mediated patterns of seed removal in experimentally connected and fragmented landscapes

While biological reserves remain central to biodiversity conservation, the amount of area available for terrestrial reserves may be inadequate for many taxa. Biodiversity spillover—the promotion of diversity in matrix areas surrounding reserves—might help address this shortfall in reserve area. However, the mechanistic underpinning of spillover remains uninvestigated. Two fundamental processes—seed dispersal and establishment—might generate plant biodiversity spillover. Here, we investigate the role of establishment in promoting spillover by assessing post-dispersal seed predation, a key component of establishment, in the matrix of a replicated, large-scale habitat fragmentation experiment, where spillover is elevated around patches connected by landscape corridors. Our results show that matrix seed predation may constrain the distance of this spillover effect by reducing establishment: seed removal was least at the matrix edge and increased further into the matrix. We found some support for matrix seed predation underpinning previously reported landscape-level variation in spillover. Of the three species we investigated, two showed evidence for elevated seed predation in the matrix surrounding the unconnected patches around which the lowest levels of spillover occur. However, seed predation did not explain connectivity-enhanced spillover, suggesting that seed dispersal likely drives this pattern. Management activities that increase seed deposition in the matrix may have beneficial effects via spillover. Our work also illustrates that matrix-mediated gradients in seed predation may be widespread, but likely vary depending upon matrix composition and the ecological system under consideration. In fragmented landscapes, this gradient could impact the distribution, abundance, and spread of plant species.

Forest corridors facilitate movement of tropical forest birds after experimental translocations in a fragmented Neotropical landscape in Mexico

Abstract:We evaluated effects of corridors between forest fragments surrounded by pastures in tropical Mexico. We used experimental translocations and capture–recapture data to measure the proportion of birds returning and time to return after translocation between connected and unconnected patches (five replicates for each treatment). Depending on each species’ degree of forest dependence (forest-restricted and forest-unrestricted species), we assigned birds to two groups to evaluate influence of species characteristics on effects of corridors on movement. Birds translocated between connected patches (n = 75) were seven times more likely to be recaptured in their original capture site when compared with birds translocated between unconnected patches (n = 109). Effects differed among the two species groups. In the presence of corridors, 46% of forest-unrestricted birds returned to the capture site while only 5% returned between unconnected patches. Forest-restricted birds showed similar results, but were only twice as likely to return to a connected capture site. Birds translocated between unconnected patches took longer to return than birds translocated between connected patches. The strong positive effect of corridors on movement, even for forest-unrestricted species, suggests that forested corridors facilitate bird movement and help maintain connectivity even in this highly fragmented landscape.

Patch occupancy by squirrels in fragmented deciduous forest: effects of behavior

We tested whether species-specific behavioral traits could explain patterns of habitat patch occupancy by five different squirrel species in Ontario, Canada: the northern and southern flying squirrel (Glaucomys sabrinus and Glaucomys volans), the North American red squirrel (Tamiasciurus hudsonicus), the eastern chipmunk (Tamias striatus), and the eastern gray squirrel (Sciurus carolinensis). Flying squirrel species exhibit group nesting in winter, which may put them at risk of extirpation in small patches with few individuals to contribute to group nests. Flying squirrels are also volant, potentially making non-treed matrix a barrier. Our surveys revealed that G. sabrinus was most likely to occur in large patches that were embedded in landscapes with low connectivity, and least likely to occur in small patches in highly connected landscapes. Conversely, G. volans was most likely to occur in large, well-connected patches and least likely to occur in small, unconnected patches. Patch occupancy by the cursorial squirrels was not strongly influenced by patch area or isolation. These findings reinforce previous studies suggesting that an understanding of species-specific traits such as behavior is an important consideration when interpreting habitat fragmentation effects.

Matrix effects on plant-frugivore and plant-predator interactions in forest fragments

Structural features of both habitat remnants and surrounding matrix can be important for explaining plant population dynamics and ecosystem functions in human-impacted landscapes. However, little is known about how the structural features of the adjacent matrix affect biotic interactions and whether such context effects are subject to temporal variations. Using the hawthorn Crataegus monogyna in northern Spain, we studied matrix effects on two sequential plant-animal interactions, frugivory by birds and postdispersal seed predation by rodents. Using Hierarchical Linear Models, we compared the magnitude of both interactions on trees located in two patch types that strongly differed in structural features of the adjacent matrix habitat: patches totally surrounded by a degraded, structurally contrasted pastures (unconnected patches), and trees growing in patches adjacent to a lowly degraded, structurally similar mature forests (connected patches). We compared outcomes for 2005 and 2006, which were years with strong differences in community-wide fruit and seed abundance. Frugivory rate did not differ between patch types in either year, likely related to high mobility of birds. Seed predation rates were higher in unconnected patches than in connected ones, but only in 2005. We conclude that strong interannual fluctuations in resource availability are not rare in temperate systems and that recruitment rates could be frequently reduced within unconnected patches, thus collapsing plant regeneration processes of hawthorn populations. Overall, our results suggest that generalizations about potential effects of the matrix on plant-animal interactions within remnant patches must consider: (1) species-specific habitat responses of the organisms, (2) suitability of neighbouring habitats in terms of food supply, and (3) temporal variations in plant-resource availability for interacting animals.

Effects of Corridors on Genetics of a Butterfly in a Landscape Experiment

Abstract To investigate the possible role of landscape connectivity on the genetic structure of isolated populations, we examined the effects of habitat corridors on the population genetics of a vagile butterfly species, Junonia coenia, within a large-scale, experimental system. Using allozyme electrophoresis, a total of nine loci were identified and scored, six of which exhibited polymorphism. Our data demonstrated consistently higher levels of expected (He) and observed (Ho) heterozygosity in butterflies sampled from patches connected by corridors compared to unconnected patches. A t-test comparing He and H0 in connected versus unconnected patches found a marginally significant difference in one locus, the glycolytic enzyme phosphoglucose isomerase (PGI). Connected patches exhibited overall lower F ST values compared to unconnected patches, indicating potentially increased levels of gene flow due to corridors. Our results support previous investigations on dispersal and population size for J. coenia, an...

Reconstruction of source distributions from sound pressures measured over discontinuous regions: Multipatch holography and interpolation

In the present work, a method of alternating orthogonal projections is described in the context of near-field acoustical holography; it allows missing (or "not measured") data to be recovered, thus relieving the strictness of measurement requirements related to the use of the discrete Fourier transform. The method described here provides the detailed foundation for the patch holography procedure that has previously been introduced to mitigate finite measurement aperture effects by allowing the sound field to be iteratively extended beyond the measurement aperture. It is also shown that the latter iterative algorithm can be used regardless of the spatial distribution of measured data: i.e., patches can be discontinuous. Numerical simulations performed by using a synthetic sound field created by a point-driven, simply supported plate were used to demonstrate the latter point. In particular, a multipatch holography procedure is described that allows a source distribution to be reconstructed from the hologram pressure measured over multiple, unconnected patches. It is finally shown that a related approach allows spatial resolution enhancement by interpolation between measured points.

CORRIDORS CAUSE DIFFERENTIAL SEED PREDATION

Corridors that connect disjunct populations are heavily debated in conservation, largely because the effects of corridors have rarely been evaluated by replicated, large‐scale studies. Using large‐scale experimental landscapes, we found that, in addition to documented positive effects, corridors also have negative impacts on bird‐dispersed plants by affecting seed predation, and that overall predation is a function of the seeds' primary consumer (rodents or arthropods). Both large‐seeded Prunus serotina and small‐seeded Rubus allegheniensis experienced greater predation in connected patches. However, P. serotina experienced significantly less seed predation compared to R. allegheniensis in unconnected patches, due to decreased impacts of rodent seed predators on this large‐seeded species. Viewed in light of previous evidence that corridors have beneficial impacts by increasing pollination and seed dispersal, this work demonstrates that corridors may have both positive and negative effects for the same plant species at different life stages. Moreover, these effects may differentially affect plant species within the same community: seeds primarily consumed by rodents suffer less predation in unconnected patches. By shifting the impact of rodent and arthropod seed predators, corridors constructed for plant conservation could lead to shifts in the seed bank.

PATCH SHAPE, CONNECTIVITY, AND FORAGING BY OLDFIELD MICE (PEROMYSCUS POLIONOTUS)

We examined how corridors and patch shape affect foraging by the oldfield mouse (Peromyscus polionotus )b y deploying foraging trays and live traps in experimental landscapes with 3 different patch types: patches connected with a corridor, unconnected patches with projecting corridorlike portions (‘‘winged’’ patches), and unconnected rectangular patches. Corridors did not lead to different levels of activity of P. polionotus among the 3 patch types. Rather, corridors influenced activity by changing patch shape: foraging in seed trays and total number of captures of P. polionotus tended to be greater at the patch center than at the patch edge, but only in connected and winged patches where corridors or wings increased the amount of patch edge relative to the amount of core habitat in the patch. P. polionotus avoided open microhabitats near the patch edge in winged and connected patches, but not open microhabitats near the patch interior, suggesting that predation risk caused shifts in foraging near edges in connected and winged patches. Foraging in corridors and wings was generally low, suggesting that both are high-risk habitats where predation risk is not ameliorated by proximity to vegetative cover. By changing patch shape, corridors caused changes in within-patch activity of P. polionotus, changing foraging patterns and potentially altering the dynamics of P. polionotus and the seeds they consume.

Habitat corridors function as both drift fences and movement conduits for dispersing flies

Corridors connect otherwise isolated habitat patches and can direct movement of animals among such patches. In eight experimental landscapes, we tested two hypotheses of how corridors might affect dispersal behavior. The Traditional Corridor hypothesis posits that animals preferentially leave patches via corridors, following them into adjacent patches. The Drift Fence hypothesis posits that animals dispersing through matrix habitat are diverted into patches with corridors because they follow corridors when encountered. House flies (Musca domestica L.), a species that prefers the habitat of our patches and corridors, were released in a central patch (100x100 m) and recaptured in peripheral patches that were or were not connected by a corridor. Flies were captured more frequently in connected than unconnected patches, thereby supporting the Traditional Corridor hypothesis. The Drift Fence hypothesis was also supported, as flies were captured more frequently in unconnected patches with blind (dead end) corridors than in unconnected patches of equal area without blind corridors. A second experiment tested whether these results might be dependent on the type of patch-matrix boundary encountered by dispersing flies and whether edge-following behavior might be the mechanism underlying the observed corridor effect in the first experiment. We recorded dispersal patterns of flies released along forest edges with dense undergrowth in the forest ("closed" edges) and along edges with little forest understory ("open" edges). Flies were less likely to cross and more likely to follow closed edges than open edges, indicating that when patch and corridor edges are pronounced, edge-following behavior of flies may direct them along corridors into connected patches. Because edges in the first experiment were open, these results also suggest that corridor effects for flies in that experiment would have been even stronger if the edges around the source patches and corridors had been more closed. Taken together, our results suggest that corridors can affect dispersal of organisms in unappreciated ways (i.e., as drift fences) and that edge type can alter dispersal behavior.

AN EXPERIMENTAL TEST OF WHETHER HABITAT CORRIDORS AFFECT POLLEN TRANSFER

Negative effects of habitat fragmentation are thought to be diminished when habitat patches are joined by a corridor. A key assumption is that corridors facilitate ex- change rates of organisms between otherwise isolated patches. If the organisms are pol- linators, corridors may be important for maintaining genetically viable populations of the plants that they pollinate. We tested the hypothesis that corridors increase the movement of insect pollinators into patches of habitat and thereby increase pollen transfer for two species of plants, one pollinated by butterflies (Lantana camara) and the other by bees and wasps (Rudbeckia hirta). We worked in an experimental landscape consisting of 40 --1- ha patches of early-successional habitat in a matrix of forest. Within each of eight exper- imental units, two patches were connected by a corridor (150 x 25 m), and three were not. Patch shape varied to control for the area added by the presence of a corridor. Differences in patch shape also allowed us to test alternative hypotheses of how corridors might function. The Traditional Corridor Hypothesis posits that corridors increase immigration and emi- gration by functioning as movement conduits between patches. The Drift Fence Hypothesis posits that corridors function by capturing organisms dispersing through the matrix, redirecting them into associated habitat patches. Using fluorescent powder to track pollen, we found that pollen transfer by butterflies between patches connected by a corridor was significantly higher than between unconnected patches (all values mean ? 1 SE: 59% ? 9.2% vs. 25% ? 5.2% of flowers receiving pollen). Likewise, pollen transfer by bees and wasps was significantly higher between connected patches than between unconnected patch- es (30% ? 4.2% vs. 14.5% ? 2.2%). These results support the Traditional Corridor Hy- pothesis. There was little support, however, for the Drift Fence Hypothesis. To generalize our results to a larger scale, we measured the probability of pollen transfer by butterflies as a function of distance along a 2000 x 75 m corridor. Pollen transfer probability expo- nentially declined with respect to distance and successfully predicted pollen transfer prob- ability on the scale of our previous experiment. These results suggest that corridors facilitate pollen transfer in fragmented landscapes.