9 research outputs found
Predicted thresholds for natural vegetation cover to safeguard pollinator services in agricultural landscapes
This is the author accepted manuscriptThe conversion of natural vegetation into cultivated land can cause pollinator declines and thereby degrade pollination services to crops and wildflowers. The effect of landscape composition on pollinator abundance is well established, but its impact on pollination intensity and crop yield is not fully resolved. We therefore studied pollination of two crops in India, brinjal (Solanum melongena) and mustard (Brassica nigra), along a landscape-scale gradient in habitat transformation from forest-dominated natural vegetation to intensive cultivation. We quantified the pollination requirements (pollen receipt-seed set relationships) of the crops and the levels of pollen delivery by their principal pollinators, bees. Combining these with field surveys of pollinator abundance, we modelled the levels of pollination service to fields along the landscape gradient. Projected pollination services declined as the area occupied by natural vegetation decreased. We identified thresholds at which bee pollination no longer supported maximum seed set, which were landscapes with approximately one quarter (27 %) of nearby natural vegetation for brinjal fields and one fifth (18 %) for mustard. Our findings indicate that preserving or restoring the cover of natural habitats above these minimum thresholds could be a valuable strategy for maintaining pollinator abundance and safeguarding yield in these bee-pollinated crops.Darwin Initiativ
Second-order topological superconductor via noncollinear magnetic texture
We put forth a theoretical framework for engineering a two-dimensional (2D)
second-order topological superconductor (SOTSC) by utilizing a heterostructure:
incorporating noncollinear magnetic textures between an s-wave superconductor
and a 2D quantum spin Hall insulator. It stabilizes the higher order
topological superconducting phase, resulting in Majorana corner modes (MCMs) at
four corners of a 2D domain. The calculated non-zero quadrupole moment
characterizes the bulk topology. Subsequently, through a unitary
transformation, an effective low-energy Hamiltonian reveals the effects of
magnetic textures, resulting in an effective in-plane Zeeman field and
spin-orbit coupling. This approach provides a qualitative depiction of the
topological phase, substantiated by numerical validation within exact
real-space model. Analytically calculated effective pairings in the bulk
illuminate the microscopic behavior of the SOTSC. The comprehension of MCM
emergence is aided by a low-energy edge theory, which is attributed to the
interplay between effective pairings of (px + py )-type and (px + ipy )-type.
Our extensive study paves the way for practically attaining the SOTSC phase by
integrating noncollinear magnetic textures
Topological Superconductivity by Engineering Noncollinear Magnetism in Magnet/ Superconductor Heterostructures: A Realistic Prescription for 2D Kitaev Model
We report on a realistic and rather general scheme where noncollinear
magnetic textures proximitized with the most common -wave superconductor can
appear as the alternative to -wave superconductor{--}the prime proposal to
realize two-dimensional (2D) Kitaev model for topological superconductors
(TSCs) hosting Majorana flat edge mode (MFEM). A general minimal Hamiltonian
suitable for magnet/superconductor heterostructures reveals robust MFEM within
the gap of Shiba bands due to the emergence of an effective ``"-type
-wave pairing, spatially localized at the edges of a 2D magnetic domain of
spin-spiral. We finally verify this concept by considering Mn (Cr) monolayer
grown on a -wave superconducting substrate, Nb(110) under strain (Nb(001)).
In both 2D cases, the antiferromagnetic spin-spiral solutions exhibit robust
MFEM at certain domain edges that is beyond the scope of the trivial extension
of 1D spin-chain model in 2D. This approach, particularly when the MFEM appears
in the TSC phase for such heterostructure materials, offers a perspective to
extend the realm of the TSC in 2D.Comment: This is the published versio
Collating and validating indigenous and local knowledge to apply multiple knowledge systems to an environmental challenge: A case-study of pollinators in India
There is an important role for indigenous and local knowledge in a Multiple Evidence Base to make decisions about the use of biodiversity and its management. This is important both to ensure that the knowledge base is complete (comprising both scientific and local knowledge) and to facilitate participation in the decision making process. We present a novel method to gather evidence in which we used a peer-to-peer validation process among farmers that we suggest is analogous to scientific peer review. We used a case-study approach to trial the process focussing on pollinator decline in India. Pollinator decline is a critical challenge for which there is a growing evidence base, however, this is not the case world–wide. In the state of Orissa, India, there are no validated scientific studies that record historical pollinator abundance, therefore local knowledge can contribute substantially and may indeed be the principle component of the available knowledge base. Our aim was to collate and validate local knowledge in preparation for integration with scientific knowledge from other regions, for the purpose of producing a Multiple Evidence Base to develop conservation strategies for pollinators. Farmers reported that vegetable crop yields were declining in many areas of Orissa and that the abundance of important insect crop pollinators has declined sharply across the study area in the last 10–25 years, particularly Apis cerana, Amegilla sp. and Xylocopa sp. Key pollinators for commonly grown crops were identified; both Apris cerana and Xylocopa sp. were ranked highly as pollinators by farmer participants. Crop yield declines were attributed to soil quality, water management, pests, climate change, overuse of chemical inputs and lack of agronomic expertise. Pollinator declines were attributed to the quantity and number of pesticides used. Farmers suggested that fewer pesticides, more natural habitat and the introduction of hives would support pollinator populations. This process of knowledge creation was supported by participants, which led to this paper being co-authored by both scientists and farmers
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Wild insect diversity increases inter-annual stability in global crop pollinator communities.
While an increasing number of studies indicate that range, diversity and abundance of many wild pollinators has declined, the global area of pollinator-dependent crops has significantly increased over the last few decades. Crop pollination studies to date, have mainly focused on either identifying different guilds pollinating various crops, or on factors driving spatial changes and turnover observed in these communities. The mechanisms driving temporal stability for ecosystem functioning and services, however, remain poorly understood. Our study quantifies temporal variability observed in crop pollinators in 21 different crops across multiple years at a global scale. Using data from 43 studies from six continents, we show that (i) higher pollinator diversity confers greater inter-annual stability in pollinator communities, (ii) temporal variation observed in pollinator abundance is primarily driven by the three most dominant species, and (iii) crops in tropical regions demonstrate higher inter-annual variability in pollinator species richness than crops in temperate regions. We highlight the importance of recognising wild pollinator diversity in agricultural landscapes to stabilize pollinator persistence across years to protect both biodiversity and crop pollination services. Short-term agricultural management practices aimed at dominant species for stabilising pollination services need to be considered alongside longer-term conservation goals focussed on maintaining and facilitating biodiversity to confer ecological stability