Diversity and structure of Metrosideros polymorpha canopy arthropod communities across space and time

Global biodiversity is under pressure from climate change, habitat fragmentation and other anthropogenic change, and our ability to predict biodiversity responses to change requires a better understanding of the processes that drive diversity and structure local communities. However, quantifying these processes has proven to be challenging for multiple reasons; diversity is multidimensional, and both diversity and the processes that generate it vary across scale. In this dissertation, I examine temporal and spatial patterns in community structure to test hypotheses about the drivers of local diversity and composition in communities of varying age, focusing on arthropod communities associated with the native tree Metrosideros polymorpha on the Hawaiian Islands. Analysis of Hemiptera (true bug) communities reveals a temporal pattern in community structure, where young substrate communities were variable in species composition and beta dispersion decreased with substrate age, indicating convergence. However, substrate age did not correlate with community dissimilarity in a directional way. Similarly, geographic distance did not correlate with compositional dissimilarity, suggesting a lack of dispersal limitation. I confirmed this result by examining connections between arthropod communities in a historically fragmented ‘kīpuka’ landscape, using species-area relationships and graph theory analyses. Finally, if canopy arthropods are dispersive and differences in species composition across sites are not driven by substrate age, local habitat characteristics may influence species composition. I determined the role of local beta diversity and identified habitat characteristics regarding forest structure and host leaf traits that are strong drivers of beta diversity and species composition. Then, to further explore local habitat drivers I examined forests with high intraspecific variation in co-occurring Metrosideros. In this hybrid zone, insect life history traits shape species’ response to intraspecific variation in host plant characteristics, highlighting the importance of including dimensions of biodiversity beyond taxonomic diversity. Together, these results demonstrate the importance of local habitat conditions for canopy arthropods, suggest that canopy arthropod communities are highly connected and that substrate age plays a limited role in determining local arthropod communities. Such insights into biodiversity and plant-insect interactions across temporal and spatial scale are integral to understanding and conserving our natural world

A novel mechanism for grazing lawn formation: large herbivore-induced modification of the plant-soil water balance

1. Large herbivores play a key role in creating spatial heterogeneity through the formation of grazing lawns. Recent research suggests that the currently accepted nutrient-based theory on the formation of these grazing lawns cannot universally explain their formation in all ecosystems where they are found. 2. We developed and investigated an alternative hypothesis on grazing lawn formation and maintenance based on herbivore effects on the plant–soil water balance. We propose that large herbivores change the soil water balance in grazing lawns through defoliation and soil compaction, causing a shift in vegetation composition towards a drought-tolerant plant community. 3. Investigating this idea in a tropical savanna, we indeed found profound differences in grazing lawn soil properties and water balance. In particular, defoliation increased soil temperatures and potential evaporation rates while soil compaction increased bulk density and decreased water infiltration rates, especially on fine-textured soils. Soil moisture was therefore generally much lower in grazing lawns than in adjacent bunch grass areas. 4. Furthermore, we found that grazing lawn species show drought-tolerant traits, with higher leaf sodium levels, suggesting evolutionary adaptation to these herbivore-induced dry conditions. However, leaf water potentials did not differ between grazing lawn and bunch grass species. 5. Synthesis. This study shows that large herbivores might form grazing lawns through previously underestimated effects on water balance. Thus, future studies on large herbivore effects on vegetation should increasingly focus on additional pathways of soil compaction and defoliation. While nutrient-based processes driving grazing lawn formation may operate during the wet season in savannas, we suggest that water balance-based processes are additionally important during the dry season

A novel mechanism for grazing lawn formation: large herbivore-induced modification of the plant-soil water balance

Veldhuis MP, Howison RA, Fokkema R, Tielens E, Olff H. A novel mechanism for grazing lawn formation: large herbivore-induced modification of the plant-soil water balance. Journal of Ecology. 2014;102(6):1506-1517

Data from: A novel mechanism for grazing lawn formation: large herbivore-induced modification of the plant-soil water balance

1. Large herbivores play a key-role in creating spatial heterogeneity through the formation of grazing lawns. Recent research suggests that the currently accepted nutrient-based theory on the formation of these grazing lawns cannot universally explain their formation in all ecosystems where they are found. 2. We developed and investigated an alternative hypothesis on grazing lawn formation and maintenance based on herbivore effects on the plant-soil water balance. We propose that large herbivores change the soil water balance in grazing lawns through defoliation and soil compaction, causing a shift in vegetation composition towards a drought tolerant plant community. 3. Investigating this idea in a tropical savanna, we indeed found profound differences in grazing lawn soil properties and water balance. In particular, defoliation increased soil temperatures and potential evaporation rates while soil compaction increased bulk density and decreased water infiltration rates, especially on fine-textured soils. Soil moisture was therefore generally much lower in grazing lawns than in adjacent bunch grass areas. 4. Furthermore, we found that grazing lawn species show drought-tolerant traits, with higher leaf sodium levels, suggesting evolutionary adaptation to these herbivore-induced dry conditions. However, leaf water potentials did not differ between grazing lawn and bunch grass species. 5. Synthesis: This study shows that large herbivores might form grazing lawns through previously underestimated effects on water balance. Thus, future studies on large herbivore effects on vegetation should increasingly focus on additional pathways of soil compaction and defoliation. While nutrient-based processes driving grazing lawn formation may operate during the wet season in savannas, we suggest that water balance-based processes are additionally important during the dry season

Data from: A novel mechanism for grazing lawn formation: Large herbivore-induced modification of the plant-soil water balance

This study shows that large herbivores might form grazing lawns through previously underestimated effects on water balance. Thus, future studies on large herbivore effects on vegetation should increasingly focus on additional pathways of soil compaction and defoliation. While nutrient‐based processes driving grazing lawn formation may operate during the wet season in savannas, we suggest that water balance‐based processes are additionally important during the dry season. Data and R scripts available

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Expansion of Distant Marketing of Vegetables in Bangladesh : A case study on Losmanpur village in Sherpur district

The distant marketing of vegetables has been developed in many places of the country because of the price differences among the regions. This research aims to explore the expansion process of the distant marketing developed at a village in Bangladesh. The historical data collected through a field survey at Losmanpur village in Sherpur district is used for this study. The expansion of distant marketing is divided into 3 stages: the launching of distant marketing stage during 1983 and 1985, the adaptive distant marketing stage during 1986 and 1993 and the extensive distant marketing stage since 1994 thereafter. The market at the initial stage was limited to only one season in one market of Dhaka city that has been expanded for whole the year to many other markets of other cities, too. This research has identified the factors influencing for the expansion of the distant marketing. The vegetable business requires less capital because the traders collect vegetables mostly on credit from the farms. The success factor of the credit-sale is the trust between the farmers and traders. The development of rice millings in Sherpur district has an indirect effect on the expansion of vegetable marketing because the vegetable has been carried as the extra load of rice trucks. The price information was available from the traders or truck drivers coming back to the locality. The expansion of telephone since the early 1990’s and the mobile phone since the late 1990’s has facilitated for receiving the update market price. The relation among the traders was friendly at the early stage of marketing and subsequently become collusive and competitive for increasing the number of traders. The farmers of the study village have expanded vegetable farming from 66 ha to 194 ha during 1996 and 2004 because of the gradual increase of demand

Long‐term analysis of persistence and size of swallow and martin roosts in the US Great Lakes

Abstract In this study, we combined a machine learning pipeline and human supervision to identify and label swallow and martin roost locations on data captured from 2000 to 2020 by 12 Weather Surveillance Radars in the Great Lakes region of the US. We employed radar theory to extract the number of birds in each roost detected by our technique. With these data, we set out to investigate whether roosts formed consistently in the same geographic area over two decades and whether consistency was also predictive of roost size. We used a clustering algorithm to group individual roost locations into 104 high‐density regions and extracted the number of years when each of these regions was used by birds to roost. In addition, we calculated the overall population size and analyzed the daily roost size distributions. Our results support the hypothesis that more persistent roosts are also gathering more birds, but we found that on average, most individuals congregate in roosts of smaller size. Given the concentrations and consistency of roosting of swallows and martins in specific areas throughout the Great Lakes, future changes in these patterns should be monitored because they may have important ecosystem and conservation implications