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Influence of landscape structure and human modifications on insect biomass and bat foraging activity in an urban landscape.

Threlfall CG, Law B, Banks PB - PLoS ONE (2012)

Bottom Line: We found that insect biomass was at least an order of magnitude greater within suburban landscapes in bushland and backyard elements located on the most fertile shale influenced geologies (both p<0.001) compared to nutrient poor sandstone landscapes.These were ambient temperature (positive), housing density (negative) and the percent of fertile shale geologies (positive) in the landscape; however variation in insect biomass did not directly explain bat foraging activity.We suggest that prey may be unavailable to bats in highly urbanized areas if these areas are avoided by many species, suggesting that reduced feeding activity may reflect under-use of urban habitats by bats.

View Article: PubMed Central - PubMed

Affiliation: Evolution and Ecology Research Centre, School of Biological, Earth and Environmental Sciences, University of New South Wales, Sydney, New South Wales, Australia. caragh.threlfall@unimelb.edu.au

ABSTRACT
Urban landscapes are often located in biologically diverse, productive regions. As such, urbanization may have dramatic consequences for this diversity, largely due to changes in the structure and function of urban communities. We examined the influence of landscape productivity (indexed by geology), housing density and vegetation clearing on the spatial distribution of nocturnal insect biomass and the foraging activity of insectivorous bats in the urban landscape of Sydney, Australia. Nocturnal insect biomass (g) and bat foraging activity were sampled from 113 sites representing backyard, open space, bushland and riparian landscape elements, across urban, suburban and vegetated landscapes within 60 km of Sydney's Central Business District. We found that insect biomass was at least an order of magnitude greater within suburban landscapes in bushland and backyard elements located on the most fertile shale influenced geologies (both p<0.001) compared to nutrient poor sandstone landscapes. Similarly, the feeding activity of bats was greatest in bushland, and riparian elements within suburbs on fertile geologies (p = 0.039). Regression tree analysis indicated that the same three variables explained the major proportion of the variation in insect biomass and bat foraging activity. These were ambient temperature (positive), housing density (negative) and the percent of fertile shale geologies (positive) in the landscape; however variation in insect biomass did not directly explain bat foraging activity. We suggest that prey may be unavailable to bats in highly urbanized areas if these areas are avoided by many species, suggesting that reduced feeding activity may reflect under-use of urban habitats by bats. Restoration activities to improve ecological function and maintain the activity of a diversity of bat species should focus on maintaining and restoring bushland and riparian habitat, particularly in areas with fertile geology as these were key bat foraging habitats.

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Nocturnal insect biomass (g) for each landscape element across landscape categories.(A) total biomass; (B) moth biomass; (C) beetle biomass; and (D) other biomass. The data are log (x+0.01 transformed) Least Squares means (± standard error), after adjusting for average nightly temperature. Results of planned contrasts (which combine categories) are included in the text.
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pone-0038800-g002: Nocturnal insect biomass (g) for each landscape element across landscape categories.(A) total biomass; (B) moth biomass; (C) beetle biomass; and (D) other biomass. The data are log (x+0.01 transformed) Least Squares means (± standard error), after adjusting for average nightly temperature. Results of planned contrasts (which combine categories) are included in the text.

Mentions: The ANCOVA of total insect biomass revealed a significant landscape category by element interaction (Table S1, Fig. 2A). Insect biomass also significantly increased with increasing nightly temperature (Table S1), and varied among the replicate landscape blocks (Table S1). A priori contrasts to explore the interaction term revealed that within the suburban landscapes, shale backyards had insect biomass 36 times greater than transition backyards (t2, 68 = 3.1, P = 0.003), but did not differ compared to sandstone backyards (t2, 68 = 1.76, P = 0.08). Shale bushland also had insect biomass which was two orders of magnitude greater than sandstone bushland (t2, 68 = 3.54, P = 0.0007), but did not differ compared to transition bushland (t2, 68 = 1.53, P = 0.13). Open space and riparian elements did not differ significantly between the suburban landscapes (all P-values>0.05). Open space elements within vegetated landscapes had significantly lower insect biomass than within suburban landscapes (combined across all geologies) (t2, 68 = −2.33, P = 0.02), but not urban landscapes (t2, 68 = −1.06, P = 0.29). Insect biomass in riparian elements within vegetated landscapes was not significantly different to urban landscapes (t2, 68 = 1.70, P = 0.09), or suburban landscapes (t2, 68 = 1.63, P = 0.11). Backyard and bushland elements did not differ significantly between vegetated and suburban, or vegetated and urban landscapes (all P-values>0.05, Fig. 2A). Moth, beetle and ‘other’ biomass did not significantly vary between landscape categories or elements (Table S1, Fig. 2B–D). However, moth biomass varied among replicate blocks, as did beetle and the ‘others’ biomass, along with increasing temperature (Table S1).


Influence of landscape structure and human modifications on insect biomass and bat foraging activity in an urban landscape.

Threlfall CG, Law B, Banks PB - PLoS ONE (2012)

Nocturnal insect biomass (g) for each landscape element across landscape categories.(A) total biomass; (B) moth biomass; (C) beetle biomass; and (D) other biomass. The data are log (x+0.01 transformed) Least Squares means (± standard error), after adjusting for average nightly temperature. Results of planned contrasts (which combine categories) are included in the text.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3369849&req=5

pone-0038800-g002: Nocturnal insect biomass (g) for each landscape element across landscape categories.(A) total biomass; (B) moth biomass; (C) beetle biomass; and (D) other biomass. The data are log (x+0.01 transformed) Least Squares means (± standard error), after adjusting for average nightly temperature. Results of planned contrasts (which combine categories) are included in the text.
Mentions: The ANCOVA of total insect biomass revealed a significant landscape category by element interaction (Table S1, Fig. 2A). Insect biomass also significantly increased with increasing nightly temperature (Table S1), and varied among the replicate landscape blocks (Table S1). A priori contrasts to explore the interaction term revealed that within the suburban landscapes, shale backyards had insect biomass 36 times greater than transition backyards (t2, 68 = 3.1, P = 0.003), but did not differ compared to sandstone backyards (t2, 68 = 1.76, P = 0.08). Shale bushland also had insect biomass which was two orders of magnitude greater than sandstone bushland (t2, 68 = 3.54, P = 0.0007), but did not differ compared to transition bushland (t2, 68 = 1.53, P = 0.13). Open space and riparian elements did not differ significantly between the suburban landscapes (all P-values>0.05). Open space elements within vegetated landscapes had significantly lower insect biomass than within suburban landscapes (combined across all geologies) (t2, 68 = −2.33, P = 0.02), but not urban landscapes (t2, 68 = −1.06, P = 0.29). Insect biomass in riparian elements within vegetated landscapes was not significantly different to urban landscapes (t2, 68 = 1.70, P = 0.09), or suburban landscapes (t2, 68 = 1.63, P = 0.11). Backyard and bushland elements did not differ significantly between vegetated and suburban, or vegetated and urban landscapes (all P-values>0.05, Fig. 2A). Moth, beetle and ‘other’ biomass did not significantly vary between landscape categories or elements (Table S1, Fig. 2B–D). However, moth biomass varied among replicate blocks, as did beetle and the ‘others’ biomass, along with increasing temperature (Table S1).

Bottom Line: We found that insect biomass was at least an order of magnitude greater within suburban landscapes in bushland and backyard elements located on the most fertile shale influenced geologies (both p<0.001) compared to nutrient poor sandstone landscapes.These were ambient temperature (positive), housing density (negative) and the percent of fertile shale geologies (positive) in the landscape; however variation in insect biomass did not directly explain bat foraging activity.We suggest that prey may be unavailable to bats in highly urbanized areas if these areas are avoided by many species, suggesting that reduced feeding activity may reflect under-use of urban habitats by bats.

View Article: PubMed Central - PubMed

Affiliation: Evolution and Ecology Research Centre, School of Biological, Earth and Environmental Sciences, University of New South Wales, Sydney, New South Wales, Australia. caragh.threlfall@unimelb.edu.au

ABSTRACT
Urban landscapes are often located in biologically diverse, productive regions. As such, urbanization may have dramatic consequences for this diversity, largely due to changes in the structure and function of urban communities. We examined the influence of landscape productivity (indexed by geology), housing density and vegetation clearing on the spatial distribution of nocturnal insect biomass and the foraging activity of insectivorous bats in the urban landscape of Sydney, Australia. Nocturnal insect biomass (g) and bat foraging activity were sampled from 113 sites representing backyard, open space, bushland and riparian landscape elements, across urban, suburban and vegetated landscapes within 60 km of Sydney's Central Business District. We found that insect biomass was at least an order of magnitude greater within suburban landscapes in bushland and backyard elements located on the most fertile shale influenced geologies (both p<0.001) compared to nutrient poor sandstone landscapes. Similarly, the feeding activity of bats was greatest in bushland, and riparian elements within suburbs on fertile geologies (p = 0.039). Regression tree analysis indicated that the same three variables explained the major proportion of the variation in insect biomass and bat foraging activity. These were ambient temperature (positive), housing density (negative) and the percent of fertile shale geologies (positive) in the landscape; however variation in insect biomass did not directly explain bat foraging activity. We suggest that prey may be unavailable to bats in highly urbanized areas if these areas are avoided by many species, suggesting that reduced feeding activity may reflect under-use of urban habitats by bats. Restoration activities to improve ecological function and maintain the activity of a diversity of bat species should focus on maintaining and restoring bushland and riparian habitat, particularly in areas with fertile geology as these were key bat foraging habitats.

Show MeSH
Related in: MedlinePlus