A transient, positive effect of habitat fragmentation on insect population densities

Grez, Audrey A.; Zaviezo, Tania; Tischendorf, Lutz; Fahrig, Lenore

doi:10.1007/s00442-004-1670-8

Cited by 71 publications

(73 citation statements)

References 29 publications

(45 reference statements)

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“…Some studies have shown a ''crowding effect'' that is a relatively positive effect of fragmentation on insect population density (Debinski and Holt 2000). After habitat fragmentation, insect populations may disperse to adjacent fragments, resulting in a local increase in population density (Debinski andHolt 2000, Grez et al 2010) in small fragments that have a larger edge proportion (Fagan et al 1999, Grez et al 2010. Our results suggest a ''crowding effect'' of gall wasp community, in the remaining habitat as small fragments and isolated oaks.…”

Section: Fragmentation and Host Plant Qualitymentioning

confidence: 99%

Gall wasp community response to fragmentation of oak tree species: importance of fragment size and isolated trees

Maldonado-López

Cuevas‐Reyes

Stone³

et al. 2015

Ecosphere

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We explore the impact of habitat fragmentation on interactions between keystone resources of forest trees—oaks, genus Quercus (Fagaceae)—and an associated radiation of specialist cynipid gall wasps. Habitat fragmentation is predicted to have bottom‐up impacts on cynipid communities through impacts on host plant quality (plant vigor hypothesis). We explored the bottom‐up impacts on cynipid communities of habitat fragment size, fragment edge effects and presence of isolated oaks. We quantified temporal and spatial variation of leaves produced in the canopy to quantify plant vigor, and surveyed cynipid gall species abundance and richness over three years using 15 permanent forest patches and 25 isolated oaks in a fragmented oak woodland landscape in central Mexico. Cynipid gall abundance and species richness were higher in isolated oaks and small woodland fragments than in larger ones. Cynipid abundance and species richness were also higher along fragment edges in comparison with fragment interiors. This contrasts with patterns observed in other taxa. In addition, host plant quality was higher in isolated trees, in smaller fragments and along fragment edges. We therefore hypothesize that observed patterns in cynipid abundance and species richness are driven by changes in host plant quality due to forest fragmentation. Our data represent a baseline for longer‐term monitoring of fragmentation effects at a landscape scale. Further work is required to explore alternative potential explanations for observed patterns, including the estimation of potential top‐down impacts of fragmentation mediated by natural enemies.

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Section: Fragmentation and Host Plant Qualitymentioning

confidence: 99%

Gall wasp community response to fragmentation of oak tree species: importance of fragment size and isolated trees

Maldonado-López

Cuevas‐Reyes

Stone³

et al. 2015

Ecosphere

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“…This array allowed analysis at five spatial scales, consisting of 1, 3, 9, 27, and 81 plants. Although habitat fragmentation, between‐patch distance and system area all may affect the dispersal behavior and distribution of ladybeetles (Grez, Zaviezo, & Rios, 2005; Grez, Zaviezo, Tischendorf, & Fahrig, 2004; Holt, 1985; Zaviezo, Grez, Estades, & Perez, 2006), we did not seek to investigate their isolated effects. Instead, the fractal design of our experiment allowed a systematic increase in system area, average between‐patch distance, and total patch size with increasing spatial scale and has been regarded as one neutral way to simulate complex habitats (Halley et al., 2004).…”

Section: Methodsmentioning

confidence: 99%

Predator–prey interactions in a ladybeetle–aphid system depend on spatial scale

Lin

Pennings

2018

Ecology and Evolution

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The outcome of species interactions may manifest differently at different spatial scales; therefore, our interpretation of observed interactions will depend on the scale at which observations are made. For example, in ladybeetle–aphid systems, the results from small‐scale cage experiments usually cannot be extrapolated to landscape‐scale field observations. To understand how ladybeetle–aphid interactions change across spatial scales, we evaluated predator–prey interactions in an experimental system. The experimental habitat consisted of 81 potted plants and was manipulated to facilitate analysis across four spatial scales. We also simulated a spatially explicit metacommunity model parallel to the experiment. In the experiment, we found that the negative effect of ladybeetles on aphids decreased with increasing spatial scales. This pattern can be explained by ladybeetles strongly suppressing aphids at small scales, but not colonizing distant patches fast enough to suppress aphids at larger scales. In the experiment, the positive effects of aphids on ladybeetles were strongest at three‐plant scale. In a model scenario where predators did not have demographic dynamics, we found, consistent with the experiment, that both the effects of ladybeetles on aphids and the effects of aphids on ladybeetles decreased with increasing spatial scales. These patterns suggest that dispersal was the primary cause of ladybeetle population dynamics in our experiment: aphids increased ladybeetle numbers at smaller scales because ladybeetles stayed in a patch longer and performed area‐restricted searches after encountering aphids; these behaviors did not affect ladybeetle numbers at larger spatial scales. The parallel experimental and model results illustrate how predator–prey interactions can change across spatial scales, suggesting that our interpretation of observed predator–prey dynamics would differ if observations were made at different scales. This study demonstrates how studying ecological interactions at a range of scales can help link the results of small‐scale ecological experiments to landscape‐scale ecological problems.

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“…Thus, four types of landscapes were created: unfragmented control landscapes or 1F -0% (0% habitat loss, one fragment of alfalfa), 4F -55% (four 10 × 10 m fragments, 55% habitat loss), 4F -84% (four 6 × 6 m fragments, 84% habitat loss), and 16F -84% (sixteen 3 × 3 m fragments, 84% habitat loss). Fragments were separated by 6 m, because this distance reduces the inter-fragment movement of coccinellids within a landscape, and instead enhances emigration from the landscape (i.e., the coccinellids perceive the landscape as more fragmented than landscapes with closer fragments; Grez et al, 2004a;Grez et al, 2005). Such information on dispersal responses does not exist for carabids or aphids.…”

Section: Experimental Landscapesmentioning

confidence: 99%

“…During the summer, insects colonize the crop from nearby hibernation refuges. Therefore, insect population changes shortly after habitat loss and fragmentation should be determined mainly by immigration (Grez et al, 2004a). But during autumn, reproduction, survival, and emigration (to hibernate or seek out more suitable patches) may become the most important demographic mechanisms determining insect densities.…”

Section: Data Analysesmentioning

confidence: 99%

Effects of habitat loss and fragmentation on the abundance and species richness of aphidophagous beetles and aphids in experimental alfalfa landscapes

Grez¹,

Zaviezo²,

Dı́az³

et al. 2008

Eur. J. Entomol.

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Abstract. In agro-ecosystems, habitat loss and fragmentation may alter the assemblage of aphidophagous insects, such as foliarforaging (coccinellids) and ground-foraging predators (carabids), potentially affecting intraguild interactions. We evaluated how habitat loss (0, 55 and 84%), fragmentation (1, 4 and 16 fragments) and their combination affected the abundance and species richness of coccinellids and carabids, and aphid abundance, both in the short-term (summer: December to February) and over a longer time span (autumn: March to May), when different demographic mechanisms may participate. We created four types of 30 × 30 m patches (landscapes) in which alfalfa was grown: Control (1F -0%, 30 × 30 m patch of alfalfa with no fragmentation or habitat loss), 4F -55% (4 alfalfa fragments, with 55% total habitat loss), 4F -84% (4 alfalfa fragments, with 84% total habitat loss), and 16F -84% (16 alfalfa fragments, with 84% total habitat loss). Each landscape type was replicated five times. Insects were sampled by sweep-netting and pitfall traps, from December (summer) to May (autumn). Total abundance and species richness of carabids, in the short-term, was highest in the 16F -84% landscapes. Total abundance of adult coccinellids was similar among landscapes, but at the species level Hyperaspis sphaeridioides, in the short-term, and Adalia bipunctata, in the long-term, had their highest densities in fragments within landscapes with high habitat loss (84%), independently of habitat fragmentation. Species richness in the long-term was higher in the landscapes with 84% habitat loss. Among aphids, in the long term Aphis craccivora was less abundant in landscapes with high habitat loss and fragmentation (16-84%), while Therioaphis trifolii showed the opposite trend. These results suggest that habitat loss and fragmentation may increase the density and diversity of aphidophagous insects, while their effects on aphids are more variable.

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A transient, positive effect of habitat fragmentation on insect population densities

Cited by 71 publications

References 29 publications

Gall wasp community response to fragmentation of oak tree species: importance of fragment size and isolated trees

Gall wasp community response to fragmentation of oak tree species: importance of fragment size and isolated trees

Predator–prey interactions in a ladybeetle–aphid system depend on spatial scale

Effects of habitat loss and fragmentation on the abundance and species richness of aphidophagous beetles and aphids in experimental alfalfa landscapes

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