Mechanisms Affecting Population Density in Fragmented Habitat

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

doi:10.5751/es-01265-100107

Cited by 56 publications

(43 citation statements)

References 33 publications

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“…In fact, it has been described that ladybirds often do not remain long in any given location, but instead appear to move frequently between sites and habitats throughout the breeding season (Evans, 2003). Anyway, our data help develop an understanding of the dispersal behaviour of ladybirds that remain in the landscape, and may be useful for modelling the influence of dispersal on the abundance and distribution of coccinellids in fragmented landscapes (Tischendorf et al, 2005).…”

Section: Discussionmentioning

confidence: 99%

Ladybird (Coleoptera: Coccinellidae) dispersal in experimental fragmented alfalfa landscapes

Grez¹,

Zaviezo²,

Ríos³

2005

Eur. J. Entomol.

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Abstract. Habitat fragmentation may affect the dispersal behaviour of individuals across the landscape. If there is a high boundary contrast between the remaining fragments and the matrix, individuals should tend to stay inside the fragments, but the configuration of the landscape, i.e. the level of fragmentation and isolation distance between fragments, may modulate this. To test these ideas, we made several mark-recapture experiments with the ladybird Eriopis connexa (Germ.) in manipulated alfalfa model landscapes (30 × 30 m). Specifically we evaluated (i) ladybird movement and permanence in alfalfa and bare ground areas, (ii) how they move across fragment/matrix boundaries, (iii) how their movement between fragments within a landscape is affected by fragmentation level and isolation distance, and (iv) how their permanence in the landscape is affected by fragmentation level and isolation distance. The fragmented alfalfa landscapes had a constant level of habitat loss (84%), but varied in the level of habitat fragmentation (4 or 16 fragments), and isolation distance between fragments (2 or 6 m). We also sampled aphid abundance in the different landscapes through time. We found that ladybirds stay longer and displace less in alfalfa than on bare ground, and that they move less from the alfalfa fragments to the neighbouring bare ground matrix than vice versa. At the landscape level, ladybirds had a higher inter-fragment movement when fragments were closer, they tended to remain in less fragmented landscapes, regardless of their isolation distance. Aphid abundance increased in time, but it was similar in all landscapes. Ladybird movement within fragments, in the matrix and in the boundary between both habitats explains why ladybirds concentrate within alfalfa fragments. However, their dispersal movements at the landscape level do not reflect the higher abundance sometimes found for several species of ladybirds in more fragmented landscapes. At this larger scale, other mechanisms may have a stronger influence in determining the abundance of ladybirds.

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Section: Discussionmentioning

confidence: 99%

Ladybird (Coleoptera: Coccinellidae) dispersal in experimental fragmented alfalfa landscapes

Grez¹,

Zaviezo²,

Ríos³

2005

Eur. J. Entomol.

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“…Instead, ecologists often rely on expert opinion or ad hoc methods of specifying connectivity values, even in important applied settings (Adriaensen et al 2003, Beier et al 2008, Zeller et al 2012). In addition, no methods are available for simultaneously estimating population density and connectivity parameters, in spite of theory predicting interacting effects of density and connectivity on population viability (Tischendorf et al 2005). …”

Section: Introductionmentioning

confidence: 99%

Spatial capture–recapture models for jointly estimating population density and landscape connectivity

Royle¹,

Chandler²,

Gazenski³

et al. 2013

Ecology

102

174

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Abstract. Population size and landscape connectivity are key determinants of population viability, yet no methods exist for simultaneously estimating density and connectivity parameters. Recently developed spatial capture-recapture (SCR) models provide a framework for estimating density of animal populations but thus far have not been used to study connectivity. Rather, all applications of SCR models have used encounter probability models based on the Euclidean distance between traps and animal activity centers, which implies that home ranges are stationary, symmetric, and unaffected by landscape structure. In this paper we devise encounter probability models based on ''ecological distance,'' i.e., the least-cost path between traps and activity centers, which is a function of both Euclidean distance and animal movement behavior in resistant landscapes. We integrate least-cost path models into a likelihood-based estimation scheme for spatial capture-recapture models in order to estimate population density and parameters of the least-cost encounter probability model. Therefore, it is possible to make explicit inferences about animal density, distribution, and landscape connectivity as it relates to animal movement from standard capture-recapture data. Furthermore, a simulation study demonstrated that ignoring landscape connectivity can result in negatively biased density estimators under the naive SCR model.

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“…In previous studies using similar alfalfa landscapes that varied in fragmentation per se and isolation at high levels of habitat loss (84%), there was a weak but positive effect of habitat fragmentation on the abundance of H. convergens and H. variegata, but only when fragments were 2 m apart and not when they were 6 m apart (i.e., as in the landscapes considered in this study) (Grez et al, 2004a). The variable responses of species to landscape configuration may depend upon species dispersal behaviour and demography (Tischendorf et al, 2005). More mobile species may track more efficiently the landscapes discontinuities than less mobile species, and their densities should be less affected by habitat fragmentation (Ricketts, 2001;Ewers & Didham, 2006).…”

Section: Discussionmentioning

confidence: 99%

“…Because more fragmented landscapes contain more habitat edge per area of habitat than less fragmented or continuous habitats, immigrants arriving in the matrix will be more likely to encounter adjacent habitat in the more fragmented landscapes (Bowman et al, 2002;Grez et al, 2004a). Emigration may also be enhanced by increased habitat edge, but this will depend on resource availability, dispersal mode, and boundary crossing probability (Kareiva, 1982;Banks & Yasenak, 2003;Tischendorf et al, 2005). Also, social interactions in some organisms, such as crabs and rodents, may result in high densities or species richness in smaller fragments (Collins & Barret, 1997;Wolff et al, 1997;Caley et al, 2001).…”

Section: Discussionmentioning

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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Mechanisms Affecting Population Density in Fragmented Habitat

Cited by 56 publications

References 33 publications

Ladybird (Coleoptera: Coccinellidae) dispersal in experimental fragmented alfalfa landscapes

Ladybird (Coleoptera: Coccinellidae) dispersal in experimental fragmented alfalfa landscapes

Spatial capture–recapture models for jointly estimating population density and landscape connectivity

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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