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1

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Response of generalist and specialist insect herbivores to landscape spatial structure (1997)

Jonsen, Ian D. ; Fahrig, Lenore

Springer

Landscape ecology 12 (1997), S. 185-197

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ISSN: 1572-9761

Keywords: alfalfa ; diversity ; farmland ; habitat patch ; arthropods ; isolation ; landscape pattern ; leafhoppers ; scale ; weevils

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract The purpose of this study was to investigate the effect ofchanges in landscape pattern on generalist and specialistinsects. We did this by comparing the species richness andabundance of generalist and specialist herbivorous insects inalfalfa (Medicago sativa, L.) fields on 26 agriculturallandscapes that differed in spatial structure. The insects werefrom the families Curculionidae (Coleoptera), weevils, andCicadellidae (Auchennorhyncha), leafhoppers. We hypothesized that: (1) generalist richness and abundancewould be highest in landscapes with high diversity(Shannon-Wiener); (2) specialist richness and abundance would behighest in landscapes with (i) high percent cover alfalfa and(ii) low mean inter-patch distance. We tested for these effectsafter controlling for the patch-level effects of field size,field age, frequency of disturbance and vegetation texture. The important findings of the study are: (1) generalist richness andabundance increased with increasing landscape diversity and (2)isolation (percent cover alfalfa in the landscape and/or meaninter-patch distance) does not affect specialist insects. Theseresults are significant because they indicate that bothgeneralist and specialist insects may move over much largerdistances than previously thought. This is one of the firststudies to demonstrate a large scale effect of spatial structureon insects across a broad range of landscapes.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1023/A:1007961006232

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2

Electronic Resource

How should we measure landscape connectivity? (2000)

Tischendorf, Lutz ; Fahrig, Lenore

Springer

Landscape ecology 15 (2000), S. 633-641

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ISSN: 1572-9761

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract The methods for measuring landscape connectivity have never been compared or tested for their responses to habitat fragmentation. We simulated movement, mortality and boundary reactions across a wide range of landscape structures to analyze the response of landscape connectivity measures to habitat fragmentation. Landscape connectivity was measured as either dispersal success or search time, based on immigration into all habitat patches in the landscape. Both measures indicated higher connectivity in more fragmented landscapes, a potential for problematic conclusions for conservation plans. We introduce cell immigration as a new measure for landscape connectivity. Cell immigration is the rate of immigration into equal-sized habitat cells in the landscape. It includes both within- and between-patch movement, and shows a negative response to habitat fragmentation. This complies with intuition and existing theoretical work. This method for measuring connectivity is highly robust to reductions in sample size (i.e., number of habitat cells included in the estimate), and we hypothesize that it therefore should be amenable to use in empirical studies. The connectivity measures were weakly correlated to each other and are therefore generally not comparable. We also tested immigration into a single patch as an index of connectivity by comparing it to cell immigration over the landscape. This is essentially a comparison between patch-scale and landscape-scale measurement, and revealed some potential for patch immigration to predict connectivity at the landscape scale. However, this relationship depends on the size of the single patch, the dispersal characteristics of the species, and the amount of habitat in the landscape. We conclude that the response of connectivity measures to habitat fragmentation should be understood before deriving conclusions for conservation management.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1023/A:1008177324187

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3

Electronic Resource

The advantage of long-distance clonal spreading in highly disturbed habitats (1994)

Fahrig, Lenore ; Coffin, Debra P. ; Lauenroth, William K. ; [et al.]

Springer

Evolutionary ecology 8 (1994), S. 172-187

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ISSN: 1573-8477

Keywords: disturbance ; long-distance clonal spreading ; life history ; grazing ; overwash ; barrier island ; short-grass steppe ; spatial simulation model

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Summary Classical theory states that cover of annual plants should increase relative to perennials as disturbance frequency increases. However, it has been suggested that long-distance clonal spreading can allow some perennial plants to survive in highly disturbed areas by quickly spreading into disturbed patches. To evaluate these hypotheses, we analysed data of plant distributions in two different ecosystems, a barrier island and a short-grass steppe. The disturbances studied were sand deposition during storms (overwash) on the barrier island and grazing by cattle in the short-grass steppe. In each case the disturbance frequency varied over the ecosystem; we categorized different areas in terms of their disturbance frequencies. All plant species in each area were categorized as one of four plant life forms (1) annual or biennial, (2) herbaceous perennial without long-distance clonal spreading (3) herbaceous perennial with long-distance clonal spreading (i.e guerilla form) and (4) woody plant. Percentage cover of each plant life form in each disturbance frequency category was calculated. In both ecosystems, (1) there was an increase in the relative cover of annuals as one moved from areas of low to moderate disturbance frequencies, but then a decrease in cover of annuals as one moved into the areas of highest disturbance frequency and (2) the guerilla forms showed the greatest relative increase in cover from moderately to highly disturbed areas. The combination of two factors can explain this pattern: (1) long-distance clonal spreading effectively reduces the time to colonization of recently disturbed sites and (2) effects of the disturbances in these two systems are probably more severe for seeds than for stems. We illustrate these effects using a spatially explicit simulation model of the population dynamics of plants in a disturbed landscape.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF01238248

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4

Electronic Resource

Effect of Habitat Patch Characteristics on Abundance and Diversity of Insects in an Agricultural Landscape (1998)

Fahrig, Lenore ; Jonsen, Ian

Springer

Ecosystems 1 (1998), S. 197-205

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ISSN: 1435-0629

Keywords: Key words: agro-ecosystem; patch size; resource concentration hypothesis; patch isolation; metapopulation; patch age; intermediate disturbance hypothesis; insect density; insect richness.

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: ABSTRACT The objective of this study was to test for general effects of patch size, patch isolation, disturbance frequency, and patch life span, on density and diversity of organisms. We sampled predominantly herbivorous insects in 31 alfalfa fields that varied in size, isolation, frequency of disturbance by cutting, and age (number of years planted in alfalfa). Effects on insect relative density and diversity were examined at three taxonomic levels: all insects, eight separate orders, and six legume-specialist weevil species. We found that (a) more isolated alfalfa fields had higher overall insect richness, (b) fields with higher disturbance frequency had lower overall insect richness, and (c) fields of intermediate age had highest insect richness. In some cases these patterns were reflected at lower taxonomic levels, but in many cases they were not. These results are important because they indicate that, although we cannot simultaneously tailor a landscape for each of thousands of species, we may be able to produce desired effects at a more general level.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s100219900015

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Increasing crop heterogeneity enhances multitrophic diversity across agricultural regions (2019)

Sirami, Clélia ; Gross, Nicolas ; Baillod, Aliette Bosem ; [et al.]

National Academy of Sciences

In: PNAS - Proceedings of the National Academy of Sciences of the United States of America. 2019; 116(33): 16442-16447. Published 2019 Jul 29. doi: 10.1073/pnas.1906419116.

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Publication Date: 2019-07-29

Description: Agricultural landscape homogenization has detrimental effects on biodiversity and key ecosystem services. Increasing agricultural landscape heterogeneity by increasing seminatural cover can help to mitigate biodiversity loss. However, the amount of seminatural cover is generally low and difficult to increase in many intensively managed agricultural landscapes. We hypothesized that increasing the heterogeneity of the crop mosaic itself (hereafter “crop heterogeneity”) can also have positive effects on biodiversity. In 8 contrasting regions of Europe and North America, we selected 435 landscapes along independent gradients of crop diversity and mean field size. Within each landscape, we selected 3 sampling sites in 1, 2, or 3 crop types. We sampled 7 taxa (plants, bees, butterflies, hoverflies, carabids, spiders, and birds) and calculated a synthetic index of multitrophic diversity at the landscape level. Increasing crop heterogeneity was more beneficial for multitrophic diversity than increasing seminatural cover. For instance, the effect of decreasing mean field size from 5 to 2.8 ha was as strong as the effect of increasing seminatural cover from 0.5 to 11%. Decreasing mean field size benefited multitrophic diversity even in the absence of seminatural vegetation between fields. Increasing the number of crop types sampled had a positive effect on landscape-level multitrophic diversity. However, the effect of increasing crop diversity in the landscape surrounding fields sampled depended on the amount of seminatural cover. Our study provides large-scale, multitrophic, cross-regional evidence that increasing crop heterogeneity can be an effective way to increase biodiversity in agricultural landscapes without taking land out of agricultural production.

Print ISSN: 0027-8424

Electronic ISSN: 1091-6490

Topics: Biology , Medicine , Natural Sciences in General

Published by National Academy of Sciences

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Different Anuran Species Show Different Relationships to Agricultural Intensity (2016)

Koumaris, Alex ; Fahrig, Lenore

Springer

In: Wetlands. 2016; 36(4): 731-744. Published 2016 Jun 07. doi: 10.1007/s13157-016-0781-4.

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Publication Date: 2016-06-07

Print ISSN: 0277-5212

Electronic ISSN: 1943-6246

Topics: Biology

Published by Springer

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Effects of a recent wildfire and clearcuts on ground-dwelling boreal forest spider assemblages (2005)

Larrivée, Maxim ; Fahrig, Lenore ; Drapeau, Pierre

Canadian Science Publishing

In: Canadian Journal of Forest Research. 2005; 35(11): 2575-2588. Published 2005 Nov 01. doi: 10.1139/x05-169.

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Publication Date: 2005-11-01

Description: Ground-dwelling spider (Araneae) assemblages were compared between recent clearcuts and burned black spruce (Picea mariana (Mill.) BSP) forests. Spiders were sampled using pitfall traps placed in 6 recently burned sites, 6 recently clear-cut sites, and 6 undisturbed sites in eastern Quebec, Canada. A total of 2935 individuals from 95 spider species were identified. Catch rates for hunting spiders were significantly higher in the clear-cut stands than in the burned stands, but between-stand species turnover of hunting spiders was twice as high in the burned stands as in the clear-cut stands. Web-building spiders had similar catch rates in the three stand types, but had the highest species turnover and gamma diversity in the undisturbed sites. Correspondence analysis showed that the composition of the spider assemblages varied among the three types of stands. Spider assemblages found in clearcuts were associated with environmental variables reflecting dry, open, disturbed forest floor, while assemblages found in burned stands were correlated with high percentages of shrub cover and dried mosslichen substrate and deeper litter. We conclude that ground-living spider assemblages in boreal forest respond very differently to clearcuts and fires and we suggest modifications to present forestry practices to create disturbances that are more similar to wildfires.

Print ISSN: 0045-5067

Electronic ISSN: 1208-6037

Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Published by Canadian Science Publishing

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