Scalable Decision Rules for Environmental Impact Studies: Effect Size, Type I, and Type II Errors

The abundance and species richness of mollusc and crab assemblages were examined in a subtropical mangrove forest in Moreton Bay, Queensland, Australia, which has been disturbed and damaged by the construction of a wooden boardwalk and a path. Sections of the forest immediately adjacent to the boardwalk and path were compared with reference areas to determine whether changes to the small-scale structural complexity within the forest affected the benthic fauna. The disturbed area was characterised by having 65-80% fewer pneumatophores, significantly fewer species and individuals of molluscs, but significantly more species and individuals of crabs than the reference areas.The abundance of mangrove pneumatophores and the attached epiphytic algae were manipulated at two sites to determine whether observed differences in these features could account for the differences in the assemblage of molluscs in the disturbed area of the forest compared with reference areas. Five experimental treatments were used: undisturbed controls, pneumatophore removals (abundance reduced by ca. 65%), epiphytic algal removals (algae removed from ca. 65% of pneumatophores), pneumatophore disturbance controls and algal disturbance controls. The experimental reduction of the abundance of mangrove pneumatophores and the associated epiphytic algae led to significant declines (by as much as 83%) in the number of molluscs utilising the substratum in the modified plots. There was no significant difference in the abundance of molluscs in the pneumatophore and algal removal plots suggesting any effect was primarily related to removal of the epiphytic algae from the surface of the pneumatophores.The responses by the biota to the changes in the physical environment demonstrate that even relatively small-scale modifications to the physical structure of subtropical mangrove forests can lead to significant effects on the diversity and abundance of macrobenthic organisms in these habitats. Such modifications have the potential to cause cascading effects at higher trophic levels with a deterioration in the value of these habitats as nursery and feeding grounds. Future efforts at conservation of these estuarine environments must focus on the prevention or reduction of modifications to the physical structure and integrity of the system, rather than just on the prevention of loss of entire patches of habitat.

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“…Gray, 1996) so where effects were significant at P , 0.10 this is also indicated (e.g. Mapstone, 1995).…”

Section: Statistical Analyses Of Sampling Datamentioning

confidence: 61%

Effects of habitat modification in mangroves on the structure of mollusc and crab assemblages

Skilleter

Warren

2000

Journal of Experimental Marine Biology and Ecology

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“…That being said, power increases with sample size. Other carnivore studies have used monitoring criteria of a = b = 0.2 (Barlow et al, 2008), which assumes equal economic, social, political and environmental costs of Type I and II errors (Mapstone, 1995). Using these criteria, annual effort of 12 replicates at each of a simple random sample of P65 sites would offer sufficient power to detect a 50% decline in brown hyaena occupancy in our study area over a 5 year period.…”

Section: Discussionmentioning

confidence: 99%

Brown hyaenas on roads: Estimating carnivore occupancy and abundance using spatially auto-correlated sign survey replicates

Thorn

Green

Bateman

et al. 2011

Biological Conservation

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a b s t r a c tCarnivore survey protocols that properly address spatial sampling and detectability issues are seldom feasible at a landscape-scale. This limits knowledge of large-scale patterns in distribution, abundance and their underlying determinants, hindering conservation of globally threatened carnivore populations. Occupancy analysis of data from logistically efficient sign surveys along consecutive road segments (spatially auto-correlated replicates) offers a potential solution. We adapted and applied this newly-developed method over 62,979 km 2 of human-modified land in South Africa. Our aims were to (1) generate unbiased estimates of brown hyaena occupancy and abundance (2) investigate two suspected determinants of occupancy using a combination of biological and socio-economic sampling techniques, and (3) use simulations to evaluate the effort required for abundance and occupancy estimates with acceptable bias, precision and power. Brown hyaena occupancy was estimated at 0.748 (±SE 0.1), and estimated overall density in agricultural land (0.15/100 km 2 , ±SE 0.08) was an order of magnitude lower than in protected areas. Positive attitudes to carnivores and presence of wildlife farms exerted strong positive effects on occupancy, so changes in these factors may well exert monotonic impacts on local metapopulation status. Producing reliable occupancy and abundance estimates would require P6 replicates and P12 replicates per site respectively. Detecting 50% and 30% declines in brown hyaena occupancy with adequate power would require five annual surveys at P65 sites and P125 sites respectively. Our results suggest that protocols based on spatially auto-correlated sign survey replicates could be used to monitor carnivore populations at large, and possibly even country-wide spatial scales.

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“…To protect against Type II error, we did not adjust for multiple comparisons (Quinn and Keough, 2002;Moran, 2003). Likewise, because the cost of making Type II errors is high, particularly when dealing with management practices that may adversely affect populations, results with 0.10 $ P $ 0.05 were considered marginally significant (Cousens and Marshall, 1987;Mapstone, 1995;Quinn and Keough, 2002).…”

Section: Data Analysesmentioning

confidence: 99%

Short-term Effects of Burning and Disking on Songbird Use of Floodplain Conservation Easements

Benson

Dinsmore

Hohman

2011

The American Midland Naturalist

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Extensive conversion of Midwestern riparian areas for agricultural production has had many consequences including reduced habitat for nesting birds. However, more than 120,000 ha of riparian habitat have been restored in this region through USDA conservation programs. In 2001 and 2002, we assessed songbird responses to burning and disking for management of conservation easements in east-central Iowa. We randomly assigned herbaceous riparian fields to burning and disking treatments and collected data on density and species richness of songbirds in these habitats. Total density of grassland and wetland species and redwinged blackbirds (Agelaius phoeniceus) were reduced by burning in the first and second breeding seasons after burning; common yellowthroat (Geothlypis trichas) density decreased with burning only in the first season. Disking led to increased density of grassland and wetland birds and greater overall avian conservation value on treated relative to untreated fields in the year after treatment. Changes associated with burning and disking treatments were likely related to changes in both vegetation structure and abundance of arthropod food resources. Despite decreased bird densities with burning, fire is a necessary management tool to control woody vegetation. Overall, both burning and disking appear to be effective management practices for maintaining herbaceous riparian habitats for grassland birds. RightsWorks produced by employees of the U.S. Government as part of their official duties are not copyrighted within the U.S. The content of this document is not copyrighted.This article is available at Iowa State University Digital Repository: http://lib.dr.iastate.edu/nrem_pubs/133BioOne sees sustainable scholarly publishing as an inherently collaborative enterprise connecting authors, nonprofit publishers, academic institutions, research libraries, and research funders in the common goal of maximizing access to critical research. Short-term Effects of Burning and Disking on Songbird Use of Floodplain Conservation EasementsAuthor (s) ABSTRACT.-Extensive conversion of Midwestern riparian areas for agricultural production has had many consequences including reduced habitat for nesting birds. However, more than 120,000 ha of riparian habitat have been restored in this region through USDA conservation programs. In 2001 and 2002, we assessed songbird responses to burning and disking for management of conservation easements in east-central Iowa. We randomly assigned herbaceous riparian fields to burning and disking treatments and collected data on density and species richness of songbirds in these habitats. Total density of grassland and wetland species and red-winged blackbirds (Agelaius phoeniceus) were reduced by burning in the first and second breeding seasons after burning; common yellowthroat (Geothlypis trichas) density decreased with burning only in the first season. Disking led to increased density of grassland and wetland birds and greater overall avian conservation value on treated relative ...

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Scalable Decision Rules for Environmental Impact Studies: Effect Size, Type I, and Type II Errors

Cited by 268 publications

References 24 publications

Effects of habitat modification in mangroves on the structure of mollusc and crab assemblages

Effects of habitat modification in mangroves on the structure of mollusc and crab assemblages

Brown hyaenas on roads: Estimating carnivore occupancy and abundance using spatially auto-correlated sign survey replicates

Short-term Effects of Burning and Disking on Songbird Use of Floodplain Conservation Easements

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