Does variation in census area confound density comparisons?

Does variation in census area confound density comparisons? 1. Estimates of density are not always independent of the area over which populations are censused. Instead, lower densities tend to be recorded for species when they are censused over larger areas. This may have serious implications for both intra‐ and interspecific comparisons of density, with relevance to such issues as conservation prioritization and management strategies, because differences in density may simply result from differences in census areas. 2. Here, we use long‐term population census data for British birds in the period 1968–91, drawn from the Common Birds Census (CBC), to examine relationships between density and census area within species, and the consequences of these relationships for intraspecific and interspecific density comparisons. 3. Most British bird species exhibit statistically significant negative relationships between density and census area. We used these relationships to standardize mean density estimates for all species to a common census area. These area‐adjusted estimates were usually very similar to geometric mean density estimates calculated without reference to census area. 4. For a subset of species recorded from a large number (> 30) of census sites in each year in the period 1968–91, we used intraspecific density–area relationships for each year to standardize mean density estimates to a common census area in all years. Again, the area‐adjusted estimates for each year were usually very similar to the simple geometric mean density estimates calculated for the species in the same year. 5. These results are encouraging, but are certainly a consequence of the relatively limited range of census areas used here, and the fact that the mean census area varies little across species, or across years within species. Moreover, those species occupying few sites are the most likely to have area‐biased densities, but are the species for which area‐correction will be most difficult. 6. Overall, the results suggest that past analyses conducted using the CBC data are unlikely to have been seriously confounded by variation in census area. Nevertheless, they do highlight that the effects of census area will require consideration by anyone planning to measure or use densities for comparative purposes either within or among species. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Journal of Applied Ecology Wiley

Does variation in census area confound density comparisons?

Loading next page...
 
/lp/wiley/does-variation-in-census-area-confound-density-comparisons-v8UDQq7VBi
Publisher
Wiley
Copyright
Copyright © 1999 Wiley Subscription Services, Inc., A Wiley Company
ISSN
0021-8901
eISSN
1365-2664
D.O.I.
10.1046/j.1365-2664.1999.00401.x
Publisher site
See Article on Publisher Site

Abstract

1. Estimates of density are not always independent of the area over which populations are censused. Instead, lower densities tend to be recorded for species when they are censused over larger areas. This may have serious implications for both intra‐ and interspecific comparisons of density, with relevance to such issues as conservation prioritization and management strategies, because differences in density may simply result from differences in census areas. 2. Here, we use long‐term population census data for British birds in the period 1968–91, drawn from the Common Birds Census (CBC), to examine relationships between density and census area within species, and the consequences of these relationships for intraspecific and interspecific density comparisons. 3. Most British bird species exhibit statistically significant negative relationships between density and census area. We used these relationships to standardize mean density estimates for all species to a common census area. These area‐adjusted estimates were usually very similar to geometric mean density estimates calculated without reference to census area. 4. For a subset of species recorded from a large number (> 30) of census sites in each year in the period 1968–91, we used intraspecific density–area relationships for each year to standardize mean density estimates to a common census area in all years. Again, the area‐adjusted estimates for each year were usually very similar to the simple geometric mean density estimates calculated for the species in the same year. 5. These results are encouraging, but are certainly a consequence of the relatively limited range of census areas used here, and the fact that the mean census area varies little across species, or across years within species. Moreover, those species occupying few sites are the most likely to have area‐biased densities, but are the species for which area‐correction will be most difficult. 6. Overall, the results suggest that past analyses conducted using the CBC data are unlikely to have been seriously confounded by variation in census area. Nevertheless, they do highlight that the effects of census area will require consideration by anyone planning to measure or use densities for comparative purposes either within or among species.

Journal

Journal of Applied EcologyWiley

Published: Apr 1, 1999

References

You’re reading a free preview. Subscribe to read the entire article.


DeepDyve is your
personal research library

It’s your single place to instantly
discover and read the research
that matters to you.

Enjoy affordable access to
over 18 million articles from more than
15,000 peer-reviewed journals.

All for just $49/month

Explore the DeepDyve Library

Search

Query the DeepDyve database, plus search all of PubMed and Google Scholar seamlessly

Organize

Save any article or search result from DeepDyve, PubMed, and Google Scholar... all in one place.

Access

Get unlimited, online access to over 18 million full-text articles from more than 15,000 scientific journals.

Your journals are on DeepDyve

Read from thousands of the leading scholarly journals from SpringerNature, Elsevier, Wiley-Blackwell, Oxford University Press and more.

All the latest content is available, no embargo periods.

See the journals in your area

DeepDyve

Freelancer

DeepDyve

Pro

Price

FREE

$49/month
$360/year

Save searches from
Google Scholar,
PubMed

Create folders to
organize your research

Export folders, citations

Read DeepDyve articles

Abstract access only

Unlimited access to over
18 million full-text articles

Print

20 pages / month

PDF Discount

20% off