The effects of urbanization on bird and carabid beetle communities

Urbanization is proceeding rapidly in many parts of the world with important consequences for biodiversity. However, it is unclear whether different taxa respond similarly to urbanization. To date, the vast majority of studies in urban areas have been carried out on birds. Thus, birds have become a de facto indicator taxon for urbanization due to their inherent appeal, conspicuousness, mostly diurnal habits and well-known natural history, and the extensive development of research techniques with which to study them. In terms of understanding and mitigating the effects of urbanization on biodiversity, it is important to determine whether the responses of birds correlate with the responses of other taxa.

 

We compare the responses of breeding birds and carabid beetles to urbanization to determine whether the emerging generalizations of the effects of extreme levels of urbanization on birds (declines in total species richness and the richness of specialist species, increases in total abundance and the abundances of native generalist and introduced species, and community simplification, including increasing similarity) also apply to ground beetles.

 

Birds displayed strong declines in diversity, compositional changes, and community simplification in response to increasing housing density (see the results below and Gagné and Fahrig (2011) for more information). Forest and introduced species of birds and beetles responded similarly to increasing housing density, but responses of overall diversity and open-habitat species richness and patterns of community simplification differed between birds and beetles.

 

To better understand and mitigate the effects of urbanization on biodiversity, we suggest that, in addition to the responses of birds, future research should focus on the responses  of other taxa in the urban matrix.

 

The effects of housing density on measures of breeding bird and carabid beetle diversity. The mean value of each response variable +/- one standard error is presented for each site category. Different lowercase letters indicate significant pairwise differences between site categories for each response variable. * P < 0.05; ** P < 0.001.

 

Taxon Response variable F3,12 Adjusted R2 Housing density site category
Forested(n = 4) Exurban(n = 4) Suburban(n = 4) Urban(n = 4)
Birds Species richness 23.64** 0.82 29.00 +/- 2.74a 29.50 +/- 1.76a 20.00 +/- 1.92b 12.00 +/- 1.08c
Simpson’s index 54.39** 0.91 0.93 +/- 0.01a 0.94 +/- 0.01a 0.91 +/- 0.01a 0.75 +/- 0.02b
Fisher’s α 36.30** 0.88 15.46 +/- 2.27a 15.28 +/- 1.22a 7.54 +/- 0.79b 3.47 +/- 0.44c
Beetles Open-habitat species richness 4.90* 0.44 2.25 +/- 0.95a 6.75 +/- 2.59ab 11.75 +/- 1.70b 11.00 +/- 2.27b

 

The abundance (a) and species richness (b) of forest birds and carabid beetles and the abundance of introduced birds and carabid beetles (c) in Forested (F), Exurban (E), Suburban (S) and Urban (U) sites. Dark gray bars represent forest interior birds in (a) and (b) and introduced birds in (c). Light gray bars represent forest edge birds and open bars represent carabid beetles. Different lowercase letters above bars indicate significant pairwise differences between site categories for each taxon and habitat affinity group.

a)

a

b)

b

 

c)

c

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Distance biplots showing the locations of bird (a) and carabid beetle (b) species scores from redundancy analyses with housing density as a predictor. The centroids of the Forested (F), Exurban (E), Suburban (S) and Urban (U) housing density categories are also shown.

a)

biplot a

 

b)

biplot b

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The k-dominance curves of birds and carabid beetles. Each curve represents the data collected at a single site. A community is considered to be dominated by a few species to a greater degree than another community if its dominance curve lies above and never intersects that of the other community.

k-dominance birds       k-dominance beetles

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Additive partitioning of bird and carabid beetle diversity in housing density categories. Dark gray bars are the average station species richness (α1), light gray bars are the average species richness among stations (β1) and open bars are the average species richness among sites (β2). F, Forested; E, Exurban; S, Suburban; U, Urban.

additive partitioning birds   additive partitioning beetles

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Non-metric multidimensional scalings of bird and carabid beetle community data collected in Forested (F), Exurban (E), Suburban (S), and Urban (U) sites.

non-metric birds   non-metric beetles

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The Kulczynski distance between pairs of Forested (F), Exurban (E), Suburban (S) and Urban (U) sites. The Kulczynski distance between two sites was calculated by summing species abundance minima and dividing this value by each site’s total abundance. One minus the average of these two values was the distance between the two sites. Gray bars represent the distances between bird communities and open bars represent those between carabid beetle communities. Different lowercase letters above bars indicate significant pairwise differences between site categories for each taxon.

Kulczynski

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