Tag Archives: Urbanization

Conserving insect assemblages in urban landscapes: accounting for species-specific responses and imperfect detection

This post is a about a new paper in the Journal of Insect Conservation.

Using the El Maresme shire (north-eastern Spain) as the study area and heteropteran bugs as model organisms, my colleagues (Marta Goula & Amy Hahs) and I set out to explore the effects of urbanization on insects.

An illustration of the brachypterous form of Ischnodemus sabuleti (Fallén, 1826) by Aleksandar Stojanović.
An illustration of the brachypterous form of Ischnodemus sabuleti (Fallén, 1826) by Aleksandar Stojanović.

I was especially impressed by the large diversity of bugs species that we found in our survey. The field work yielded 142 different species of heteropteran bugs. Since the heteropteran bug gamma diversity of El Maresme is known to be  323 species1, we can estimate that our study collected detection and occupancy data for almost 45% of the heteropteran bug species known to the region. Among these species was the ash-grey leafbug Piesma maculatum (Laporte, 1833), a species that had not been seen in El Maresme in almost 100 years (the first and only previously known record was published by A. Sánchez  in 19202). Also among the collected species was Ischnodemus sabuleti (Fallén, 1826), which represented the first record in El Maresme of the family Blissidae.

During field work I also had the opportunity to photograph some beautiful pentatomid species, such as Nezara viridula (Linnaeus, 1758) and Carpocoris fuscispinus (Boheman, 1851).

A mating pair of the green stinkbug Nezara viridula (Linnaeus, 1758)
A mating pair of the green stinkbug Nezara viridula (Linnaeus, 1758)

But what did we actually do?

We used a hierarchical occupancy-detection model to estimate the community and species-specific responses of heteropteran bugs to a gradient of urbanization. Our results indicated that heteropteran bug species richness and community-level occupancy are predicted to decrease along the urbanization gradient.

Occ by urb (CL)
Predicted relationships between heteropteran bug community level occupancy and urbanization. The black solid line represents the mean, while the black dashed lines represent the 95 % credible interval. The grey lines represent the full range of uncertainty associated with the mean response.

Likewise, our species-specific results showed that approximately two-thirds of all the heteropteran bug species experienced a strong negative response to urbanization. Given these results, we argue that many species are potentially at risk of local extinction as cities and towns in this region grow and expand in the future.

Figure 5
Predicted relationships between mean heteropteran bug species-specific probabilities of occurrence and urbanization for the (a) whole community, (b) species showing the strongest mean negative response and the widest credible intervals not overlapping zero, and (c) species showing the weakest mean negative response and the narrowest credible intervals not overlapping zero.

Some other species, however, showed a weak negative response to urbanization, indicating that they might be common urban species that do well in cities and towns regardless of the level of surrounding urban disturbance.  Among these species were the rhopalid Liorhyssus hyalinus (Fabricius, 1794), the plant bug Lygus pratensis (Linnaeus, 1758) and the oxycarenid Oxycarenus lavaterae (Fabricius, 1787), all of them well-known generalist pests. And, interestingly, among these common urban species we also found generalist pest control agents such as the pirate bug Orius laevigatus (Fieber, 1860).

Although we provide quantitative evidence for the relationship between insects and urbanization, these remain correlative rather than causative. So, in the paper we argued that the potential fine-scaled mechanisms driving the observed patterns may be better understood by investigating, for example, the vegetation structural complexity of herbaceous ruderal urban ecosystems or looking more closely at how predatory occurrence relates to prey availability.

Thanks for your interest, and if you would like to find more about the paper, click here for a non-formatted version or drop me an e-mail at luis.mata(at)rmit.edu.au and I will send you an author’s copy.

1 Mata L. 2013. Heteroptera ecology, biodiversity and conservation. University of Barcelona, PhD thesis

Sánchez A. 1920. Càtaleg dels insects del Museu pertanyents al ordre Hemíptera. Publicaciones de la Junta de Ciencias Naturales de Barcelona 3: 225-258.