Alvin J. Helden

Urban biodiversity: comparison of insect assemblages on native and non-native trees

Trees are thought to be important for supporting urban biodiversity. However tree species differ considerably in the numbers of invertebrates they support, with potential consequences for higher trophic groups such as birds. In this study the influence of native and non-native trees on the abundance of insects (Hemiptera) and the incidence of insectivorous birds (Paridae) were investigated in the southern English town of Bracknell. The number and species of tree were recorded from each of 17 roundabout and parkland sites. Tree beating was used to sample arboreal Hemiptera and Paridae were recorded either with point counts and transect walks, depending on the size of the site. Due to the great variation between tree species, there was no overall significant difference in species richness or abundance of Hemiptera between native and non-native tree species. However, individual native trees had more species and individuals than non-natives. The proportion of native trees at Bracknell sites was positively related to the abundance of both Hemiptera and the number of Paridae observed. The consequences of vegetation type for insect abundance indicates that in order to sustain and enhance urban biodiversity, careful consideration needs to be given to species of trees present in urban areas.

The role of grassland sward islets in the distribution of arthropods in cattle pastures.

1. It is well documented that cattle reduce their grazing activity in the vicinity of cattle dung, which gives rise to distinct patches, or islets as they have been termed, of longer sward. The influence of such islets on pasture utilisation and agronomic performance has been widely studied, but very little information is available concerning their influence on grassland biodiversity.

Magic Roundabouts? Teaching Conservation in Schools and Universities.

Pitfall trap sampling of Carabid beetle species on roundabouts in Bracknell, Berkshire, was used to assess the biodiversity of this taxon by its use as an indicator. The aim of the study was to discover the role of traffic islands in the provision of refugia for invertebrate fauna in fragmented urban habitats. Sampling was performed on 15 roundabouts where a total of 24 species were recorded during four trapping periods over a total of 10 days. The resulting asymptotic curves indicated that the total number of species present on all but two of the sites had been represented in the samples taken. There was found to be a positive correlation between the area of the islands and the number of ground beetle species and between the log of the area and the number of individuals found. The log/log relationship between the area of the islands and the number of species was significant. The total abundance of the beetles present was also positively and significantly correlated with roundabout area when both variables were logged. The number of habitats on the islands was positively correlated with the total abundance and species richness. The relationship between species, area and habitat was also positively and significantly correlated. In conclusion, it is obvious that roundabouts of large area with higher numbers of habitat types are greater in Carabid beetle diversity than small, sparsely vegetated roundabouts. Thus, roundabouts can promote the maintenance of biodiversity in fragmented urban habitats.We present this study as an example of a simple method that could be used or easily adapted for educational use, and suggest how some of the perceived problems in its use may be overcome. We discuss how such a study could be useful in illustrating concepts such as biodiversity and species richness, and some of the factors that influence it, as well as demonstrating the level of biodiversity that can be found in urban environments.

Phenotypic plasticity and interpopulation differences in life history traits of Armadillidium vulgare (Isopoda:Oniscidae)

The hypothesis that the balance of trade-offs between survivorship, growth and reproductive allocation in the terrestrial isopod Armadillidium vulgare will change when resource input is increased has been investigated experimentally. When the quality of food available was increased, by adding a mixture of litter from herbaceous dicotyledonous plants to a background low-quality food of dead grasses, survivorship was found to be the most phenotypically plastic trait, increasing by 168%. Growth rates increased by 99% but reproductive allocation by only 21%. In the field, members of a population from a site with more high-quality food grew more than twice as fast as those from a site where less high-quality food was available. The population from the site with higher food availability, contrary to predictions from the laboratory study, did not survive as well as that from the site with less available high-quality food. This may be because the site that is more favourable for growth has a more stressful physical environment due to much bigger temperature fluctuations, which are known to be an important cause of mortality in this species. When individuals from both populations were reared under controlled laboratory conditions, both the parental and F1 generations from the poor growth environment survived better than those from the good growth habitat. However, even when given an excess of high-quality food those from the poor growth environment continued to grow more slowly and had a lower reproductive allocation than those from the site with higher food availability. We conclude that microevolutionary changes may have occurred in the balance of resource allocation between survivorship, growth and reproductive allocation, to favour higher survivorship during the longer prereproductive period at the site where growth to the threshold size for reproduction takes longer.

Experimental sward islets: the effect of dung and fertilisation on Hemiptera and Araneae

Abstract.  1. Cattle avoid grazing around their dung. This pattern persists after the decomposition of the initial dung patch leading to the formation of taller grass patches, termed islets. It is known that islets hold a disproportionate amount of the arthropods in grazed grasslands.

The influence of conservation field margins in intensively managed grazing land on communities of five arthropod trophic groups

Abstract.  1. Arthropods, a major component of functional biodiversity within agro‐ecosystems, contribute to sustainability through processes including nutrient cycling and pest control. Extensively managed field margins can help protect this functional biodiversity by providing habitat for beneficial species.

First extant records of mermithid nematode parasitism of Auchenorrhyncha in Europe

Parasitic nematodes of the family Mermithidae were found within four specimens of Auchenorrhyncha from two families (Cicadellidae and Delphacidae). This appears to be the the first extant example of mermithid parasitism of Auchenorrhyncha in Europe. The insect hosts were collected from agricultural grassland field margins at three locations in Ireland during a farmland biodiversity study in 2007.

Field-based grassland management for cirl buntings (Emberiza cirlus L.) and its effect on plant- and leafhoppers (Hemiptera: Auchenorrhyncha).

The cirl bunting (Emberiza cirlus L.) has been the subject of targeted and successful conservation efforts based on agri‐environment schemes (AES) in the UK since 1993. Recent work has suggested that although focused on a single species, there have been wider biodiversity benefits for plants and some invertebrates. In this study we investigated whether a similar pattern could be found for the Auchenorrhyncha (plant‐ and leafhoppers) within agricultural grasslands, where they form an important component of the herbivore community. Sweep netting was used to sample Auchenorrhyncha from AES pastures, on which no pesticide or fertiliser inputs are allowed, and from conventionally grazed and cut (silage) fields at 25 locations in south Devon UK, during 2008. Generalised linear mixed models and non‐metric multidimensional scaling were used to model abundance, species density, and community structure. AES fields had the highest abundance, followed by conventionally grazed and then cut fields. The same pattern occurred for species density, although there was no significant difference between conventionally grazed and cut fields. There was no difference in community structure between field types. Number of plant species, sward age, and nitrogen input were important covariates of field type, suggesting that the limitations on inputs resulting from AES are the likely drivers of the observed differences. The results add to the evidence base that suggests that increased agricultural intensity is inversely related to invertebrate biodiversity. They also provide evidence that AES designed for the cirl bunting have provided wider biodiversity benefits.

Tim R. New: Insect conservation and urban environments

Having tackled agricultural ecosystems, in a previous book (New 2005), Tim New has now synthesised our present understanding of insect conservation in that other most human impacted of environments, urban areas. Such a book is of course very much needed given the worldwide context of continued rapid human population growth requiring ever more land for towns and cities. The book is not unduly negative or pessimistic but realistic, seeking to show, with examples from throughout the world, what we know about human impacts on urban insects and how solutions can be found to enable us to live more harmoniously with our insect neighbours. This very readable book consists of 11 chapters, beginning with consideration of the characteristics of urban areas and how their changing nature modifies ecosystems at a broad level. The first chapter also sets the scene, with regard to the history of urban insect research. The following chapters give an overview of the now considerable literature on urban insect ecology and conservation, with each focusing on a different aspect, such as the widely used approach of urban–rural gradient studies, impacts on communities and species, threats and the provision of suitable habitats for urban insects. Within each chapter the author uses specific examples of studies to explain the relevant issues and the text is supported well by many wellchosen tables, diagrams and photographs. One of the major themes running through the earlier chapters of the book is that many of the ecological processes and conservation strategies in urban areas are largely the same as those found in other ecosystems. So, for example, urban insect communities are modified through habitat fragmentation, loss and modification, with the associated issue of extinction debt. However, compounding these problems is the fixation that many people have for the tidiness of urban green spaces, which typified by the saproxylic insects, limits habitat suitability for many species. In chapter seven, the author identifies a range of other threats that are relatively more influential in urban ecosystems than elsewhere. Specifically the urban heat island effect, artificial lighting, the effects of vehicle traffic, and how predators of insects can interact with these issues, such as bats hunting around street lights. There is also a whole chapter on the impacts of alien species, which although of course occurring in rural areas as well, are most widely introduced and spread within urban environments. This chapter emphasises that the relationships of insects with alien species are a complex mix of positive and negative, such as the Chilean needle grass (Nassella neesiana) that is considered a noxious weed and yet provides an important larval food source for the native, endangered golden sun-moth (Synemon plana) in Australia. In three of the later chapters the focus shifts to habitats. The author describes the range of habitat types available to insects, from fragments of pre-urban forest and urban rivers that predate urban expansion, through traditional urban green spaces such as parks and domestic gardens, to specific attempts to increase green infrastructure such as green roofs and walls. Issues of habitat restoration and the improvement of the design of projects with functions not directly related to conservation, including storm water management systems and golf courses, are also covered. It is in these chapters that the author draws out one of the important lessons we need to learn for the future. We must improve the links and communication between & Alvin. J. Helden alvin.helden@anglia.ac.uk

The response of sward-dwelling arthropod communities to reduced grassland management intensity in pastures

Abstract We compared arthropod taxon richness, diversity and community structure of two replicated grassland husbandry experiments to investigate effects of reduced management intensity, as measured by nutrient input levels (390, 224 and 0 kg/ha per year N in one experiment, and 225 and 88 kg/ha per year N in another). Suction sampling was used to collect Araneae, Coleoptera, Hemiptera and Hymenoptera, with Araneae and Coleoptera also sampled with pitfall trapping. Univariate analyses found no significant differences in abundance and species density between treatments. However, with multivariate analysis, there were significant differences in arthropod community structure between treatments in both experiments. Reducing N input and associated stocking rates, as targeted by agri-environment schemes, can significantly alter arthropod communities but without increasing the number of species present. Other approaches that may be necessary to achieve substantial enhancement of sward arthropod biodiversity are suggested.