Annual estimates of occupancy for bryophytes, lichens and invertebrates in the UK, 1970–2015

Here, we determine annual estimates of occupancy and species trends for 5,293 UK bryophytes, lichens, and invertebrates, providing national scale information on UK biodiversity change for 31 taxonomic groups for the time period 1970 to 2015. The dataset was produced through the application of a Bayesian occupancy modelling framework to species occurrence records supplied by 29 national recording schemes or societies (n = 24,118,549 records). In the UK, annual measures of species status from fine scale data (e.g. 1 × 1 km) had previously been limited to a few taxa for which structured monitoring data are available, mainly birds, butterflies, bats and a subset of moth species. By using an occupancy modelling framework designed for use with relatively low recording intensity data, we have been able to estimate species trends and generate annual estimates of occupancy for taxa where annual trend estimates and status were previously limited or unknown at this scale. These data broaden our knowledge of UK biodiversity and can be used to investigate variation in and drivers of biodiversity change

Responses of phytophagous insects to a changing flora

Changes in the distribution of the British flora have been well documented (Preston et al., 2002; Braithwaite et al., 2006). One might expect phytophagous insects, particularly host plant specialists, to respond to such changes, as they are dependent on plants for their food supply. However, large-scale assessments of the changes in distribution of insect taxa are rare, even though insects represent a major component of terrestrial biodiversity and there has been a long tradition of biological recording. In particular, the absence for most insect groups of repeat national surveys has limited the extent to which we can compare surveys at different time-periods. However, changes in the ranges of many species over time can be identified from the available sequence of records, and current research is providing more rigorous techniques to extract trend information from continuous records (Hill, 2011). Furthermore, phytophagous insects may respond to changes in the availability of food plants growing as agricultural crops, in parks and gardens and in the wild, whereas botanical studies usually provide information solely on wild populations. Assessment of insect population trends in relation to plant distributions are also complicated by the fact that other aspects of the environment have been changing simultaneously. We will review emerging evidence from analyses of insect distribution datasets in relation to changes in the distribution of plants alongside the effects of climate change, the arrival of non-native species and habitat modification. Lepidoptera are the most extensively studied group of insects in the UK and as such provide a wealth of evidence highlighting changes in the geographical range, abundance, phenology and biotic interactions of species. Some species of Lepidoptera have switched hosts in recent years. The Brown Argus butterfly, Aricia agestis, has expanded its distribution northwards in the UK, spreading away from calcareous grassland habitats (where its main host plant is Helianthemum nummularium) into other types of grassland, where its larvae feed on Geraniaceae species (mainly Geranium molle and Erodium cicutarium). This change in host plant association has been facilitated by warming climate rather than changes to the distribution of plants. The arrival and spread of non-native plants has been one of the most noticeable changes to the UK landscape. There are many documented examples of the arrival and establishment of non-native phytophagous insects which are dependent on these non-native plants. The planthopper, Prokelisia marginata, on cordgrass, Spartina anglica, provides one such example. There are a number of conifer-specialists that have recently arrived in Britain and are feeding on conifers within parks and gardens. The western conifer seed bug Leptoglossus occidentalis, native to North America, arrived in Britain in 2008. Some native insects are also benefiting from the proliferation of conifers in gardens. Eremocoris fenestratus was historically associated with junipers in the Chilterns and had not been recorded since the 1960s until 2010 when specimens of this bug were found on garden cypresses in London. Here we provide examples of changes in the distribution patterns of phytophagous insects in response to changing flora and interactions with environmental change. We conclude that change in the distribution of host plants is simply one of several simultaneous environmental changes to which phytophagous insects are responding. Braithwaite, M.E., Ellis, R.W. & Preston, C.D. 2006. Change in the British Flora 1987-2004. Botanical Society of the British Isles, London. Hill, M.O. 2011. Local frequency as a key to interpreting species occurrence data when recording effort is not known. Methods in Ecology and Evolution, 3, 195-205. Preston, C.D., Pearman, D.A. & Dines, T.D., eds 2002. New atlas of the British & Irish flora. Oxford University Press, Oxford

The role of ecological interactions in determining species ranges and range changes

Climate has been widely regarded as the main determinant of the geographical distribution of species. Biotic interactions between co-occurring species, however, are an important additional influence. We review the importance of interactions with food and nectar plants (as resources) in determining the distribution of phytophagous and pollinating insects (as consumers). We use biological recording datasets for seven taxonomic groups to quantify the relationship between the geographical distributions within Britain of 1265 phytophagous insects and their associated food plants, representing 9128 interactions in total. We find a consistent pattern across taxonomic groups in that individual phytophagous insect species rarely utilize the full range of their food plants and the relationship between the range sizes of insects and their food plants is not a simple linear one. For a small selection of phytophagous species where data are available, we highlight an association between changes in range and interactions with associated food plant species. Climate-driven range expansion may be constrained through disruption of trophic relationships between phytophagous insects and their food plants if they respond differently to abiotic drivers. By contrast, range expansion may be facilitated by temporary escape from natural enemies and/or exploitation of novel food plants that enable a broader set of habitats to be utilized. In a changing environment, some existing interactions will be disrupted but opportunities for novel interactions will also emerge, producing new assemblages and changes in distributions that will be dynamic yet hard to predict