SummaryThere is considerable concern over declines in insect pollinator communities and potential impacts on the pollination of crops and wildflowers [1][2][3][4] . Among the multiple pressures facing pollinators [2][3][4] , decreasing floral resources due to habitat loss and degradation has been suggested as a key contributing factor 2-8 . However, a lack of quantitative data has hampered testing for historical changes in floral resources. Here we show that overall floral rewards can be estimated at a national scale by combining vegetation surveys and direct nectar measurements. We find evidence for substantial losses in nectar resources in England and Wales between the 1930s and 1970s; however, total nectar provision in Great Britain as a whole had stabilised by 1978, and increased from 1998 to 2007. These findings concur with trends in pollinator diversity, which declined in the mid-20th century 9 but stabilised more recently 10 . The diversity of nectar sources declined from 1978 to 1990 but stabilised thereafter at low levels, with four plant species accounting for over 50% of national nectar provision in 2007. Calcareous grassland, broadleaved woodland and neutral grassland are the habitats that produce the greatest amount of nectar per unit area from the most diverse sources, whereas arable land is the poorest in both respects. While agrienvironment schemes add resources to arable landscapes, their national contribution is low. Due to

A numerical technique for assembly of ecological communities of Lotka-Volterra form is described. The technique is based upon a global criterion for coexistence of species known as permanence. This provides a relatively fast and accurate method to determine the sequence of communities that develops when species are drawn sequentially and in an arbitrary order from a regional pool of species. Steps in the assembly sequence that cannot be resolved by this method are determined by numerical integration. The results are as follows.( 1) At each step in an assembly sequence, a species that succeeds in invading when rare persists in the resulting community even if one or more of the resident species becomes extinct. (2) Assembly sequences are terminated with a community that is uninvadable by any of the remaining species from the pool. The number of these endpoints is small, even when the species pool is large. (3) In some cases, the final community cannot be reassembled from the species left in it; other species, which are absent at the end, are needed for the endpoint to be reached. (4) Invasion resistance builds up in three stages during an assembly sequence. Over much of the sequence, invasion resistance shows little if any increase; during this period, species composition continues to change until the sequence happens to land on an endpoint. (5) Communities assembled from large species pools are more resistant to invasion than those assembled from small species pools.

The states to which multispecies communities can tend has been an important issue in ecology, but one in which rather little progress has been made at a theoretical level through lack of a tractable global theory of the dynamics. This paper explores the use of a global theory called "permanence" that indicates whether the boundary of a phase space is a repellor to orbits in the phase space. The theory is used to try to identify, at a qualitative level, the states to which solutions tend in the phase space of an arbitrary pool of species. We define a "permanent state" of the pool as a subset of the species that is permanent in its own right and uninvadable by any other species from the pool. A simple assembly rule for communities that stems from this is that no permanent state can be a subset of another. Data on coexistence of drosophilid species and also on that of cuckoodoves, although incomplete, are consistent with this rule. A method is given for finding the permanent states of pools of species with Latka-Volterra dynamics. Some properties of permanent states are illustrated by means of numerical examples from regional pools of species generated with Latka-Volterra dynamics. These examples show three kinds of dynamics: a single permanent state, two or more alternative permanent states in which none are subsets of others, and an absence of any permanent states. The statistical distribution of these outcomes in pools of four and five species indicates that a single permanent state is the most likely one to occur, but that alternative states become more probable as the number of interactions among species increases. The implications of these results for understanding and modelling the process of succession driven by population dynamics are discussed.

Change in land cover is thought to be one of the key drivers of pollinator declines, and yet there is a dearth of studies exploring the relationships between historical changes in land cover and shifts in pollinator communities. Here, we explore, for the first time, land cover changes in England over more than 80 years, and relate them to concurrent shifts in bee and wasp species richness and community composition. Using historical data from 14 sites across four counties, we quantify the key land cover changes within and around these sites and estimate the changes in richness and composition of pollinators. Land cover changes within sites, as well as changes within a 1 km radius outside the sites, have significant effects on richness and composition of bee and wasp species, with changes in edge habitats between major land classes also having a key influence. Our results highlight not just the land cover changes that may be detrimental to pollinator communities, but also provide an insight into how increases in habitat diversity may benefit species diversity, and could thus help inform policy and practice for future land management.

Land cover mapping of large areas is challenging due to the significant volume of satellite data to acquire and process, as well as the lack of spatial continuity due to cloud cover. Temporal aggregation—the use of metrics (i.e., mean or median) derived from satellite data over a period of time—is an approach that benefits from recent increases in the frequency of free satellite data acquisition and cloud-computing power. This enables the efficient use of multi-temporal data and the exploitation of cloud-gap filling techniques for land cover mapping. Here, we provide the first formal comparison of the accuracy between land cover maps created with temporal aggregation of Sentinel-1 (S1), Sentinel-2 (S2), and Landsat-8 (L8) data from one-year and test whether this method matches the accuracy of traditional approaches. Thirty-two datasets were created for Wales by applying automated cloud-masking and temporally aggregating data over different time intervals, using Google Earth Engine. Manually processed S2 data was used for comparison using a traditional two-date composite approach. Supervised classifications were created, and their accuracy was assessed using field-based data. Temporal aggregation only matched the accuracy of the traditional two-date composite approach (77.9%) when an optimal combination of optical and radar data was used (76.5%). Combined datasets (S1, S2 or S1, S2, and L8) outperformed single-sensor datasets, while datasets based on spectral indices obtained the lowest levels of accuracy. The analysis of cloud cover showed that to ensure at least one cloud-free pixel per time interval, a maximum of two intervals per year for temporal aggregation were possible with L8, while three or four intervals could be used for S2. This study demonstrates that temporal aggregation is a promising tool for integrating large amounts of data in an efficient way and that it can compensate for the lower quality of automatic image selection and cloud masking. It also shows that combining data from different sensors can improve classification accuracy. However, this study highlights the need for identifying optimal combinations of satellite data and aggregation parameters in order to match the accuracy of manually selected and processed image composites.