Collections also have been useful in determining whether the establishment and early stages of invasion are linked to single or multiple introductions. For example, Russello et al. used genetic evidence obtained from natural history specimens to infer the origin of monk parakeet populations in the USA and to link the invasion success of this species to propagule pressure exerted by the pet trade industry. Voucher specimens are useful for testing evolutionary hypotheses through data gathered from examination of trait and molecular variation. Molecular methods can be used to examine genetic variation of introduced populations and to reconstruct patterns of genetic change over time. For example, Hartley et al. used DNA extracted from vouchers to determine that blow flies were preadapted to rapid evolution in response to organophosphate insecticides. Also, phenotypic changes that occur during the different stages of invasions can be examined using natural history collections. Zangerl and Berenbaum used herbarium specimens to examine changes in phytochemistry of an invasive plant over a 152-year time period after introduction. In accordance with the enemy release hypothesis , they found that insect damage was nonexistent during the establishment phase of this species, and in accordance with the evolution of increased competitive ability hypothesis , they found that defense compounds of plants from the introduced range were significantly lower than those of plants from the native range. Further, defense compounds increased after the accidental introduction of a specialist insect herbivore from the native range. Another approach to examine factors that contribute to invasion success is to study a group of introduced species, both invasive and noninvasive. For example, Suarez et al. examined unintentionally introduced ant species from port-of-entry samples stored at the National Museum of Natural History. They found that 12% of 232 introduced species have become established in the USA, and that the probability of establishment was influenced by propagule pressure and nesting habit of ant species. Similar investigations of intentional introductions,hydroponics growing system such as bio-control agents and horticultural plants , also may provide important information on species-level ecological traits as well as phylogenetic patterns and evolutionary processes related to invasion success.
Natural history collection data are not quantitative and include species occurrences only . In addition, especially when dealing with few samples, there is a concern about how representative the samples are of the introduced populations. In some cases, these concerns can be alleviated and relative abundances of invaders can be determined from passive sampling techniques that indiscriminately collect specimens . Also, relative abundances may be inferred using specimens as a random sample of the associated community. For example, changes in the composition of pollen loads collected from bumble bee specimens reflected changes in abundance of an invasive weed in northwestern Europe . Similarly, insect and other animal specimens could be used to examine invasive parasitoids, parasites, and pathogens, and plant specimens could be used to examine invasive herbivores and pathogens. Despite the limitations of natural history collections, numerous studies have demonstrated the utility of these collections in the study of invasion biology.Natural history collections from museums and herbaria contain a wealth of data that may be used in the study of biological invasions. For example, Suarez and Tsutsui estimated that more than 100 million insect specimens are contained in just 11 entomological collections in the United States. Worldwide, natural history collections contain billions of specimens that have been collected over hundreds of years and these collections are continuing to grow . Natural history collections provide a valuable source of preserved biological materials ranging from whole organisms to DNA libraries and cell lines. Collection specimens are associated with, at minimum, information on the date and locality of collection, and often have additional information, including associated observational data and physical samples derived from specimens, such as frozen tissues and DNA extracts. Furthermore, much of the data housed in natural history collections recently has been digitized and is available through a number of searchable databases and online resources. Biodiversity informatics is an emerging field of science, and great strides have been made to link available genetic, species, and ecosystem level data, and make these data available electronically to users worldwide . The Invaders Database System , National Biological Information Infrastructure , Global Biodiversity Information Facility are just a few examples of online data portals and resources that provide access to a global network of biodiversity information, including data on voucher specimens located in natural history collections found throughout the world .
The Invaders Database System is focused on the Pacific Northwest region of the USA and combines manually entered herbarium records dating back to 1877 with records from regional literature, extension agents, and state agriculture departments, providing presence data that allow researchers to examine historical spread.For example, GBIF provides access to 285 data providers, 7445 datasets, and nearly 175 million searchable records. Some online data sources, such as Lifemapper and the Ocean Bio-geographic Information System provide links to data from a number of collections as well as tools for mapping and predicting species distributions using linked data. Such online resources will only continue to enhance the accessibility of data; however, many natural history collections are still making efforts to digitize available data. Thus, invasive species researchers should be aware that there may be a number of local, regional, and taxon- specific collections containing voucher specimens with potentially important data that are not yet summarized electronically.Improvements to natural history collection data accessibility are well underway, as many curated collections are being digitized and made available on the internet. Digitization of collection data is important for invasive species researchers who may want to use these collections, and the linking of many collections through a data portal or centralized database increases the power of available data. To facilitate the study of early-stage invasions, we recommend that researchers and field collectors, who often are very familiar with the flora or fauna within the regions they study, collect and deposit voucher specimens in the appropriate natural history collection when new or rare species are detected, in particular those species of foreign origin. Further, if an introduced species is observed in a new habitat, it would be especially useful to collect multiple individuals and to record the number of individuals observed in the population. Also voucher specimens for biological control introductions and new horticultural introductions should be deposited in the appropriate natural history collection with pertinent data, including geographic source of origin. In particular, we recommend that natural resource managers and researchers introducing bio-control agents deposit voucher specimens with data including the number of individuals introduced, the original source population of agents, the laboratory where they were reared, and the location of introduction. Because substantial efforts are being made to digitize and link data from natural history collections through centralized data portals and databases, these vouchers may be especially useful for future investigations.
Considering the potential benefits of UA for improved ecosystem functioning, in this review we discuss the ability of UA to support local and landscape level biodiversity, the role of UA in providing ecosystem services,mobile vertical grow tables and the agenda for future UA research.Urban agriculture activities are diverse and can include the cultivation of vegetables, medicinal plants, spices, mushrooms, fruit trees, ornamental plants, and other productive plants, as well as the keeping of livestock for eggs, milk, meat, wool, and other products. This definition points to the fact that UA is not solely for food production, but for a wide range of needs of the local community, including medicinal and ornamental plants. The different types of UA allow for a diverse set of vegetation structures to contribute to the edible landscape in a range of community types, and this wide range of products means that UA systems are highly heterogeneous in size, form, and function. A description of different types of UA can be found in Table 1, with associated images in Fig. 1. Community or allotment gardens often represent small-scale, highly-patchy, and qualitatively rich semi-natural ecosystems and are usually located in urban or semi-urban areas for food production . Private gardens are primarily located in suburban areas and may be the most prevalent form of urban agriculture in cities. Privately owned gardens cover an estimated 22–27% of the total urban area in the UK , 36% of urban area in New Zealand , and 19.5% of the urban area in Dayton, Ohio, USA . Easement gardens are located within private/community properties, but are often regulated by the local government. Urban easements are established with the purpose of improving water quality and erosion control , but they can include a wide array of biodiversity, depending on management type . Roof-top gardens are any garden established on the roof of a building and can be both decorative and used for agriculture. Urban orchards are tree-based food production systems that can be owned and run privately or by the community. Increasingly, schools and hospitals are establishing fruit trees that provide crops, erosion control,shade, and wild life habitat, while producing food for the local community . Many UA systems may fit into more than one category. For example, both private gardens and community gardens may exist as rooftop gardens, and community orchards may exist within community gardens.Urban landscapes are typically highly simplified, intensively developed ecosystems with low levels of native biodiversity . However, urban green spaces such as UA can bring diverse green infrastructure back into the urban system, providing vegetative structure and biodiversity for ecosystem function and services across fragmented habitats and spatial scales . UA may be especially important for biodiversity conservation in cities because vegetative structural complexity in simplified landscapes contributes disproportionately more to conservation than in more natural landscapes . Just as in agricultural systems where more complex agri-environment management can have a larger effect on biodiversity when implemented in simple agricultural landscapes than more complex landscapes , UA provides many opportunities for re-vegetating the landscape at the local scale within a vegetatively depauperate urbanized landscape. Urban agriculture has the potential to support biodiversity not only within UA sites, but also nearby due to a landscape-mediated ‘spill over’ of energy, resources, and organisms across habitats. Such spill over may be an important process for the persistence of wildlife populations in human-dominated landscapes because it allows for resource acquisition and re-colonization events . At the same time, chemical, water, and animal movement is bi-directional, and intensified management implemented in backyards, such as pesticide application, extensive pruning, frequent mowing and other disturbances, can limit the capacity of gardens to maintain rare or sensitive insect species . Thus, it is important to understand that not all biodiversity is necessarily “good” biodiversity, and there may be a number of disservices that come from UA as well . Here, we examine the ability of UA systems to support vegetative, insect, and vertebrate biodiversity .The wide variety of UA types in practice allow for considerable variation in vegetative complexity and diversity. Domestic gardens vary widely in features that may promote plant biodiversity,such as ponds,moss, ground cover, and varied vascular vegetative structures . For example, tropical home gardens have stratified vegetation similar to those seen in multi-stratified agroforestry systems and can thus provide a large amount of planned and associated biodiversity . The diversity of vegetation types within home gardens has been documented in Santarem, Brazil, where 98 plant species were identified in 21 urban gardens and included a large diversity of fruit trees and shrubs , ornamental plants , vegetable/herb plants , and medicinal plants . In Leon, Nicaragua, 293 plant species belonging to 88 families were recorded across 96 surveyed home gardens, ranging in habit and taxonomic origin . In Hobart, Australia, 12 distinctly different garden types with different species, habits, and canopy heights were documented in front and backyard gardens , and a similar survey conducted in Toronto found 25 woody plant species and 17 different herbaceous plant species per backyard garden . In an example from five UK cities, more than 1000 species were recorded in 267 gardens, exceeding that recorded in all other local urban and semi-natural habitats .In Stockholm, allotment gardens are older than many backyard gardens, often representing lush, well-managed flower-filled areas ranging in size . Such areas are often extremely rich in plant diversity, with more than 440 different plant species recorded in a single 400 m2 allotment garden .