Similarly, a comparison of herbivory damage on herbarium specimens of non-native plants in urban versus rural environments might provide insights into one pathway towards species invasion. Many non-native plant species are introduced into urban areas, and urbanization may provide warm, enemy-free space where they can establish and subsequently expand. Though the role of urbanization in natural enemy release and subsequent invasions is not well characterized, we might predict that non-native plants escape their natural enemies in urban areas and experience increased herbivory rates when they move into natural areas where they encounter a higher diversity of herbivores.Responses to global change, such as those in space and time, discussed above, encompass plasticity in behaviour or physiology and distributional shifts, which may be rapid. However, there is growing evidence that evolutionary responses might also be rapid, assuming there is sufficient standing genetic variation for selection to act upon. While fluctuating selection can maintain this standing variation, providing the raw material for future adaptive responses, strong directional selection, such as that imposed by anthropogenic climate warming, plastic gardening pots can erode genetic variation and potentially impede evolutionary adaptation, elevating population extinction risk.
Insect herbivores and the plants they feed upon are locked in an evolutionary arms race, and insect herbivory drives contemporary plant evolution, changing plant allele frequencies within a few generations. It is likely that climate-induced shifts in herbivory will impose additional selection on both plants and insect herbivores already under pressure from direct effects of climate change. Natural history collections that span multiple generations can provide a record of evolutionary changes and constraints. It can be difficult, however, to disentangle plastic and evolutionary responses. Evolutionary responses can be predicted from the breeder’s equation, but this requires extensive long-term population data. For species that can be stored in a dormant state, such as plants, it is possible to contrast ancestral and descendent genotypes grown under common conditions, and Franks et al. were able to demonstrate evolution to earlier flowering in Brassica using stored seeds. Seedbanks and other collections that hold propagules, intentionally or incidentally, could thus provide important data for exploring evolutionary responses and testing whether species might be approaching limits in their adaptive responses. Sequencing of archived tissue of plants and animals already allows for the signature of selection to be sought directly in their DNA. New collections could systematically sample seeds through time or across populations, providing the potential to resurrect past populations and examine micro-evolutionary change.
Evolutionary insights from herbarium specimens might be particularly useful for adapting agricultural practices with global change. Alongside the insights that collections data can provide on ecological and impacts of global change in natural systems, herbaria are additionally repositories of crop wild relatives . CWR are important sources of phenotypic and genetic information on pest and disease resistance that may be introgressed into crops. For example, comparative analyses of CWR might provide an opportunity to identify herbivore-resistance traits relevant to agricultural and ornamental species, such as glandular trichomes that act as physical defences against insects and can be detected on herbarium specimens with a microscope. Herbaria provide a record of this genetic diversity even when it is no longer present in the wild. In addition, herbivore damage on CWR herbarium specimens might help predict increases in pest pressure on crops, because closely related host species tend to be vulnerable to similar suites of pests and pathogens. Specimens in herbaria can also serve as records of past biotic threats and inform how we can avoid these threats in the future. For example, Yoshida et al. sequenced the genomes of Phytophthora infestans, the cause of potato late blight, infamous for its role in the Irish Potato Famine, from herbarium collections of infected potatoes and tomatoes.
Using genomic tools, they found one strain of P. infestans linked to the potato blight in the nineteenth century, but that multiple strains moved globally in the twentieth century. In a recent study, we quantified historical insect damage on a crop species, the low bush blueberry, Vaccinium angustifolium, growing in the wild to determine how pest pressure has changed with recent climate change. The low bush blueberry is an ecologically and economically important endemic species in northeastern North America, whose production has seen recent increases owing to awareness of the health benefits of blueberries. Collection records from the Harvard University Herbaria suggest that herbivore damage has increased in recent years, with evidence that increased herbivory is a result of winter climate warming. This highlights the need for increased monitoring of herbivore species on V. angustifolium and allows the development of proactive pest management practices that could be implemented before economic impacts are felt.Given the millions of plants and insect specimens that are becoming available online, it will increasingly be possible to assess changes in phenological synchrony, distributions, and occurrence over time across diverse taxa and large spatial areas. The sampling of species within museums and herbaria, however, is non-random and often sparse, which can present distinct challenges depending on the response variable of interest and how robust the data are for answering particular questions. However, the depth of sampling within natural history collections is difficult to assess because natural history collections data are often dark—without searchable databases—despite efforts to rapidly digitize. Another obstacle is that data associated with museum specimens can have large uncertainty; for example, specimens collected before the advent of geographical information system technology often have only coarse scale location data that may prohibit local-scale analyses. When assessing phenological change, the most important challenges arise because of biases in collecting. Herbarium specimens are more likely to be collected near roads; rare species are, perhaps unsurprisingly, collected less frequently, and collections are more likely to be made in spring or summer months. Such biases can make specimen data difficult to work with. For example, roads might be warmer than the surrounding countryside, and observations of shifts in phenology through time might, in part, also reflect the increasing extent of the road network. Finally, sampling frequency may bias estimates of first events, because we are more likely to observe earlier events with greater sampling intensity. Such sampling biases can make it difficult to compare across species when sampling effort varies, for example, between common and rare species. New methods offer a solution to such challenges. For example, methods have been established for calibrating species distribution models according to known biases in presence-only data, and newly constructed statistical models allow robust estimates of the tail of a distribution—in the context of phenology, first flower, for example—even when sampling is uneven. Shifting collection practices may also introduce biases. Herbivory measurements derived from herbarium specimens are probably underestimates in most cases because collectors try to avoid collecting damaged specimens. Even so, herbivory is prevalent on specimens and matches patterns derived from theory and observations from living plants. Importantly, biases introduced by collectors are not necessarily problematic if they do not vary across axes of interest. For example, if collectors are equally likely to collect relatively undamaged specimens across latitude, blueberry pot size herbarium specimens might still provide insights into how herbivory varies with latitude. When there are concerns that collecting practices may have influenced observations—for example, perhaps collectors are more or less likely to collect damaged specimens over time—collector identity may be added to statistical models to partially control for such biases. A unique challenge to using herbarium specimens is that they are eaten by a suite of insects within museums. This loss of material can reduce the use of insect specimens for morphological and genetic analyses. For plants, chewing herbivory created indoors, after a plant was collected, can be confused with damage created while plants were alive. We developed protocols that allowed us to reliably discriminate chewing damage created pre- and post- collection described in.
Such approaches, however, require careful examination of specimens with a microscope and entomological knowledge to recognize diagnostic features of damage to plants, which is a barrier to large scale, rapid scoring of chewing damage on digitized specimens. Other types of insect damage, such as leaf mines, skeletonization and galls, are almost never a product of insects eating plants within museums, and might be scored more reliably, although their prevalence is lower.We have previously argued that herbaria should be repositioned as hubs for ecological research, and we provided suggestions for how to manage collections to promote ecological research on global change. Because the vast majority of research in collections has historically been on taxonomy and systematics, collections are rarely faced with providing data for ecologists and evolutionary biologists. Stronger relationships between researchers in the field, collections managers, and digital data providers would help ecologists to better address the challenging ecological questions of global change, and, importantly, could also increase funding opportunities for maintaining and building natural history collections, which are often under-funded and threatened by institutional priorities. Here, we provide three suggestions for how natural history collections and ecologists can work together to support global change research on species interactions. First, it would be helpful to detail the sampling protocol used to collect specimens. In many cases, collecting practices are haphazard, but if, for example, a curator collects a specimen expressly to document a gall, this would change the inferences we can make from this specimen . Second, ecologists could engage with curators in projects that involve resampling areas and taxa that have long historical records, ideally at the same time of year and with the same research effort involved in previous collections. Third, specimens are most useful when researchers can associate collections with important predictor variables representing species traits or abiotic data related to global change. New opportunities exist to link specimens to the published literature and trait databases , BIEN as well as non-traditional data sources, such as written records and historical photographs. The better integration of new bio-informatics tools and digital databases within biological collections will help transition museums and herbaria into ecological data centres.The volume before you is the first systematic, comparative attempt to use the concepts and models of behavioral ecology to address the evolutionary transition from societies relying predominantly on hunting and gathering to those dependent on food production through plant cultivation, animal husbandry, and the use of domesticated species embedded in systems of agriculture. Human behavioral ecology is not new to prehistoric analysis; there is a two-decade tradition of applying models and concepts from HBE to research on prehistoric hunter-gatherer societies . Behavioral ecology models also have been applied in the study of adaptation among agricultural and pastoral populations. We review below a small literature on the use of these models to think generally about the transition from foraging to farming, while the papers collected here expand on these efforts by taking up the theory in the context of ethnographic or archaeological case studies from eleven sites around the globe.There are older transformations of comparable magnitude in hominid history; bipedalism, encephalization, early stone tool manufacture, and the origins of language come to mind . The evolution of food production is on a par with these, and somewhat more accessible because it occurred in near prehistory, the last eight thousand to thirteen thousand years; agriculture also is inescapable for its immense impact on the human and non-human worlds . Most problems of population and environmental degradation are rooted in agricultural origins. The future of humankind depends on making the agricultural “revolution” sustainable by preserving cultigen diversity and mitigating the environmental impacts of farming. Simple population densities tell much of the story. Huntergatherers live at roughly 0.1/km2 ; rice agriculturists in Java at 1,000/km2 , a ten-thousand-fold difference. There were an estimated ten million humans in the world on the eve of food production ; now oversix billion people live on this planet, an increase of 600% in only ten millennia. Agriculture is the precursor, arguably the necessary precursor, for the development of widespread social stratification, state-level societies, market economies, and industrial production . Social theory maintains that present-day notions of property, equality and inequality, human relationships to nature, etc., are shaped, at least in part, by the social organization, technology, or food surpluses entailed in our dependence on agriculture.