Search Results

This chapter describes the physical, chemical, and biotic features of the main types of ice-based aquatic ecosystems. Dark-coloured sediments on and in ice enhance absorption of solar radiation, promote melting, and the formation of habitats of varying sizes and longevity. These range from ‘bubbles’ within glacial and perennial lake ice (~10^-2 m diameter), cryoconite holes (~10^-1 -10⁰ m diameter) on ice surfaces to large melt lakes (~10¹ - 10² m diameter) and rivers on ice shelves and ice sheets. For the most part, the development of ice-based aquatic ecosystems depends on liquid water. Communities are predominantly microbial, with cyanobacteria and algae dominating the phototrophs, while microinvertebrates with stress-tolerate strategies (rotifers, tardigrades, and nematodes) are also present. The chapter argues that ice-based ecosystems represent important biodiversity elements within polar landscapes, and would have been essential refugia from which polar region ecosystems recovered after periods of extended glaciation.

Although Bt transgenic plants are ecologically benign compared with insecticide sprays, there is a concern that insects will eventually evolve resistance to Bt toxin. If that happened, then the transgenic plants would no longer control the pest insects. The mechanism of how Bt toxins kill target insects, and the strategies that have been proposed to delay the onset of resistance to Bt are described. The two most important management practices are high doses of toxin and refugia. For the high dose strategy, a lot of Bt protein is produced in the plant, which makes a high hurdle for evolution to jump in a single bound. The refugia strategy requires non-transgenic plants to be planted in fields next to transgenic crop fields. This would allow large numbers of potential mates for which there is no pressure to evolve resistance that could interbreed with the very rare resistant insects. In combination, these strategies have proven effective.

The Late Quaternary palaeoecological record represents a source of baseline data for evidence-based conservation, by providing novel insights into how organisms and environments are likely to respond to the negative effects of future climate change. Palaeoecological data can reveal how individual taxa have responded in the past to specific climatic and environmental changes, and can suggest the kinds of processes that are likely to take place in the future at a broader ecological level. Conservation priority should be given to populations living in ‘long-term’ or ‘true’ geographic refugia where genetic diversity evolves. A lack of consideration of intraspecific-level extinction, increasingly recognised in the Quaternary record, has hampered interpretation of the causes of past species extinctions. Non-analogue ecological communities are commonly observed in the Quaternary record, suggesting that there will be a significant level of unpredictability in environmental responses to climatic change at the community level.

This chapter examines the zoogeographic affinities of 75 Plecoptera species in New Mexico and Arizona. The findings indicate that in four major physiographic subdivisions of the study area, stonefly species arrange themselves in ways that reveal dispersal corridors, dispersal barriers, and refugia which operated during late Pleistocene pluvial and post-pluvial Holocene environments. The results also suggest that the southwestern Plecoptera fauna are distinct in their species composition, taxonomic representation, and level of endemism.

Consistent Phylogeographic Patterns across Taxa and Major Evolutionary Events Mediterranean to alpine climates (combined with vicariant events associated with glaciations, changing sea levels, and rapid mountain formation) have resulted in the formation of deep and shallow divergences. Significant events include the formation of the Klamath-Siskiyou ranges, the Coastal Range, and the Transverse and Peninsular Ranges; growth of and glaciation events in the Sierra Nevada; Bering Land Bridge; stabilization of the Mediterranean climate; connection between North and South America; connection between the Pacific Ocean and the Central Valley in the Monterey area; flooding of the Los Angeles Basin and the Salton Trough, formation of the Channel Islands and their connections to land, and the Bouse Embayment. Refugia and high levels of diversity for multiple taxa are identified in multiple regions that reflect both diversification and hybridization through secondary contact. Questions remain about the extent of differentiation of species in alpine environments; further exploration is warranted in areas identified with high levels of neoendemism. Regional analyses of species origins would provide insight into the development of the California biota, particularly in areas that are known suture zones. The concordance of phylogeographic breaks across divergent taxa supports the commonality of processes that shape the speciation of the biota of California. It is important to consider the influences of life-history characteristics and ecological requirements that affect lineages differently in time and space.

As mediterranean-type climate (MTC) regions emerged and expanded, species from the regional pool colonized and persisted in these new climate regions. In general, taxa were derived from a few types of historical ‘geoflora’ communities: temperate forest, subtropical and tropical, and semi-arid or arid. Some of the taxa within modern mediterranean-type vegetation represent relatively ancient relict taxa that pre-date the emergence of mediterranean-type drivers. Other lineages underwent subsequent speciation, resulting in the evolution of new MTC region-specific taxa, including the production of many new species through evolutionary radiations. Low extinction rates associated with historically stable climate and limited recent geological activity might explain the high diversity found in some MTC regions, while in regions with more topographical variation the ability of species to move across elevation gradients has been suggested also to have allowed species to be buffered from climatic changes that may otherwise have led to extinctions.

The waved albatross of Galápagos, the world’s only tropical albatross, has survived millennia of flying in low-velocity winds by foraging relatively short distances to the Peruvian upwelling. The advent of longline fishing along the coast of Peru and recent changes in El Niño have caught the albatross in a demographic pinch, rendering it critically endangered since 2007. Because reproductive pairs lay only a single egg per year under the best of circumstances, the conservation challenges are noteworthy and all the more serious because recurrent El Niño events shut down the albatrosses’ food supply. Effective conservation measures include human intervention to save “marooned” and abandoned eggs, to change longlining practices in the Peruvian coastal fishery, and to provide safe refugia on a small island off the coast of Ecuador where hungry albatrosses can raise chicks even closer to the upwelling. But until our efforts suffice to reduce greenhouse gas emissions and the growing severity of El Niño events, we shall all have an albatross hanging around our necks: the beautiful waved albatross of Galápagos.

Warning colour patterns in Heliconius show great diversity as well as convergence due to mimicry. This chapter considers the origins of such diversity. Heliconius have been proposed as an example of the ‘shifting balance’, an evolutionary model involving a balance between drift and selection. Although alternative mimicry patterns can move around the species range (Phase III), there is only weak evidence for genetic drift causing evolutionary novelty in wing patterns (Phase I). There is also weak evidence for the origin of novel patterns in Pleistocene forest refugia. Sequencing of the genes that control wing pattern diversity has revealed a surprising and complex history. Within-species disjunct populations with similar wing patterns show a common origin, suggesting a complex history of movement of patterning alleles across species ranges. Between species, convergent mimetic forms share alleles, likely due to adaptive introgression. Closely related species therefore evolve mimicry by sharing of alleles rather than independent convergence. These patterns contrast with phylogeographic and phylogenetic relationships inferred from the rest of the genome, and suggest caution in inferring the history of adaptive traits from ‘neutral’ molecular markers.

This chapter considers the challenges faced by plant conservation in the Middle East, outlining what is needed for successful conservation. It describes how humans are exacerbating the ongoing effects of desertification, including wood collection, road construction, and extractive petroleum-related technologies. Meanwhile, massive coastal developments are degrading the diverse and productive marine ecosystems. Agriculture continues to stress the regional ecology through overstocking of livestock, land conversion, and ephemeral agriculture. Negative consequences of wadi-damming and water recharge wells all create additional challenges and the hydro-politics are a major source of conflict. The region’s major biodiversity hotspots are described, including the Horn of Africa and Eastern Afromontane regions, Eastern Mediterranean basin, the Irano–Anatolian region with its ancient “Hyrcanian” forestland south of the Caspian, and the Caucasus mountain refugia of Arcto–Tertiary relicts (with the Colchic and Hyrcan forests there and in Hyrcanian Iran being among the oldest forests in western Eurasia).

Present day genetic diversity within the Greater Cape Floristic Region (GCFR) is attributed to diversification during the Pliocene (5–2.5 Ma) and Pleistocene (2.5 Ma–20,000), due to the substantial phylogeographic structuring in many taxa examined, including plants, invertebrates, amphibians, reptiles, mammals, and birds. Diversification on this timescale is relatively recent, and the result is characteristically shallow genetic lineages, recently radiated species, and species complexes. Most phylogeographic structure is attributed to diversification events in the Late Miocene and Pliocene, often associated with recently diverged species which are usually reciprocally monophyletic but exhibit shallow divergences. More recent diversification events date to the Pleistocene, but these appear to be either divergence events among populations within species, or in some cases between species that are not reciprocally monophyletic and share ancestral polymorphisms. Discrete geographic boundaries among these clades are sometimes blurred, with alleles or haplotypes shared across some geographic regions or habitat types. Across the entire region, genetic diversity appears to be higher in the western GCFR, as compared to the east. This is possibly explained by the high stability of the region, and the associated potential for multiple refugia in the west. Regardless, the finer-scale patterns are not congruent among major groups, i.e. plants, invertebrates, amphibians, reptiles, mammals and birds, or within them, suggesting that there is no set of common environmental factors that can explain the phylogeographic patterns and cladogenesis in the GCFR. Instead, species presumably respond differentially depending on their habitat requirements, life history, and adaptive potential.

Ectothermic organisms experience their local environments in ways that humans can have difficulty conceptualizing. Physics-based (ecomechanical) approaches, for example heat budget models, can lend insights into how an organism’s very local environmental conditions (microclimate) can drive niche-level conditions such as body temperature; these in turn drive physiological processes. Quantitative methods also allow insights into the temporal and spatial scales that may ultimately determine responses to larger-scale environmental change. For example, for small, sessile organisms, microhabitats such as crevices in rocks may provide microrefugia that allow survival during heat waves. As a result, larger-scale recovery following heat waves (rescue effects) may ultimately be influenced by much smaller-scale processes. Ecomechanics techniques also facilitate the use of interventions such as shading that can maintain environmental conditions within physiological tolerance levels.

It is increasingly recognized that, as a result of ever-growing atmospheric inputs of greenhouse gases like carbon dioxide from the burning of fossil fuels, the climate is changing regionally and globally. This has been affirmed, in light of increasing scientific understanding, in the latest report of the Intergovernmental Panel on Climate Change (IPCC) in 2001, by the US National Academy of Sciences in its 2001 report, and most recently by a statement from the Science Academies of all G8 countries, along with China, India, and Brazil. This latter statement calls on the G8 nations to ‘Identify cost-effective steps that can be taken now to contribute to substantial and longterm reduction in net global greenhouse gas emission [and to] recognize that delayed action will increase the risk of adverse environmental effects and will likely incur a greater cost’. Global warming caused by elevated greenhouse gas levels is expressed with long time lags, which can be difficult to appreciate by those unfamiliar with physical systems. Once in the atmosphere, the characteristic residence time of a carbon dioxide molecule is a century. And the time taken for the ocean’s expansion to come to equilibrium with a given level of greenhouse warming is several centuries. If current trends continue, by around 2050 atmospheric carbon dioxide levels will have reached more than 500 parts per million, which is nearly double pre-industrial levels. The last time our planet experienced levels this high was some 20–40 million years ago, when sea levels were around 100m higher than today. It can also be difficult to relate intuitively to the seriousness of the roughly 0.7 °C average warming of the Earth’s surface over the past century. And the warning by the IPCC in its 2001 report, that global warming would be in the range of 1.4–5.8 °C by the end of this century, may also seem unalarming when we experience such temperature swings from one day to the next. There is, however, a huge difference between daily fluctuations, and global averages sustained year on year; the difference in average global temperature between today and the last ice age is only around 5 °C.

This chapter first details the advent of post-glacial period at northern latitudes after ice volumes peaked about 21,000 years ago. There were a number of climatic oscillations during the final stages of the glacial period referred to as the Bølling-Allerød interstadial (14,700–12,900 BP), which began with the Oldest Dryas and ended abruptly with the onset of the Younger Dryas. The start of the Holocene is generally considered to be the termination of the Younger Dryas period, which in northern-western Europe was around 11,200–11,600 BP. The chapter then discusses evidence that glacial refugia contributed to the genetic inheritance of the modern arctic flora; the reconstruction of past plant distributions; the Pleistocene megafauna decline and survival; the Hypsithermal, or Xerothermic, or Climatic Optimum; and late Holocene climate fluctuations.