▪ Abstract Nonindigenous species can bring about a form of extinction of native flora and fauna by hybridization and introgression either through purposeful introduction by humans or through habitat modification, bringing previously isolated species into contact. These phenomena can be especially problematic for rare species coming into contact with more abundant ones. Increased use of molecular techniques focuses attention on the extent of this underappreciated problem that is not always apparent from morphological observations alone. Some degree of gene flow is a normal, evolutionarily constructive process, and all constellations of genes and genotypes cannot be preserved. However, hybridization with or without introgression may, nevertheless, threaten a rare species' existence.

https://www.jstor.org/stable/pdfplus/2097230.pdf

Extinction by hybridization and introgression

1. Introductory remarks 2. Convolvulacaea 2. Scrophulariaceae, Gesneriaceae, Labiatae, etc. 4. Cruciferae, Papaveraceae, Resedaceae, etc. 5. Geraniaceae, Leguminosae, Onagraceae, etc. 6. Solanaceae, Primulaceae, Polygoneae, etc. 7. Summary of the heights and weights of the crossed and self-fertilised plants 8. Difference between crossed and self-fertilised plants in constitutional vigour and in other respects 9. The effects of cross-fertilisation and self-fertilisation on the production of seeds 10. Means of fertilisation 11. The habits of insects in relation to the fertilisation of flowers 12. General results Index.

The Effects of Cross and Self Fertilisation in the Vegetable Kingdom: CONVOLVULACEÆ

We report estimates of declines of natural ecosystems in the United States, provide a rationale for ecosystem-level conservation, discuss decline and threat as criteria for conservation, and relate ecosystem losses to endangerment at species and population levels. Ecosystems are defined generally and at various spatial scales and include vegetation types, plant associations, natural communities, and habitats defined by floristics, structure, age, geography, condition, and other ecologically relevant factors. The methodology for this report consisted of a literature review and a survey of conservation agencies and professionals. The results of this preliminary study indicated significant losses of biodiversity at the ecosystem level in the United States. The most substantial losses were summarized by listing ecosystems as critically endangered (>98% decline), endangered (85-98% decline), and threatened (70-84% decline). We identified more than 30 critically endangered, 58 endangered, and more than 38 threatened ecosystems. Losses of all kinds of ecosystems have been most pronounced in the South, Northeast, and Midwest, and in California. We suggest that integrated conservation plans for all ecosystems be developed in each ecoregion of the United States, starting with types and regions that sustained the greatest losses and are at greatest risk of further loss. Conservation plans could be based on detailed studies of ecosystem status and trends and include quantitative analyses of ecosystem decline, ecological consequences of loss and degradation, and current and potential threats to each ecosystem. Ecosystem conservation need not be restricted to pristine sites, which are now almost nonexistent. Rather, management and, where possible, restoration plans for native biodiversity in partially disturbed sites should be considered.

Endangered Ecosystems of the United States: A Preliminary Assessment of Loss and Degradation

Food webs in the real world are much more complex than food-web literature would have us believe. This is illustrated by the web of the sand community in the Coachella Valley desert. The biota include 174 species of vascular plants, 138 species of vertebrates, more than 55 species of arachnids, and an unknown (but great) number of microorganisms, insects (2,000-3,000 estimated species), acari, and nematodes. Trophic relations are presented in a series of nested subwebs and delineations of the community. Complexity arises from the large number of interactive species, the frequency of omnivory, age structure, looping, the lack of compartmentalization, and the complexity of the arthropod and soil faunas. Web features found in the Coachella also characterize other communities and should produce equivalently complex webs. If anything, diversity and complexity in most nondesert habitats are greater than those in deserts. Patterns from the Coachella web are compared with theoretical predictions and "empirical ge...

Complex trophic interactions in deserts: an empirical critique of food-web theory

Patterns in life history phenomena may be demonstrated by examining wide ranges of body weight. Positive relationships exist between adult body size and the clutch size of poikilotherms, litter weight, neonate weight life span, maturation time and, for homeotherms at least, brood or gestation time. The complex of these factors reduces r
max in larger animals or, in more physiological terms, r
max is set by individual growth rate. Comparison of neonatal production with ingestion and assimilation suggests that larger mammals put proportionately less effort into reproduction. Declining parental investment and longer development times would result if neonatal weight is scaled allometrically to adult weight and neonatal growth rate to neonatal weight. Body size relations represent general ecological theries and therefore hold considerable promise in the development of predictive ecology.

Relationships between body size and some life history parameters.

Ducks, geese, and swans of the world

Grouse and quails of North America

Handbook of waterfowl behavior

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Cranes of the world

Comparative biology: Taxonomy, phylogeny, and zoogeography Reproductive biology Ecology and population dynamics Ontogeny of plumages and behaviour Adult vocalizations and non-vocal behaviour Species accounts: Subfamily Odontophorinae Dendrortyx Philortyx Oreortyx Callipepla Colinus Odontophorus Dactylortyx Cyrtonyx Rhynchortyx Tribe Perdicini Lerwa Tetraophasis Tetraogallus Alectoris Ammoperdix Francolinus Perdix Rhizothera Margaroperdix Melanoperdix Coturnix Anurophasis Perdicula Ophrysia Arborophila Caloperdix Haematortyx Rollulus Ptilopachus Bambusicola Galloperdix Bibliography Index.

Paul A. Johnsgard

Papers

Ducks, geese, and swans of the world

Grouse and quails of North America

Handbook of waterfowl behavior

Cranes of the world

The quails, partridges, and francolins of the world