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Germination of Exhumed Weed Seed in Nebraska
- Orvin C. Burnside, Charles R. Fenster, Larry L. Evetts, Robert F. Mumm
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- Journal:
- Weed Science / Volume 29 / Issue 5 / September 1981
- Published online by Cambridge University Press:
- 12 June 2017, pp. 577-586
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- Article
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An experiment was initiated in 1970 and continued through 1979 by exhuming and germinating seed of 12 economic weed species buried beneath 23 cm of soil in eastern and western Nebraska. Loss in germination of exhumed seeds over years is mathematically characterized by the formula for the rectangular hyperbola, which represents many shapes of curves that have zero as their lower limit. Of the 12 weed species, only fall panicum (Panicum dichotomiflorum Michx.) and redroot pigweed (Amaranthus retroflexus L.) seed germination did not drop significantly over the 10-yr burial period. Germination of redroot pigweed seed was higher when buried in eastern Nebraska, but was higher for smooth groundcherry (Physalis subglabrata Mack&Bush.) and velvetleaf (Abutilon theophrasti Medic.) when buried in western Nebraska. Germination of the other nine species were not affected by burial location. The 12 weed species can be ranked as those showing most to least rapid loss of germination during burial for 10 yr as follows: honeyvine milkweed [Ampelamus albidus (Nutt.) Britt.], hemp dogbane (Apocynum cannabinum L.), kochia [Kochia scoparia (L.) Schrad.], sunflower (Helianthus annum L.), large crabgrass [Digitaria sanguinalis (L.) Scop.], common milkweed (Asclepias syriaca L.), musk thistle (Carduus nutans L.), velvetleaf, fall panicum, redroot pigweed, green foxtail [Setaria viridis (L.) Beauv.], and smooth groundcherry.
3 - Inbreeding and outbreeding depression in fragmented populations
- Edited by Andrew G. Young, Division of Plant Industry CSIRO, Canberra, Geoffrey M. Clarke, Division of Entomology, CSIRO, Canberra
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- Book:
- Genetics, Demography and Viability of Fragmented Populations
- Published online:
- 29 January 2010
- Print publication:
- 12 October 2000, pp 35-54
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Summary
ABSTRACT
The goal of this chapter is to review inbreeding and outbreeding depression in the context of habitat fragmentation and to show how smaller, fewer populations of any organism separated by distance may exasperate the effects of these two genetic phenomena. We review the genetic basis of each, provide examples, and discuss specific empirical issues that need to be addressed in future research. We conclude with an illustrative case study of how both genetic phenomena can act simultaneously in a single species.
INTRODUCTION
Most rare and endangered species exist as small, isolated populations (Holsinger & Gottlieb, 1989). Unfortunately this seems to be the fate of even common species as natural populations are becoming increasingly fragmented. Fragmentation reduces the number of breeding individuals within a population while reducing gene flow between populations. Consequently, mating between individuals in fragmented populations is more likely to represent selfing (if genetically feasible) and/or biparental inbreeding (matings between related individuals) resulting in inbred offspring. The deleterious consequences of inbreeding are manifold. Inbred progeny may suffer from inbreeding depression, i.e. a decline in fitness, where the relative performance of the resulting inbred progeny is lower compared to progeny produced from matings between unrelated individuals within a population (Falconer & Mackay, 1996). Continued inbreeding associated with small populations also results in the loss of within-population genetic diversity (e.g. Schoen & Brown, 1991). Genetic diversity may influence the colonising ability and persistence of a population (Barrett & Kohn, 1991; Lande, 1994). Decreased genetic diversity may also be associated with increased susceptibility to pathogens and pests (Frankham, 19951b).
2 - Genetic considerations for plant population restoration and conservation
- Edited by Marlin L. Bowles, Christopher J. Whelan
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- Book:
- Restoration of Endangered Species
- Published online:
- 27 January 2010
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- 27 October 1994, pp 34-62
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Summary
Introduction
Successful restoration policy involves three basic criteria. First, sufficient habitat must be protected for the continued persistence of a species (Gilpin & Soulé 1986). Second, demographic information must be collected to determine which life history stages are most critical to survival, reproduction, and longterm population vigor (Marcot & Holthausen 1987, Lande 1988). Third, once these fundamental criteria for population survival are met, genetic variation can be considered as an issue in restoration and conservation policy. Overall, we believe that genetic issues may be more pertinent to population restoration than to population conservation. In attempting to conserve taxa, one is initially interested in saving numbers of individuals regardless of their relatedness. Given that natural areas managers will have the opportunity to reintroduce populations that have been extirpated in nature, it seems reasonable that any genetic manipulations that may help restore a population's vigor in situ for the short or long term may be beneficial.
Rare and endangered taxa often exist as a few relatively small populations (Holsinger & Gottlieb 1989) subject to population bottlenecks. Thus, genetic drift and mating among relatives contributes to the loss of genetic variation and reduction in the population's overall vigor through inbreeding depression (Lacy 1987, Polans & Allard 1989). A short-term conservation goal should be to ensure that the vigor of a population is maintained or restored in the face of inbreeding by appropriate manipulation of the remaining genetic variation (Ledig 1986).