... cylindropuntias (chollas) was measured at a series of sites from west to east across the Moja... more ... cylindropuntias (chollas) was measured at a series of sites from west to east across the Mojave Desert of southern California, and here results from Acton (34°28 ' N, 118 ° 14' W; one species), Yucca Valley (34°06 ' N, 116°27'W; two species), Joshua Tree National Monument ...
LETTERS TO THE EDITORS 371 THE CONSISTENCY OF INTRA-AND INTER-CONTINENTAL GRASSLAND BIRD SPECIES ... more LETTERS TO THE EDITORS 371 THE CONSISTENCY OF INTRA-AND INTER-CONTINENTAL GRASSLAND BIRD SPECIES COUNTS INTRODUCTION Evolutionary biologists (Hutchinson, 1957; MacArthur, 1965, and earlier; Patrick, 196З) have often discussed the ...
. To investigate survivorship and regeneration in desert perennial plants, individual shrubs were... more . To investigate survivorship and regeneration in desert perennial plants, individual shrubs were mapped, measured and tagged on a nearly level 360 m2 plot of diverse Mojave Desert vegetation in 1981, they were re‐mapped and measured 15 years later, in 1996. A large majority of the shrubs persisted between censuses. Modest birth (establishment) and death rates indicate that plants are replaced approximately every century, while the median longevity of several species is much longer. A 15‐yr intercensus interval, appropriate for most species (i.e. birth and death rates were measurable), is too short for several larger shrubs (including Larrea divaricata, Ephedra nevadensis, Yucca schidigera and the larger Opuntia spp.) in which virtually no births or deaths occurred and in which longevity must be extremely high.While individuals of most species grew over the 15‐yr interval, others did not, and some individuals shrank in size. In a number of species, individual growth rates were significantly reduced according to the number of neighbouring plants rooted 0.5–2.0 m distant. Even Larrea tridentata, one of the largest species, showed significant effects of growth rate reduction where crowded by allospecific plants, despite the generally much smaller sizes of these neighbours.
ABSTRACT Morphological variability is extremely high in the Australian mulga, Acacia aneura, even... more ABSTRACT Morphological variability is extremely high in the Australian mulga, Acacia aneura, even within local populations. This variation appears to be genetically based, and its maintenance can be related to two sorts of hypotheses: (a) ecotypic selection for morphological divergence related to the segregation of individuals into distinct, autogenic microniches, and (b) apostatic selection to foil foliar herbivores or seed predators. Morphological variation in the growth form, phyllodes, and pods of mulga is analyzed within and among populations at five topographically uniform sites in southwestern Australia along a gradient of annual precipitation. Phenotypic variability among sites is negatively correlated with annual precipitation, while within sites growth form and phyllode variability covary, and phyllode morphology covaries with pod morphology. Although the two sorts of hypotheses, ecotypic versus apostatic selection, are not clearly separable by morphological data alone, the former appears to be ...
... populations MARTIN L. CODY and JACOB McC. ... Especially notable are the Hawaiian silversword... more ... populations MARTIN L. CODY and JACOB McC. ... Especially notable are the Hawaiian silverswords and greenswords (Argyroxiphium, Dubautia, Wilksia), which are derived from Californian tarweeds (Rail-lardella or Raillardiopsis; Carlquist 1966b; Baldwin et al. ...
... cylindropuntias (chollas) was measured at a series of sites from west to east across the Moja... more ... cylindropuntias (chollas) was measured at a series of sites from west to east across the Mojave Desert of southern California, and here results from Acton (34°28 ' N, 118 ° 14' W; one species), Yucca Valley (34°06 ' N, 116°27'W; two species), Joshua Tree National Monument ...
LETTERS TO THE EDITORS 371 THE CONSISTENCY OF INTRA-AND INTER-CONTINENTAL GRASSLAND BIRD SPECIES ... more LETTERS TO THE EDITORS 371 THE CONSISTENCY OF INTRA-AND INTER-CONTINENTAL GRASSLAND BIRD SPECIES COUNTS INTRODUCTION Evolutionary biologists (Hutchinson, 1957; MacArthur, 1965, and earlier; Patrick, 196З) have often discussed the ...
. To investigate survivorship and regeneration in desert perennial plants, individual shrubs were... more . To investigate survivorship and regeneration in desert perennial plants, individual shrubs were mapped, measured and tagged on a nearly level 360 m2 plot of diverse Mojave Desert vegetation in 1981, they were re‐mapped and measured 15 years later, in 1996. A large majority of the shrubs persisted between censuses. Modest birth (establishment) and death rates indicate that plants are replaced approximately every century, while the median longevity of several species is much longer. A 15‐yr intercensus interval, appropriate for most species (i.e. birth and death rates were measurable), is too short for several larger shrubs (including Larrea divaricata, Ephedra nevadensis, Yucca schidigera and the larger Opuntia spp.) in which virtually no births or deaths occurred and in which longevity must be extremely high.While individuals of most species grew over the 15‐yr interval, others did not, and some individuals shrank in size. In a number of species, individual growth rates were significantly reduced according to the number of neighbouring plants rooted 0.5–2.0 m distant. Even Larrea tridentata, one of the largest species, showed significant effects of growth rate reduction where crowded by allospecific plants, despite the generally much smaller sizes of these neighbours.
ABSTRACT Morphological variability is extremely high in the Australian mulga, Acacia aneura, even... more ABSTRACT Morphological variability is extremely high in the Australian mulga, Acacia aneura, even within local populations. This variation appears to be genetically based, and its maintenance can be related to two sorts of hypotheses: (a) ecotypic selection for morphological divergence related to the segregation of individuals into distinct, autogenic microniches, and (b) apostatic selection to foil foliar herbivores or seed predators. Morphological variation in the growth form, phyllodes, and pods of mulga is analyzed within and among populations at five topographically uniform sites in southwestern Australia along a gradient of annual precipitation. Phenotypic variability among sites is negatively correlated with annual precipitation, while within sites growth form and phyllode variability covary, and phyllode morphology covaries with pod morphology. Although the two sorts of hypotheses, ecotypic versus apostatic selection, are not clearly separable by morphological data alone, the former appears to be ...
... populations MARTIN L. CODY and JACOB McC. ... Especially notable are the Hawaiian silversword... more ... populations MARTIN L. CODY and JACOB McC. ... Especially notable are the Hawaiian silverswords and greenswords (Argyroxiphium, Dubautia, Wilksia), which are derived from Californian tarweeds (Rail-lardella or Raillardiopsis; Carlquist 1966b; Baldwin et al. ...
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