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  • 1
    Electronic Resource
    Electronic Resource
    Oxford, UK; Malden, USA : Blackwell Science Inc
    Restoration ecology 12 (2004), S. 0 
    ISSN: 1526-100X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Planting native species into restoration settings where other natives already occur is a common practice. However, the competitive consequences of such plantings are rarely studied. Planting density also affects restoration costs. Here we examined the effects of established individuals of Lemmon's needlegrass (Achnatherum lemmonii) on plugs of bluebunch wheatgrass (Pseudoroegneria spicata) and Idaho fescue (Festuca idahoensis) in a restoration site in Oregon. All three of these grasses are local native perennials. Plugs were planted at 6, 12, and 18 cm from established A. lemmonii bunchgrasses and also in plots without A. lemmonii neighbors. Plug survival was uniformly high, averaging more than 98%. Plugs planted at 6 cm from established grasses showed significantly lower growth and reproduction than plugs planted at 18 cm, which had similar values to plugs not planted in the vicinity of A. lemmonii. These results suggest that interplanting distances of as little as 18 cm were sufficient to greatly reduce competitive effects on newly planted plugs, at least in early establishment at this site.
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Oecologia 55 (1982), S. 243-247 
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary A three year study of Senecio keniodendron (Compositae), a giant rosette species of the alpine zone of Mt. Kenya, demonstrated that individuals which reproduce are more likely to die, and less likely to reproduce in the future if they do survive, than are vegetative individuals of the same size. However, if an individual reproduces, survives and reproduces again, then it produces more seeds during the second reproductive episode than does a plant of the same height reproducing for the first time, because reproduction is followed by production of lateral rosettes, increasing the number of potentially-reproductive rosettes per plant. Slow-growing rosettes are less likely to reproduce than fast-growing rosettes. For rosettes which do reproduce, rosette size and rate of leaf production, measured before reproduction begins, are good predictors of fecundity.
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  • 3
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 352 (1991), S. 10-10 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] SIR — Once again, the spectre of genetic depauperization has reared its head, this time overriding the possibility that introduced disease may threaten the last wild population of golden lion tamarins1. The News item in Nature reported that "plague is a risk we [the US National Zoo] feel we ...
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  • 4
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Obligate symbioses between specialized arboreal ants and plants have evolved independently in many lineages. Ant-plants (myrmecophytes) typically provide hollow nest cavities and nutrition to the occupying ant colony. In turn, resident plant-ants often protect their hosts from herbivory ...
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Oecologia 115 (1998), S. 508-513 
    ISSN: 1432-1939
    Keywords: Key words Kenya ; Spinescence ; Induced resistance ; Herbivore exclusion ; Acacia drepanolobium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Descriptive and experimental evidence suggests that spine length is an inducible defense, with longer spines being produced by branches experiencing greater levels of herbivory. Here we present results from a replicated, controlled herbivore exclusion experiment in which cattle, wildlife (large mammalian herbivores), and megaherbivores (elephants and giraffes) were independently manipulated. Experimental wildlife barriers virtually eliminated herbivory on Acacia drepanolobium branches at all heights. Megaherbivore barriers reduced herbivory on branches more than 1.75 m from the ground by up to 80%, and reduced herbivory on lower branches by 40%. These patterns of herbivory were matched by patterns of relaxation of spine length that occurred in response to the treatments. After 22 months of herbivore exclusion, the lengths of newly produced spines were 19% shorter on branches protected from large mammal herbivory than on trees in control plots. On low branches, there was a steady increase in spine length from total exclusion plots (shortest spines) to plots with wildlife to plots with both megaherbivores and wildlife (longest spines). On higher branches, new spines were shorter in total exclusion plots and wildlife plots than in plots in which megaherbivores were allowed. This is the first replicated, controlled experimental demonstration that browsing by free-ranging herbivores is associated with greater spine lengths. Examination of trees incidentally protected from herbivory for several years suggests that reduction in spine length in the experimental plots will eventually exceed 70%. Initially slow relaxation of spine length may represent a cautious adaptive strategy in an environment where a given branch is likely to escape herbivory in a given growth season, even when herbivores are present.
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Oecologia 86 (1991), S. 70-75 
    ISSN: 1432-1939
    Keywords: Induced defense ; Spinescence ; Thorns ; Giraffe ; Herbivory
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary We report evidence from controlled experiments that long straight thorns deter herbivory by browsers. Cut branches of three woody species that had their thorns removed suffered significantly greater herbivory by a tethered goat than did paired intact branches. Branches on living Acacia seyal plants that had their thorns removed suffered significantly greater herbivory by a wild population of free-ranging giraffes than did intact branches on the same plants. These differences in herbivory resulted in long term losses of branch length in clipped as opposed to control branches. In addition, branches within reach of giraffes produced longer thorns and a greater density of thorns than did higher branches. These results imply that increased thorn length is an induced defense.
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  • 7
    ISSN: 1432-1939
    Keywords: Acacia ants ; Giraffes ; Defense ; Myrmecophytes ; Crematogaster ; Thorns
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary We explore here the occurrence of aggressive ants in an apparently symbiotic relationship with the savanna tree Acacia drepanolobium and their effects on giraffe herbivory on the Athi-Kapiti Plains, Kenya. Trees taller than 1.3 m were more likely to be occupied by aggressive ants in the genus Crematogaster than were shorter trees. Ants wereconcentrated on shoot tips, the plant parts preferred by giraffes. Trees with relatively more foliage had more swarming ants than did trees with less foliage. The feeding behavior of individual freeranging giraffes on Acacia drepanolobium was studied. Giraffe calves exhibited a strong sensitivity to Crematogaster ants inhabiting A. drepanolobium, feeding for significantly shorter periods on trees with a greater number of aggressive ants. Older giraffes were apparently less sensitive to ants, and did not feed for shorter periods on trees with fuller foliage, despite significantly greater ant activity on these plants. The thorns of A. drepanolobium are significantly shorter than are the thorns of A. seyal, a species without symbiotic ants, a pattern that may indicate a trade-off between ants and thorns as defenses.
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Oecologia 58 (1983), S. 373-377 
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary A zone of C3−C4 grass overlap has been identified on the northern slopes of Mount Kenya at elevations of 2,800–3,200 m. At higher elevations, C3 grasses predominate; below, C4 grasses predominate. At each of three elevational sites of overlap, a series of transects was surveyed for C4 and C3 grass composition. All transects were located in structurally similar vegetation (high elevation grassland) within 150 m of each other. Transects were run in a variety of topographic situations. Within each transect, several environmental parameters were measured. Both unweighted (species presence/absence) and weighted (by frequency) measures of %C4 composition were significantly correlated with dry season soil moisture. Drier transects contain significantly more C4 species, in greater frequency, than wetter transects. Other correlations of C4 composition (e.g. factors which tend to parallel soil moisture) were also found. This local trend parallels the larger scale tendency of C3 grasses to replace C4 grasses with increasing elevation. Finer scale habitat partitioning may account for C3−C4 overlap within transects.
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Behavioral ecology and sociobiology 32 (1993), S. 377-385 
    ISSN: 1432-0762
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Activity patterns were documented over a 20-month period in six groups of vervet monkeys (Cercopithecus aethiops) in Amboseli National Park, Kenya. Group size varied both among groups and within groups through time. The home ranges of two groups were located in Acacia xanthophloea habitat whereas those of four adjacent groups were located in A. tortilis habitat. Repeated measures analysis of variance, three-way analysis of variance, and meta-analysis of group size effects were carried out on feeding, moving, resting, scanning, allo-grooming, and ‘other’ behavior. Time spent feeding varied seasonally, peaking during periods when A. tortilis seeds were eaten. However, time spent feeding did not vary within or among groups, or between habitats, males and females, or dominants and subordinates. Males spend more time scanning and less time allo-grooming than females, and high-ranking individuals of both sexes spent more time scanning than low-ranking individuals. Among females, subordinates spent more time moving, whereas among males, dominants spent more time moving. Groups living in A. xanthophloea habitat spent more time moving and allo-grooming than groups in A. tortilis habitat but this may have been confounded by the fact that these two groups were on average larger than the others. Significant differences in activity budgets among groups demonstrate that activity patterns observed in one group are not always readily generalized to other groups even when they come from the same population. Group size analyses examined potential costs and benefits of group living. Increased intragroup competition, measured by time spent moving and feeding, was only weakly evident in larger groups. Individuals in larger groups allo-groomed more than individuals in smaller groups. Self-grooming also increased in larger groups. Individuals in larger groups spent less time scanning than individuals in smaller groups, but there was more scanning per group in larger groups than in smaller groups.
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  • 10
    ISSN: 1432-0762
    Keywords: Key words Food resources ; Sympatry ; Dominance ; Intragroup aggression ; Group size
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The effect of food resources on behavior has been difficult to measure. Here we use animals themselves to describe “effective” food abundance and distribution by comparing, relative to where individuals stopped to eat, movements of (1) adult females living in a small group of vervet monkeys (Cercopithecus aethiops) with those living in a large group and (2) vervets and patas monkeys (Erythrocebus patas). Although females in the large vervet group travelled farther and stopped to eat more often than females in the small vervet group, these differences resulted from foraging in Acacia drepanolobium habitat. In A. xanthophloea habitat, females in the large group travelled less far, travelled shorter distances between foods, and stopped as often as females in the small group. Greater foraging costs of females in larger vervet groups may be offset by access to home ranges of better quality. Compared to patas, vervets travelled shorter distances, moved shorter distances between food sites, stopped less often, and had longer feeding bouts, suggesting that foods of vervets are denser and larger, overall, than foods of patas. When vervets foraged in A. drepanolobium habitat, also the habitat of patas, their foraging behavior became more like that of patas. Vervets travelled farther, stopped more often, and spent less time at food sites in A. drepanolobium habitat than in A. xanthophloea habitat, suggesting that foods are smaller and less usurpable in A. drepanolobium habitat. Distance between foods, a component of food distribution, did not increase, however. The critical variable underlying usurpability of foods may be food site depletion time, a temporal measure.
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