Enrique Jurado

Are nurse-protégé interactions more common among plants from arid environments?

Abstract Harsh conditions in arid and semi-arid environments make seedling establishment rare. Plant recruitment in arid environments often occurs only in years with above average rainfall or in safe sites under the canopy of nurse plants that provide shelter from high temperatures and low moisture. Associations of establishing seedlings with adult plants are referred to as nurse-protégé interactions and are thought to be commensalisms in which seedlings benefit from the micro-environment created by adult plants with no effect for the latter. This phenomenon is thought to be more frequent in harsh than in mild environments and appears to occur frequently in deserts and arid and semi-arid biomes. Here, we investigate whether nurse-protégé interactions are more common in arid environments by searching the published literature from the previous 92 years using the terms nurse plants, protégé plants, facilitation, nucleation and facultative mutualism. We then quantitatively compared these reports from arid zones to other environments. A total of 296 papers were found which referred to nurse-protégé interactions. More than half (158) focused on arid and semi-arid zones. This information was also used to explore hypotheses of potential causative forces that might have selected for such interactions in the arid zones such as seed trapping, nutrient, moisture, protection from browsing or trampling and support availability. Because of the large number of different nurse species (147, from 98 genera and 40 families) and protégé species (429, from 273 genera and 84 families), described across a diversity of environments, we suggest that there may be more than one causative factor selecting for nurse-protégé interactions in arid and semi-arid environments. Nomenclature: See references in (App. 1).

Seedling growth in relation to seed size among species of arid Australia

It has been reported that species from environments where seedlings are prone to drought during establishment tend to have larger seeds. One proposed reason for this is that larger-seeded species might be able to allocate a larger proportion of mass to roots rather than shoots during early growth. Seedlings of 32 species from arid central Australia were grown in coarse sand under standard conditions in a glasshouse, and harvested 10 days after germination. Seedlings from heavier-seeded species did not allocate relatively more resources to roots than lighter-seeded species. Complementary experiments confirmed this result for plants grown on sandy loam, in drying as compared to well-watered soil, and under shaded conditions (...)

Correlates of Seed Size Variation: A Comparison Among Five Temperate Floras

1 Five temperate floras were studied to assess to what extent seed size correlations with other plant attributes are consistent across floras. The floras were from three continents: Australia (semiarid woodlands of western New South Wales, arid woodlands of Central Australia, and the Sydney region), North America (Indiana Dunes) and Europe (Sheffield region, UK). The plant attributes used were growth form, plant height, perenniality and dispersal mode. We used general linear models to consider not only the primary correlations between seed size and each other attribute, but also the overlap patterns among correlations to determine if each correlation could be interpreted as a secondary effect via a third variable. 2 Plant height and growth form were consistently correlated with the largest proportion of log seed mass variation (up to 37% in Central Australia). Although there was strong overlap in the amount of log seed mass variation explained by the two attributes (6-22%), each could explain small but significant variation after the other in all floras. The strong association between growth form/plant height and seed size was found not only among unassisted and wind-adapted species, but also among species dispersed by other means. 3 In all floras, dispersal mode was also able to account for significant variation in log seed mass independently of growth form and plant height. The association between plant perenniality and seed size could be explained as a secondary correlation of growth form and plant height with both seed size and perenniality. 4 There were significant differences in log seed mass among the five floras. However, seed size ranged over at least five orders of magnitude in each flora. Differences between floras could account for relatively little (4%) of the variation in seed size between species, compared to the attributes growth form (20%), plant height (20%) and dispersal mode (29%), despite the quite different soils and climates of the five floras. This suggests that seed size is more strongly associated with other plant attributes than with the environmental conditions for establishment. It appears that within any one community, plants have found a diversity of possible solutions to the problems of seedling establishment, resulting in a wide range of log seed mass.

Convergence of elaiosomes and insect prey: evidence from ant foraging behaviour and fatty acid composition

1. Elaiosomes are lipid-rich appendages on the seeds of some plant species that promote dispersal of the seeds by ants. In this study we investigated the hypothesis that elaiosomes on seeds have converged in composition and attractiveness with the insect prey of ants. 2. The fatty acid compositions of 12 species of elaiosomes were compared to seeds of the same species and to seven orders of insects. The fatty acid compositions of the elaiosomes were more like those of insects than seeds; the levels of palmitic, palmitoleic, stearic and oleic acids in elaiosomes and insects were particularly similar. 3. The response of six ant species to the diglyceride 1,2-diolein was compared. This lipid is purported to be the principal attractant in elaiosomes and a review of the literature revealed that it is also an important component of insect haemolymph

Putting plant resistance traits on the map: a test of the idea that plants are better defended at lower latitudes

• It has long been believed that plant species from the tropics have higher levels of traits associated with resistance to herbivores than do species from higher latitudes. A meta-analysis recently showed that the published literature does not support this theory. However, the idea has never been tested using data gathered with consistent methods from a wide range of latitudes. • We quantified the relationship between latitude and a broad range of chemical and physical traits across 301 species from 75 sites world-wide. • Six putative resistance traits, including tannins, the concentration of lipids (an indicator of oils, waxes and resins), and leaf toughness were greater in high-latitude species. Six traits, including cyanide production and the presence of spines, were unrelated to latitude. Only ash content (an indicator of inorganic substances such as calcium oxalates and phytoliths) and the properties of species with delayed greening were higher in the tropics. • Our results do not support the hypothesis that tropical plants have higher levels of resistance traits than do plants from higher latitudes. If anything, plants have higher resistance toward the poles. The greater resistance traits of high-latitude species might be explained by the greater cost of losing a given amount of leaf tissue in low-productivity environments.

Diaspore Weight, Dispersal, Growth Form and Perenniality of Central Australian Plants

Diaspore weight and dispersal were measured in 229 plant species of the central Australian arid zone. The frequency distribution of log diaspore sizes was unimodal, as has been observed for other habitats. the quantity of reserve (embryon plus endosperm) stored in the seed was related to the weight of the dispersal unit. Reserve weight was greater for woody species than for herbaceous species. Within each growth form, there was no clear relationship between perenniality and reserve weight. Most graminoids were wind dispersed, and elaiosomes for and dispersal were more common among the woody species (...)

Spatial variations of interception loss components by Tamaulipan thornscrub in northeastern Mexico

Measurements of gross rainfall, throughfall and stemflow fluxes were conducted from April 1997 through April 1998 within a Tamaulipan thornscrub community in northeastern Mexico. Throughfall and stemflow fluxes represented 78.1% and 3.0% of gross rainfall, implying that interception loss from this community was 18.9%. Canopy water fluxes were often statistically different between study plots and these differences were largely explained by variations in plant dasometric characteristics. The revised Gash analytical model of rainfall interception loss was employed and simulated interception loss values were close to observed values. However, results from this study suggest that the parameters employed within the Gash analytical model are sensitive to spatially variable plant characteristics such as stem diameter, stem height and weighted leaf area index. This suggests that the transferability of the Gash model may be limited even within the same ecosystem unless the spatial variability of plant dasometric characteristics are taken into account.

Geographic ranges of plant species in relation to dispersal morphology, growth form and diaspore weight

We investigated the relationship of geographic range to growth form, dispersal morphology and diaspore weight within three comparative databases of 219-325 native species from arid central Australia, semi-arid western NSW and maritime Sydney. Geographic range was measured as the number of regions occupied. In the arid and semi-arid floras, but not in the maritime flora, species adapted for dispersal by vertebrates (mainly birds) tended to occupy more regions than species adapted for dispersal by other means. The same pattern occurred within four major families (Chenopodiaceae, Myoporaceae, Mimosaceae and Solanaceae), and thus was not a product of differences between families. We suggest that lineages with adaptations for long-range dispersal may have undergone a lesser incidence of geographic speciation, within the arid and semi-arid flora.

Leguminosas del norte del estado de Nuevo León, México

A study of the diversity of legumes in the northern part of the state of Nuevo Leon was undertaken. 38 genera, 94 species and 26 infraspecific taxa of legumes were recorded. The family Fabaceae comprises 18 genera and 42 species, Mimosaceae 10 and 30 and Caesalpiniaceae 10 and 22 respectivelly. The genera with highest number of species are Acacia (12), Dalea (10), Mimosa (6), Senna (5), Caesalpinia (4) and Bauhinia (4). Shrubby legumes are the most abundant in the zone, representing 47% (46 species); the herbaceous ones constitute 46% (45) and the arboreal ones comprise 7% (7). The highest number of taxa was recorded on semithorn shrubland (52) piedmont scrub (48), oak-pine forest (44), while the mezquite shrublands shelter the lowest number of species (23).

Seedling establishment under native tamaulipan thornscrub and Leucaena leucocephala plantation

Abstract In order to investigate the influence that plantations and clearing of native vegetation might have on plant regeneration in northeastern Mexico, seedling survival and germination (i.e., seedling emergence from the soil surface) were measured monthly in native fragments and an exotic plantation over a one-year period. Seedlings were measured in 1-m 2 plots, using 10 replicates under each of three different treatments: (i) dense thornscrub, (ii) semi-cleared thornscrub, and (iii) a dense L. leucocephala plantation. Seedling number peaked during summer and early autumn, lowest number of seedlings occurred during early spring. Excluding grasses, 36 species were present during the study, and only 14 were present in L. leucocephala plantation. Thornscrub and open thornscrub had similar number of grass seedlings, whereas more forb seedlings were present in open thornscrub. Seedlings of woody species were similar for all treatments. Under L. leucocephala germination was low for most species other than itself, most seedlings, however, died during the winter months.