Teresa Navarro

Quantitative characterization of the regressive ecological succession by fractal analysis of plant spatial patterns

We studied the effect of grazing on the degree of regression of successional vegetation dynamic in a semi-arid Mediterranean matorral. We quantified the spatial distribution patterns of the vegetation by fractal analyses, using the fractal information dimension and spatial autocorrelation measured by detrended fluctuation analyses (DFA). It is the first time that fractal analysis of plant spatial patterns has been used to characterize the regressive ecological succession. Plant spatial patterns were compared over a long-term grazing gradient (low, medium and heavy grazing pressure) and on ungrazed sites for two different plant communities: A middle dense matorral of Chamaerops and Periploca at Sabinar-Romeral and a middle dense matorral of Chamaerops, Rhamnus and Ulex at Requena-Montano. The two communities differed also in the microclimatic characteristics (sea oriented at the Sabinar-Romeral site and inland oriented at the Requena-Montano site). The information fractal dimension increased as we moved from a middle dense matorral to discontinuous and scattered matorral and, finally to the late regressive succession, at Stipa steppe stage. At this stage a drastic change in the fractal dimension revealed a change in the vegetation structure, accurately indicating end successional vegetation stages. Long-term correlation analysis (DFA) revealed that an increase in grazing pressure leads to unpredictability (randomness) in species distributions, a reduction in diversity, and an increase in cover of the regressive successional species, e.g. Stipa tenacissima L. These comparisons provide a quantitative characterization of the successional dynamic of plant spatial patterns in response to grazing perturbation gradient.

Translational and Fluctuating Asymmetry as Tools to Detect Stress in Stress‐Adapted and Nonadapted Plants

Plants having experienced previous exposure to a stress are expected to be more resistant to further stress than those not having been exposed. While the assessment of stress in plants is a difficult task, particularly for stress‐adapted plants, developmental instability has proven a useful tool for assessing stress in organisms. We examined the effect of water availability on developmental instability (translational asymmetry and fluctuating asymmetry) and growth of Anthyllis cytisoides L. under a precipitation gradient. We compared A. cytisoides in very xeric (Almería, 256 mm of average rainfall) and subhumid (Málaga, 613 mm of average rainfall) areas, from north‐ and south‐facing slopes, after both a period of extreme drought (1995) and a humid period (1997). Translational symmetry varied between north‐ and south‐exposed plants but differently for the Almería and Málaga populations. We observed that developmental stability was enhanced in south‐exposed plants in the population from the more xeric habitat (Almería) after both dry and humid periods. In contrast, A. cytisoides living in a subhumid habitat did not alter their developmental stability in response to exposure after a humid period but exhibited a decline in stability in south‐exposed slopes after a dry period. That is interpreted as a consequence of the adaptation of A. cytisoides to aridity. Growth patterns were also investigated. By reducing growth, plants can mitigate stress through a reduction of water and nutrient demands, allowing the maintenance of a steady supply of nutrients for developmental stability. This strategy was followed by plants acclimated to drought. But in mild weather, such as that of Montes de Málaga, a high growth rate cannot be supported when water is scarce. We also observed that floral fluctuating asymmetry was greatest on north‐facing slopes at both the Almería and Málaga sites. That is, southern exposure enhanced floral homeostasis during development. Additionally, comparisons between translational and fluctuating asymmetry showed that translational asymmetry is more sensitive to environmental change than fluctuating asymmetry.

Developmental instability in gynodioecious Teucrium lusitanicum

Developmental instability was assessed in two geographical races of Teucrium lusitanicum using morphometric measures of vegetative and reproductive structures. T. lusitanicum is a gynodioecious species. Male sterile (female) individuals showed greater developmental instability at all sites. Plants located inland had higher developmental instability of vegetative characters and lower developmental instability of reproductive characters than coastal plants. These results support the contentions that (1) developmental instability is affected more by the disruption of co-adapted gene complexes than by lower heterozygosity, and (2) different habitat characteristics result in the differential response of vegetative and reproductive structures.

Geographical Variation and Successive Adaptive Radiations of Yellow-Flowered Teucrium (Labiatae) in the Mediterranean Region

Study of the geographical variation of yellow-floweredTeucrium sect.Polium species using morphological, chemical, and cytological analyses shows that the group of North African taxa is both differentiated from the European group and homogeneous with it. It displays stable vegetative and floral characters that are common to all the taxa. The essential differences concern the indumentum structure and the habit of the plants. The diversity of environments has enhanced the expression of successive radiations of the group. The first doubtless originated in the Betic-Rif zone and in particular in the southeastern part of the Iberian Peninsula. These radiations probably first gave the groupT. aureum, now endemic in the Ibero-Provençal mountains. The species then became better differentiated in North Africa. Differentiation took place in the mountain ranges (Rif, Atlas, and Hoggar) and some Mediterranean islands (off the eastern coast of Tunisia) for the current species with narrow endemism and in desert regions (steppes and the Sahara) for those with wider endemism.

Leaf patterns, leaf size and ecologically related traits in high Mediterranean mountain on the Moroccan High Atlas

Leaf traits functional relationship is particularly important in plant ecological strategies, but few data are available from Mediterranean high-altitude environments. We analysed leaf general patterns and leaf trait relationships in 84 perennial species on the High Atlas, Morocco. We examined the correlation amongst leaf size, leaf width and length, plant height and seed size, analysed multi-trait relationships using Structural Equation Models and tested leaf size variation amongst growth forms (functional groups). Species spanned 103 range of leaf size (sub-lepto- to microphylls). Nanophylls (48.8%) were dominant and over-represented in half-shrubs. Tree and rosette herbs were more likely to have large leaf size (nano-micro- and microphylls), whereas shrubs have medium leaf size (nano-micro- and nanophylls) and cushion and half-shrubs have small (sub-lepto- to nanophylls) and narrow leaves. Small-leaved species synchronized their leaf phenological activity with the dry summer months (May–August), and large-leaved species extended throughout the spring until the end of summer following the similar patterns found in lowland Mediterranean environments. Regarding woody species, our results showed a positive and significant relationship between leaf size and plant height and a non-significant relationship between leaf size and seed size. Structural Equation Models showed that variation in leaf size was triggered chiefly by changes in leaf form (leaf width) and plant height, seed size being of no relevance. In our study area, large-seeded species have a relatively wide range of leaf size. The hypothesis that the combination of large seeds and small leaves is allometrically unlikely (except for leptophyll Conifers) was supported in this study.

Inferring resilience to fragmentation-induced changes in plant communities in a semi-arid Mediterranean ecosystem.

Predicting the capacity of ecosystems to absorb impacts from disturbance events (resilience), including land-use intensification and landscape fragmentation, is challenging in the face of global change. Little is known about the impacts of fragmentation on ecosystem functioning from a multi-dimensional perspective (multiple traits). This study used 58 500-m linear transects to quantify changes in the functional composition and resilience of vascular plant communities in response to an increase in landscape fragmentation in 18 natural scrubland fragments embedded within a matrix of abandoned crop fields in Cabo de Gata-Níjar Natural Park, Almería, Spain. Changes in functional community composition were measured using functional diversity indices (functional richness and functional dispersion) that were based on 12 plant traits. Resilience was evaluated using the functional redundancy and response diversity from the perspective of plant dispersal, which is important, particularly, in fragmented landscapes. Scrubland fragmentation was measured using the Integral Index of Connectivity (IIC). The functional richness of the plant communities was higher in the most fragmented scrubland. Conversely, the functional dispersion (i.e., spread) of trait values among species in the functional trait space was lower at the most fragmented sites; consequently, the ecological tolerance of the vegetation to scrubland fragmentation decreased. Classifying the plant species into four functional groups indicated that fragmentation favoured an increase in functional redundancy in the ‘short basal annual forbs and perennial forbs’ group, most of which are species adapted to degraded soils. An assessment based on the traits associated with plant dispersal indicated that the resilience of ‘woody plants’, an important component in the Mediterranean scrubland, and habitat fragmentation were negatively correlated; however, the correlation was positive in the ‘short basal annual forbs and perennial forbs’ and the ‘grasses’ groups.

Narrow endemics of the Almeria Province (Andalusia, Spain) differ in their traits and ecological niche compared to their more widespread congeners

Understanding the evolutionary ecology of geographically restricted species is of great importance for the design of conservation strategies and for gaining insight into the evolutionary processes involved in the origin and maintenance of those species. With a very high proportion of endemic species and/or subspecies, the province of Almeria in Andalusia (SE Spain) represents a prominent hotspot of plant diversity in the Mediterranean Basin. In this paper, we use phylogenetically independent contrasts to examine whether narrow endemics (i.e. species mostly restricted to the Almeria Province, hereafter NE) have evolved a ‘syndrome of endemism’. Based on published trait values, we tested whether (i) NE occupy a particular altitudinal range, possess a smaller niche breadth and occur within particular plant associations, and whether (ii) NE have distinct vegetative and reproductive traits. We found that, compared to their more widespread congeners, NE (i) occupy a narrower altitudinal range at the upper or lower limits of their congeners’ ranges; (ii) occur in a smaller number of plant communities that are distinct from the communities of widespread species; and (iii) have an 11 % shorter flowering duration, 28 % fewer flowers per inflorescence, 30 % reduced floral display, and 23 % lower floral attractiveness. These differences are not explained by a smaller size overall or a different ploidy level. NE have apparently evolved traits that promote selfing. The shift towards higher selfing rates is interpreted as a mechanism to promote reproductive assurance and to decrease gene flow from the more widespread congeners.

Seed mass and germination traits relationships among different plant growth forms with aerial seed bank in the sub-tropical arid Arabian deserts

ABSTRACT Background: Seed mass and plant growth forms can affect dispersal syndrome that determines where seed is stored until germination, which can consequently determine germination requirements and the fate of emerged seedlings. Aims: This study aimed to assess the relationships between seed mass, germination rate and light and temperature requirements during germination of 23 desert plants with an aerial seed bank. Methods: Freshly collected seeds and those stored for 9 months at room temperature and enclosed within plant parts in the field were germinated in three growth chambers adjusted to three temperatures and two light regimes. Results: Trees and shrubs had significantly heavier seeds with greater dormancy compared to herbs. Germination at all storage conditions responded positively to light in herbs and germinated in both light and dark in shrubs and trees. Field storage enhanced light germination in trees, but not in shrubs and herbs. Germination rate index was greater for seeds of herbs and trees compared to those of shrubs. The relationships between seed mass and final germination in both light and dark regimes were positive in herbs but negative in shrubs. Conclusions: Growth form, seed size, storage condition can affect light, but not temperature, requirement of the studied plants.