Francisco M. Azcárate

Seed size, shape and persistence in dry Mediterranean grass and scrublands

Seed size and shape, measured as the variance of the three main dimensions, have been proposed as good indicators for predicting seed persistence. We tested whether these variables were robust predictors of seed persistence in the soil for 58 abundant herbaceous species, primarily annuals, in grass and scrubland of central Spain. Seed persistence was estimated from data on germinable seed banks, while seed weight and shape were measured using fresh seeds collected in the study area. There was a significant tendency for species with persistent seeds to have smaller seeds than species with transient seeds. Seed shape was not, however, related to persistence and we did not find any clear seed weight/shape threshold for predicting persistence. The binary logistic model of seed bank type as a function of seed weight was significant and explained 67% of total variability. Supplementary information about dormancy, environmental conditions of habitat, predation and attack by pathogens has to be used to elaborate more accurate general predictive models of seed persistence.

Handbook of protocols for standardized measurement of terrestrial invertebrate functional traits

Summary 1. Trait-based approaches are increasingly being used to test mechanisms underlying species assemblages and biotic interactions across a wide range of organisms including terrestrial arthropods and to investigate consequences for ecosystem processes. Such an approach relies on the standardized measurement of functional traits that can be applied across taxa and regions. Currently, however, unified methods of trait measurements are lacking for terrestrial arthropods and related macroinvertebrates (terrestrial invertebrates hereafter). 2. Here, we present a comprehensive review and detailed protocol for a set of 29 traits known to be sensitive to global stressors and to affect ecosystem processes and services. We give rec- ommendations how to measure these traits under standardized conditions across various ter- restrial invertebrate taxonomic groups. 3. We provide considerations and approaches that apply to almost all traits described, such as the selection of species and individuals needed for the measurements, the importance of intraspecific trait variability, how many populations or communities to sample and over which spatial scales. 4. The approaches outlined here provide a means to improve the reliability and predictive power of functional traits to explain community assembly, species diversity patterns and ecosystem processes and services within and across taxa and trophic levels, allowing compar- ison of studies and running meta-analyses across regions and ecosystems. 5. This handbook is a crucial first step towards standardizing trait methodology across the most studied terrestrial invertebrate groups, and the protocols are aimed to balance general applicability and requirements for special cases or particular taxa. Therefore, we envision this handbook as a common platform to which researchers can further provide methodological input for additional special cases.

Abundance and habitat segregation in Mediterranean grassland species: the importance of seed weight

Abstract We analysed the relationship between seed traits (weight, shape and dispersal structures) and the abundance and habitat segregation of Mediterranean grassland species. To take into account possible correlations with other plant traits, the study also includes 5 vegetative traits (growth form, plant longevity, clonality, onset of flowering and plant size) of commonly accepted functional importance. Data were recorded for 85 species from dehesa grasslands in central Spain. Species abundance was measured in upper (dry and less productive, high stress) and lower (moist and more productive, low stress) slope zones in the same area. Habitat segregation was estimated using an index based on the relative frequencies of species in upper and lower slope zones. Multiple regression models were fitted using species, as well as phylogenetically independent contrasts, as data points. Annual small-seeded species without specialised dispersal structures are over-represented in dehesa grasslands. Abundance was negatively related to seed weight in upper slope zones. None of the recorded plant traits were related to abundance in the lower slope zones. Habitat segregation was mainly related to seed weight, but also to some vegetative traits. Annual, early flowering and small-seeded species were relatively more abundant in the upper than the lower slope zones. This pattern is independent of phylogeny. Our results suggest that in dry Mediterranean grasslands, abundance of many species is determined by dispersal (production of numerous small seeds) rather than by competitive ability. Abbreviations: CSA = Cross species analysis; PIA = Phylogenetically independent analysis; PIC = Phylogenetically independent contrast. Nomenclature: Castroviejo (1986–1999), except taxa yet to be covered which follow Tutin et al. (1964–1980).

Spatial patterns of seed predation by harvester ants (Messor Forel) in Mediterranean grassland and scrubland

Summary. Seed predation by harvester ants is one of the main processes involved in the seed bank dynamics of Mediterranean grassland and scrubland. We investigated the spatial patterns of seed predation by Messor spp. in these systems from a multi-level approach (nest-site selection, foraging patch selection and seed predation risk), using ten experimental plots (20 m × 40 m) set in central Spain. All habitats in grasslands are dominated by M. barbarus, while in scrubland this species shares seed exploitation with M. bouvieri. In this type of system, the nest-hole and foraging territory distribution of the two species show a certain degree of segregation. Messor bouvieri focuses on the exploitation of dry scrub, while M. barbarus also forages on subhumid and humid patches. We interpret this as a consequence of the different foraging behaviour and nest site requirements of the two species. In general, the spatial distribution of seed predation risk reflects the patterns detected for the nest-holes and foraging areas, although scrubland has a more heterogeneous predation pattern than grassland.

Microclimatic Conditions Regulate Surface Activity in Harvester Ants Messor barbarus

This paper analyses the effect of microclimatic factors (internal soil temperature, surface temperature and surface relative humidity) on surface activity of Messor barbarus harvester ants. We selected 44 colonies in an area of Mediterranean grassland near Madrid (Central Spain), which were monitored for activity between March 1998 and September 1999. Results indicate that microclimatic factors are good predictors of colony activation and intensity of activity. Colonies became active above certain critical values of internal soil temperature and relative humidity. For active colonies, surface temperature was the main regulatory factor for worker departure rate, which peaked at around 25–30°C. Worker speed was positively correlated with surface temperature, although the relationship was weaker for large-sized workers. Microclimatic factors were not enough, however, to predict task allocation outside the nest. The explanation for this aspect of ant behavior probably requires the inclusion of biotic factors in the models.

From what depth do seeds emerge? A soil seed bank experiment with Mediterranean grassland species

Seed germination and emergence are influenced by the position of seeds in the soil bank profile. Mediterranean grasslands are heavily dependent on seed banks, as these systems are mainly composed of annual species. Seed bank germination experiments in a greenhouse were conducted to analyse the role played by burial depth on seed bank dynamics in annual Mediterranean grasslands. Specifically, they addressed two objectives: (1) to assess the ability of seeds in the shallow layer of the soil bank to emerge when they are buried at different depths, and (2) to ascertain the ability of seeds from deep layers to germinate and emerge to the surface. The study also produced a depth profile of species and seeds. The results show that: (1) all species (100%) and the majority of viable seeds (98.9%) are situated in the first centimetre, with a significant fall in the number of species and seeds in the soil bank as depth increases; (2) for the majority of species (92%) and seeds (85.4%) in the shallow bank, the emergence percentage declines significantly with burial depth; and (3) seeds that are present in deep layers need to rise to the surface in order to produce seedlings. In conclusion, the function of the seed bank in Mediterranean grasslands depends on the number of species and seeds in it, but also on the seed position in the profile and vertical movements that enable them to reach the surface.

The fate of seeds in Mediterranean soil seed banks in relation to their traits

Abstract Question: Is there any change in seed density and species richness in Mediterranean surface soil banks during summer? Are there any relationships between these summer variations and seed traits (weight, length and shape), without and with controlling the phylogenetic effect? Location: Central Spain. Methods: Samples of the surface soil seed bank were collected in two Mediterranean systems, grassland and scrubland, at two points in the year: immediately after the summer production peak and immediately prior to the autumn germination peak. We used Canonical Correspondence Analysis ordination to check for changes in floristic composition and ANOVAs to check for changes in seed density and species richness between summer and autumn samples. We used multiple regression analysis to analyse the relationship between summer variations in soil seed density and form traits, with and without controlling phylogenetic relations. Results: Soil seed density dropped significantly during the summer in the two systems (28% in grasslands, repeated measures ANOVA test; F = 58.19, P < 0.01; 72% in scrublands, repeated measures ANOVA test; F = 75.67, P < 0.001). Species richness, however, only dropped significantly in the scrubland (32%; repeated measures ANOVA test; F = 9.17, P < 0.05). Variation in the floristic composition of the shallow banks was only significant in the scrubland. Changes in shallow bank density were related significantly to seed morphology features, with greater drops in species with heavier seeds in grasslands and species with longer seeds in scrubland. Conclusions: Our results show a substantial loss of seeds in the uppermost soil layer during the summer period between the point of peak production and the autumn germination peak. This drop was clearer in the scrubland than in the grassland. Longer and/or heavier seeds underwent the greatest declines in density at the end of summer, indicating a more intense effect of post-dispersal predation on large-seeded species. Abbreviations: CSA = Cross-species analysis; PIA = Phylogenetically independent analysis; PIC = Phylogenetically independent contrast.

Effects of seed predation by ants on Mediterranean grassland related to seed size

Abstract Questions: 1. Do harvester ants (Messor barbarus) promote seed mortality in Mediterranean grassland?; 2. Is this effect greater in large-seeded species? Location: Central Spain. Methods: We established an ant-exclusion experiment of five circular (1.5 m diameter) plots from where ants were excluded during one year, along with ten control plots. We recorded the seed bank of all species in the plots both before and after the treatment. The effect of seed length and weight was analysed after transforming data into phylogenetically independent contrasts, and alternatively by dividing the species data set into morphological groups. Results: Longer and heavier seeded species significantly increased in the seed banks under the exclusion treatment, although ants did not significantly modify overall seed densities. Conclusions: Although the ants do not collect large numbers of seeds, they differentially affect the composition of the seed banks by selecting the longest or heaviest seeds, or both. The persistence of this short-term effect in the seed bank may result, over a number of years, in the system evolving towards a predominance of small-seeded annuals, congruent with the species composition actually observed in Mediterranean grasslands. Abbreviations: PIC = Phylogenetically independent contrast. Nomenclature: Castroviejo (1986–2005), except in the taxa yet to be covered which are named following Tutin et al. (1964–1980).

More for less: sampling strategies of plant functional traits across local environmental gradients

Summary Ecologists use approaches based on plant functional traits to tackle several fundamental and applied questions. Although a perfect characterization of functional trait structure requires the measurement of all the individuals in communities, this is prohibitively resource-consuming. Consequently, the general practice is to average the trait values of a reduced number of individuals per species. However, there are different alternatives regarding the number, identity and spatial location of the individuals chosen to calculate species-averaged trait values. In this study, we compared different strategies for sampling functional traits, using community-weighted mean trait values (CWM) and the Rao index of functional diversity (FD). We intensively sampled the functional trait structure along a topographical gradient in a Mediterranean grassland, obtaining accurate estimations of the ‘real’ values of these indices (CWMI and FDI) for three traits (height, leaf area and specific leaf area). We simulated three different sampling strategies differing in the spatial location of the individuals used to estimate species-mean trait: (i) average of the whole gradient (GLO), (ii) average of the sampling unit in which the abundances of species maximize (MAX) and (iii) average of a reduced number of individuals per species and sampling unit (LOC). For each strategy, we simulated different sampling intensities (number of individuals sampled). For each trait, we examined the ability of each strategy and sampling intensity to accurately estimate CWMI and FDI, as well as their ability to detect changes in functional trait structure along the topographical gradient. LOC outperformed the other strategies in terms of accuracy and bias, and was much more efficient to describe changes along the gradient, regardless of the traits and indicators considered. Furthermore, LOC was the only strategy that improved consistently as sampling intensity increased, especially at low levels of intensity. Our results indicate that the impact of considering intraspecific variability in trait values can be greater than commonly assumed. Strategies that neglect this source of variability can result in inaccurate or biased estimations of the functional trait structure of plant communities. Most importantly, we show that intraspecific variability can be taken into consideration without any increases in the total number of individuals measured.

Abandonment of grazing in a mediterranean grassland area: consequences for ant assemblages

Abstract.  1. Abandonment of traditional activities in the rural areas is widespread in the developed world, and in the case of grazing, it is known to have negative consequences on the diversity of plant communities. Few studies have examined the impact of grazing abandonment on fauna, which in the case of ants is of considerable interest, given their usefulness as an indicator for monitoring environmental change.