A nested vegetation sampling method which was developed by R.H. Whittaker for comparison of plant species diversity is described. The species richness of an area of 0.1 ha (1 dunam; 20 × 50 m) is analyzed by a special procedure in which different parameters of diversity such as differential diversity, point diversity, equibility and dominance are recorded. Normal supplementary observations such as plant coverage, growth forms, phenology and vertical foliage profile are added to the sample. By standardization of data collection for diversity samples, different plant communities from different regions of the world can be compared.
Avi Shmida and Reuven Dukas
We investigated the body size of solitary bee species in a Mediterranean plant community of Israel in relation to the seasonal increase in air temperature during the flowering season. We found that the body sizes of the species of solitary bees that are active from March to August are negatively correlated with the seasonal increase in air temperature. Also, the seasonal decrease in the body sizes of bees is correlated with a progressive decrease in the flower sizes of bee-pollinated species of the mint family that blossom each month.
NOAM LEVIN and AVI SHMIDA
With the current loss of biodiversity, efforts are being amassed to prioritize biodiversity hotspots that should receive high conservation priority. These studies often compare different biogeogrpahical regions using absolute estimates of species richness or rarity. Consequently, arid, semiarid, and other areas (e.g., boreal) are often ignored or are undervalued. Here, using a regional case study, we propose and demonstrate an approach that enables us to determine plant-based hotspots over landscape units across biogeographical regions using normalized, and comparing with absolute, measures. Three botanical variables were calculated for 521 predetermined landscape units in Israel. These included plant species richness, the sum of scores of red (endangered) species, and a spatial exclusiveness score, all calculated from the Israel Plant Information Center (Rotem) database. We classified the landscape units into six rainfall belts (from extreme-arid to mesic-Mediterranean), as a normalization method to enable comparison and ranking across different environments. Residuals from the species-area curves were calculated within each belt for each of the variables, as a means to normalize for sampling effects. The 25 highest-ranking landscape units were identified as botanic hotspots, both before and after normalization. Prior to normalization, most of the hotspots were located in the Mediterranean region. Following normalization, hotspots were identified across the entire climatic gradient and corresponded with threatened habitats where many threatened plant species exist, such as wetlands, sandy loamy soil, and heavy clayey soil areas. The use of rainfall belts enabled us to identify additional important conservation hotspots that are located in relatively poor species environments, such as deserts. This method should be further applied on a global basis to identify hotspots within additional biomes that have been mostly excluded from existing global hotspot maps, such as the Taiga, Boreal forests, Tundra, and the arid and semiarid desert and Xeric shrublands.
Tamar Keasar and Avi Shmida
Loss and fragmentation of foraging habitats, and extreme seasonality in the flowering phenology of wild plants, limit honeybee populations in Israel. This problem can be alleviated by the planting of bee forage plants in forests, parks, and along roadsides. To provide recommendations for such planting, we combined a literature survey and qualitative evaluations of experts to compile a list of 266 local wild plant species that have high food potential for bees. We also quantitatively evaluated the food potential of 32 species of trees and shrubs planted by Keren Kayemeth LeIsrael—Jewish National Fund (KKL—JNF). We recorded the following parameters of each species: main flowering season; flower morphology; type of food reward; number of flowers per plant; nectar standing crop; hourly nectar production rate; type of insect visitors; and frequency of insect visits. We ranked the surveyed species according to their potential importance as food plants, assigning high ranks to species that (a) bloom between July and February (the period of dearth in flowering natural vegetation), (b) produce large amounts of nectar, and (c) are highly attractive to honeybees. Of the species surveyed, Amygdalus communis, Eucalyptus camaldulensis, Ceratonia siliqua, and Ziziphus spina-christi best combined these benefits. A regression model indicated that high nectar production rates increased insect visitation rates, while long flowers reduced them, in an inter-specific analysis. Our study highlights the importance of diversified forestry planting to address agricultural, conservation, and recreational needs.
Lorne M. Wolfe and Avi Shmida
The major goal of this study was to examine patterns of gender variation in Ochradenus baccatus, a shrub found in the Judean Desert and Arava Valley of Israel, whose breeding system was previously considered dioecious (separate male and female individuals). We conducted detailed measurements on 150 marked plants over two years to (1) quantitatively describe the variation in sex expression and elucidate the factors responsible for gender variation in males, (2) determine the role of plant size in regulating the flowering behavior through the year, and (3) document pollinator visitation to males and females. The variability in sex expression differed between males and females. Females only reproduced by seed. In contrast, gender in males was extremely variable: 35% of males reproduced only by pollen donation (pure males) and 65% produced pollen and varying amounts of fruit and seeds (inconstant males). The ability to produce fruit was highly correlated with individual plant size. Inconstant males were significantly larger than pure males. Individual plant size also determined the flowering pattern through the year. Unlike most other desert plant species that typically flower after the winter rains, large O. baccatus plants flowered all year. Small plants, regardless of sex, flowered only during the winter months. The flowers of O. baccatus were visited by a diverse suite of insects including wasps, bees, ants, beetles, flies, and butterflies. Perhaps owing to the greater attractiveness of the floral display of males (due to the presence of yellow pollen), males were visited by many more insects than females. Over four observation days, 526 insects were counted on male plants compared to only 39 on females.
STEPHEN P. ELLNER and AVI SHMIDA
Inter- and intra-specific variations in seed dispersal in the genus Picris (Compositae) are reported and discussed in relation to mathematical theories of evolutionarily stable dispersal “strategies”. Two main trends are found: (1) seed dispersability is generally reduced in semi-arid and arid regions (compared with more mesic regions) by achene dimorphism in which marginal achenes are larger, lack a pappus, and are retained on the mother plant in unified involucral bracts; (2) dispersability is higher in arid than in semiarid regions, due to an increased frequency of wind-dispersal achenes in species restricted to desert washes. The latter trend is interpreted, on the basis of the mathematical theories, as an adaptation to the greater crowding and spatial variability of water availability in desert washes.
Gidi Ne’eman, Avi Shmida and Avi Perevolotsky
RONEN KADMON, AVI SHMIDA and REINHARD SELTEN
The behavior of bees foraging for nectar on Anchusa strigosa was studied. The flowers of this species are irregularly distributed in three-dimensional space, and the corolla is violet in young flowers and blue in mature ones. Blue flowers produced nectar at higher rates and received more visits per unit time than violet flowers, which indicates that the bees were able to associate reward with flower color. Before the beginning of bee activity, blue flowers contained more nectar than violet flowers, but during foraging activity they contained lower amounts of nectar. This reversal is inconsistent with predictions of optimal foraging theory. Bees tended to commence foraging at bottom flowers and worked predominantly upwards. Nectar standing crop was uncorrelated with flower height before foraging activity and either uncorrelated or positively correlated with flower height during foraging activity. We relate the positive correlations to the observed “movement rules” (bottom flowers were depleted more frequently than upper ones) and suggest that in both our study and some previous studies these rules reduced, rather than increased, the probability of finding nectar-rich flowers.
Ronen Kadmon and Avi Shmida
Theoretical studies suggest that fluctuations in availability of resources should lead to related fluctuations in the intensity of competition, and that significant competition should occur only in years of severe resource scarcity. This prediction has been supported by a number of studies conducted in animal populations, but has never been tested in plant populations. In this study, we performed neighbor removal experiments in conjunction with rainfall manipulation experiments, to test how fluctuations in rainfall, the major limiting resource for desert annuals, affect the intensity of competition in populations of the desert annual Stipa capensis. In order to test for the effect of spatial heterogeneity on the relationships between rainfall and competition intensity, populations were studied in three types of habitats: slopes, depressions, and wadis. Competition intensity was quantified, for each combination of habitat and rainfall, as the percentage of potential seed yield per germinating plant which was prevented due to competitive effects. Intensities of competition in the studied populations varied considerably between habitats, between seasons, and between rainfall manipulation treatments. In the most favorable habitat, the wadi, competition was always intense, independent of rainfall conditions. In the drier, slope and depressions habitats, natural and experimental changes in the amount of the yearly rainfall had considerable effects on competition intensity, but most pronounced competition was associated with high resource availability, a pattern which is opposite to the pattern that was predicted and documented for animal populations. The overall results suggest that competitive effects may have critical influence on the population dynamics of the species studied. This contradicts previous hypotheses on the relative importance of competition in desert plant populations.
MICHAEL G. BARBOUR, AVI SHMIDA, ANN F. JOHNSON and BOOKER HOLTON
Coastal dune scrub near Caesarea, Israel was quantitatively described from quadrats placed in 10 sites, ranging from pioneer to near-climax communities. Sampling intensity was greatest in a mixed shrub community (Artemisia monosperma, Helianthemum stipulation, Retama raetam) characteristic of stabilized dunes in the study area. Artemisia canopy had much less effect on the distribution of understory species than Retama and Helianthemum canopies. The sampled flora of 131 taxa was dominated by Leguminosae, Gramineae, and Compositae. About 45% of the flora had Mediterranean affinities, 17% coastal (mostly endemic to Israel), and 16% desert. California dune scrub from Point Reyes and Vandenberg areas was also sampled. The two sites are climatically similar to Caesarea, but both experience summer fog which lowers summer temperatures below those at Caesarea. Climax scrub was dominated by Lupinus arboreus and Haplopappus ericoides at Point Reyes, by H. ericoides associated with L. chamissonis, Core- throgyne filaginifolia, and Senecio blochmanae at Vandenberg. Its physiognomy was only superficially similar to the Caesarea mixed shrub: three canopy layers (shrubs 1 m tall + subshrubs + herbs); somewhat open (75% cover); perennial leaves typically soft, evergreen, small or dissected, and pubescent. In contrast to Israel, annuals contributed very little cover and stands were dominated instead by shrubs and chamaephytes. Sclerophylls and succulents were more common in California. One-third of the sampled 86 taxa were Compositae. About 37% of the flora had Mediterranean (=Californian floristic province) affinities and a similar fraction was strictly coastal. Only 6% had desert affinities and 14% were introduced. The percentage of endemism was 2–3 times higher in the Californian dunes. We concluded that the level of convergence attained by these two disjunct vegetation types was superficial, despite similarities in their present environments and physiognomies.