The influence of host plant genotype on variation in population densities of the gorse thrips,Sericothrips staphylinus (Thysanoptera: Thripidae), and its consideration in relation to release strategies

Large variations in population densities of Sericothrips staphylinus were observed between gorse bushes at a field site in an earlier Tasmanian study. A replicated potted plant experiment was conducted to assess whether genetic variation between gorse bushes could affect densities of S. staphylinus. There were significant differences in the number of S. staphylinus recovered from the individual bushes sampled within sites and individual bushes across all sites. This provides evidence that genetic variation between gorse bushes is at least partly responsible for the observed variability in field populations. The result validates the current release strategy used for the field establishment of S. staphylinus in south-eastern Australia. This strategy involves making multiple small releases (ca. 250 adults per bush per site) instead of a small number of large releases (ca. 1000 per bush per site), thereby reducing variation in numbers due to genetic affects. Genetic variation between individual plants of the same species and associated effects on herbivore densities should be considered when devising release strategies for biological control agents.     

Impacts of defoliation by tussock moths (Orgyia vetusta) on the growth and reproduction of bush lupine (Lupinus arboreus)

Abstract.

• 1 Outbreaks of tussock moths (Orygia verusta Bdv.) on bush lupines (Lupinus arboreus Sims) may be very intense, although spatially localized, and may last >10 years. To understand better how such outbreaks may persist, we defoliated lupine bushes using variable realistic numbers of tussock moth larvae, and measured the immediate and delayed impacts of defoliation on the growth and seed production of lupine bushes.
• 2 Immediate effects of defoliation included the production of new leaves that were significantly smaller in diameter and biomass, and lower in water content, than the new leaves of undamaged bushes. Also, seed output was reduced by up to 80% on heavily damaged bushes.
• 3 In the longer term, surviving bushes recovered remarkably well, despite having received the full range of possible (survivable) insect densities. After 1 or 2 years’rapid growth, surviving bushes were not affected in terms of height, basal stem diameter or volume by their previous defoliation. However, there was a significant tendency for juvenile bushes to produce more seeds the more heavily they had been attacked the previous year.
• 4 The ability of the host plant to recover, in terms of its biomass, helps to explain the sustained nature of the insect outbreak.

     

Explaining variability in the production of seed and allergenic pollen by invasive <Emphasis Type="Italic">Ambrosia artemisiifolia</Emphasis> across Europe

To better manage invasive populations, it is vital to understand the environmental drivers underlying spatial variation in demographic performance of invasive individuals and populations. The invasive common ragweed, Ambrosia artemisiifolia, has severe adverse effects on agriculture and human health, due to its vast production of seeds and allergenic pollen. Here, we identify the scale and nature of environmental factors driving individual performance of A. artemisiifolia, and assess their relative importance. We studied 39 populations across the European continent, covering different climatic and habitat conditions. We found that plant size is the most important determinant in variation of per-capita seed and pollen production. Using plant volume as a measure of individual performance, we found that the local environment (i.e. the site) is far more influential for plant volume (explaining 25% of all spatial variation) than geographic position (regional level; 8%) or the neighbouring vegetation (at the plot level; 4%). An overall model including environmental factors at all scales performed better (27%), including the weather (bigger plants in warm and wet conditions), soil type (smaller plants on soils with more sand), and highlighting the negative effects of altitude, neighbouring vegetation and bare soil. Pollen and seed densities varied more than 200-fold between sites, with highest estimates in Croatia, Romania and Hungary. Pollen densities were highest on arable fields, while highest seed densities were found along infrastructure, both significantly higher than on ruderal sites. We discuss implications of these findings for the spatial scale of management interventions against A. artemisiifolia.     

Mammalian seed dispersal in Cantabrian woodland pastures: Network structure and response to forest loss

We evaluated the role of wild large mammals as dispersers of fleshy-fruited woody plants in woodland pastures of the Cantabrian range (N Spain). By searching for seeds in mammal scats across four localities, we addressed how extensive seed dispersal was in relation to the fleshy-fruited plant community, and applied a network approach to identify the relative role of mammal species in the seed dispersal process. We also tested the response of mammalian dispersers to forest availability at increasing spatial scales. Five carnivores and three ungulates dispersed seeds of eight fleshy-fruited trees and shrubs. Mammalian seed dispersal did not mirror community-wide fruit availability, as abundant fruiting trees were scarce whereas thorny shrubs were over-represented among dispersed species. The dispersal network was dominated by bramble (Rubus ulmifolius/fruticosus), the remaining plants being rarer and showing more restricted disperser coteries. Fox (Vulpes vulpes), badger (Meles meles), and wild boar (Sus scrofa) dispersed mostly bramble, whereas martens (Martes sp.) dispersed mostly wild rose (Rosa sp.). Ungulates occasionally dispersed holly (Ilex aquifolium) and hawthorn (Crataegus monogyna). The empirical network reflected a skewed distribution of interactions and some functional complementarity (as judged from the low levels of connectance and nestedness), but also some degree of specialization. Mammals overused uncovered microsites for seed deposition, and increased their disperser activity in those landscape sectors devoid of forest. Combined with previous findings on avian seed dispersal, this study suggest a strong functional complementarity coming from the low overlap in the main plant types that mammals and birds disperse – thorny shrubs and trees, respectively – and the differential patterns of seed deposition, with mammals mostly dispersing into deforested areas, and birds into forest-rich landscapes.     

Fire increases aboveground biomass,seed production and recruitment success of Molinia caerulea in dry heathland

During the last decades, the perennial tussock grass Molinia caerulea has shown an increased abundance in European heathlands, most likely as a result of increased nitrogen deposition and altered management schemes. Because of its deciduous nature, Molinia produces large amounts of litter each year, which may affect the intensity and frequency of accidental fires in heathlands. These fires may influence plant population dynamics and heathland community organization through their effects on plant vital attributes and competitive interactions. In this study, fire-induced changes in competitive ability and invasiveness of Molinia through changes in biomass production, seed set and seed germination under both natural and laboratory conditions were investigated. We found that fire significantly increased aboveground biomass, seed set and germination of Molinia. Seed set was twice as high in burned compared to unburned heathland. Two years after fire, seedling densities in natural conditions were on average six times higher in burned than in unburned heathland, which resulted in increased abundance of Molinia after burning. The seed germination experiment indicated that seeds harvested from plants in burned heathland showed higher germination rates than those from unburned heathland. Hence, our results clearly demonstrate increased invasive spread of Molinia after large and intense fires. Active management guidelines are required to prevent further encroachment of Molinia and to lower the probability of large fires altering the heathland community in the future.     

舟山市种子植物物种多样性及其分布特征

通过野外调查和查阅文献资料,分析了舟山市种子植物物种组成、区系特点及物种多样性的分布特征。结果表明:舟山市共有野生种子植物1372种,隶属于141科627属;植物区系组成以小型科属为主,生活型以草本植物居多,地理成分广泛而多样,滨海特有植物较多,重点保护植物较少;在10个典型岛屿中,物种丰富度及物种密度的分布极不均匀,南部岛屿的物种丰富度及物种密度相对较高,北部岛屿相对较低;在8种主要森林群落类型中,乔木层、灌木层、草本层中物种丰富度最高的分别是红楠林、香樟林、滨柃灌丛,物种丰富度、Simpson指数和Shannon-Weaver指数表现为灌木层乔木层草本层,Pielou均匀度指数在乔木群落中变化趋势不明显,但在灌丛群落中呈现草本层灌木层的规律。本文通过对舟山市种子植物物种多样性的调查分析,为舟山群岛野生植物资源的研究和保护积累了基础材料,为海岛植物资源的开发和利用提供了理论依据。     

Directed vertebrate-mediated seed dispersal of a fleshy-fruited amaryllid in a heterogenous habitat

Most plants with fleshy fruits have seeds that are ingested by animals, but a less well-understood mode of seed dispersal involves fleshy fruits containing seeds that are discarded by frugivorous animals because they are too large or toxic to be ingested. We studied the seed dispersal biology of Haemanthus deformis, an amaryllid lily species found in a mosaic of bush clumps in a grassland matrix in South Africa. We asked whether seed dispersal is directed in and among bush clumps and whether germination and survival are greater for seeds dispersed to bush clumps than for those dispersed into grassland. Using camera trapping, we found that fruits are consumed mainly by birds and rodents. The pulp was removed from the seeds which were then discarded without ingestion. While many seeds were dispersed close to the parent plant, most (c. 78.5%) were dispersed further than 1 m away from the parent plant. Longer distance dispersal resulted mainly from birds flying off with fruits in their bill or from rodents engaging in scatter-hoarding behavior. Seedling survival was most successful within bush clumps as compared to grasslands and shade was identified as a primary requirement for seedling survival. Seeds from which the fruit pulp had been removed germinated faster than those in intact fruits. Haemanthus deformis deploys a system of directed seed dispersal, whereby both birds and rodents contribute to the dispersal of seeds within patchy bush clumps that are favorable for seedling survival.     

Effects of trichomes on the behavior and distribution of Platyprepia virginalis caterpillars

Trichomes are an important physical resistance mechanism of plants, as they reduce insect herbivore movement, feeding, and digestion. However, we know little about how trichomes influence herbivore distributions and populations. We conducted laboratory and field experiments to evaluate the preferences of Platyprepia virginalis (Boisduval) (Lepidoptera: Arctiidae) caterpillars to natural and manipulated densities of trichomes on their primary food, Lupinus arboreus Sims (Fabaceae). We then conducted field surveys to determine whether variation in trichome density among lupine bushes affected caterpillar spatial distribution on the landscape. Platyprepia virginalis caterpillars preferred lupine leaves with fewer trichomes in choice and no‐choice experiments. In the field, caterpillar feeding damage was found more often on leaves with fewer trichomes. These preferences scaled up to the level of bushes in the landscape such that more caterpillars were found on bushes with lower trichome densities than on bushes with higher trichome densities. This is one of few studies to show the potential for trichome density to influence herbivore population size and distribution in a natural system at a landscape level. The results are consistent with trichomes functioning as a resistance mechanism with consequences for herbivore choice, performance, and distribution.     

Bush selection along foraging pathways by sympatric impala and greater kudu

In order to identify the selection mechanism of two sympatric African browsers, we analysed encounter rates and selection of bushes along foraging pathways. We monitored the tracks, left overnight, by kudu and impala on an experimental plot of natural Acacia nilotica and Dichrostachys cinerea in the highveld of Zimbabwe, and recorded the number of bushes attacked in each category. Both ungulates were selective for the bush categories, but kudu were consistently more selective than impala, and showed a higher preference for the larger A. nilotica and D. cinerea bushes, which had a significantly greater number of bites which were not reachable by impala. For both kudu and impala, the probability of attacking larger bushes increased significantly with the proportion of large bushes encountered along the foraging pathways, whereas the consumption of smaller bushes was apparently unpredictable. For the most abundant food item (medium D. cinerea), the probability of attack by impala along a pathway decreased with increasing proportions of larger bushes in the experimental area, but was also dependent on impala group size and season. In addition, we found that encounter rates with larger bushes were significantly higher for kudu than for impala. Experimentally reducing the availability of the larger bushes had little effect on both impala and kudu during the following rainy season. However, during the following cool dry season, kudu showed an increased selectivity with a strong preference for the remaining large bushes (large A. nilotica), followed by a sharp decrease in selectivity in the hot dry season when they also fed from significant numbers of medium trees. Impala had little reaction to the experimental changes in the availability of bush categories in either season. We suggest that both kudu and impala selected bushes on the basis of the potential number of bites they can provide, and this resulted in different search strategies. Kudu focussed on the larger bushes which have a larger number of twigs which are out of reach of impala and kudu also probably directed their path preferentially towards the few larger bushes to maximize encounter rates with this favoured bush category. These differences in bush selection process lead to a low overlap in resource use between the two browsers in this type of savanna.     

Damage potential of an introduced biological control agent Agonosoma trilineatum (F.) on bellyache bush (Jatropha gossypiifolia L.)

The seed-feeding jewel bug, Agonosoma trilineatum (F.), is an introduced biological control agent for bellyache bush, Jatropha gossypiifolia L. To quantify the damage potential of this agent, shadehouse experiments were conducted with individual bellyache bush plants exposed to a range of jewel bug densities (0, 6 or 24 jewel bugs/plant). The level of abortion of both immature and mature seed capsules and impacts on seed weight and seed viability were recorded in an initial short-term study. The ability of the jewel bug to survive and cause sustained damage was then investigated by measuring seed production, the survival of adults and nymph density across three 6-month cycles. The level of seed capsule abortion caused by the jewel bug was significantly affected by the maturity status of capsules and the density of insects present. Immature capsules were most susceptible and capsule abortion increased with jewel bug density. Similarly, on average, the insects reduced the viability of bellyache bush seeds by 79% and 89% at low and high densities, respectively. However, sustaining jewel bug populations for prolonged periods proved difficult. Adult survival at the end of three 6-month cycles averaged 11% and associated reductions in viable seed production ranged between 55% and 77%. These results suggest that the jewel bug has the potential to reduce the number of viable seeds entering the soil seed bank provided populations can be established and maintained at sufficiently high densities.     

Searching at different spatial scales: the foraging behaviour of the aphid parasitoid Aphidius rosae in rose bushes

The searching patterns of the aphid parasitoid Aphidius rosae were analysed at three different spatial scales: leaves, shoots and bushes. Parasitoid females searched aphid-infested leaves and shoots intensively and remained on average more than twice as long on infested than on uninfested shoots. Patch times and oviposition numbers per shoot were highly variable both between females and for different shoot visits within females. However, at the shoot and bush level low oviposition numbers were generally found. The time spent on different behavioural patterns (searching, resting, feeding, host handling) changed significantly during subsequent shoot visits of individual females but oviposition success was not influenced by this change. Parasitoids searched individual leaves and shoots mainly by walking, while moving between shoots occurred exclusively by flight. The travel time between shoots (i.e. flight time) accounted for less than 1% of the residence time in a bush. At the bush level foraging was characterized by a high ability to localize infested shoots and consequently little time was wasted in searching on uninfested shoots. The pattern of resource exploitation of individual females was consistent with the distribution of A. rosae larvae in field samples taken from individual rose bushes.     

Effects of perennial semi-arid bunchgrass spatial patterns on performance of the invasive annual cheatgrass (Bromus tectorum L.)

Plant spatial patterns critically influence community dynamics, including plant interactions, resource distribution, and community invasibility. Research suggests that resistance of western US plant communities to further invasion by the exotic annual grass Bromus tectorum may be linked to the positions of, and spacing between, perennial plants. In particular, gaps between aggregated clusters of perennial plants may facilitate B. tectorum invasion by providing safe sites for seed germination and establishment. We tested the effects of random, regular, and aggregated bunchgrass patterns, manipulated at both community (plot) and neighborhood scales, on B. tectorum biomass and spikelet production after experimental seed addition. We found strong evidence of treatment effects on both biomass and spikelets, which varied between treatments by approximately 2.5-fold. Mean biomass and spikelet counts were lowest in plots in which bunchgrasses were aggregated at both community and neighborhood scales, likely due to the increased competition. Although not statistically distinguishable from most other treatments, B. tectorum biomass and spikelet counts were highest in plots with bunchgrass patterns that were random at the community scale and aggregated at the neighborhood scale. These plots were characterized by relatively large gaps between bunchgrass clusters, suggesting that B. tectorum may exploit gaps between aggregated perennial plants. Our results support the emerging hypothesis that community resistance to B. tectorum invasion could be increased through manipulation of perennial vegetation to reduce basal gap size and connectivity.     

Composition and clumping of seeds deposited by frugivorous birds varies between forest microsites

More frequent deposition of seeds by frugivores beneath plants in fruit could impose spatial limits to the distribution of plants dispersed by animals and contribute to species coexistence. Also, differences in diet and use of microhabitats by seed dispersers could promote spatial variation in the combination of seed species deposited. We investigated patterns of seed deposition of Miconia fosteri and Miconia serrulata (Melastomataceae) by birds in the Amazon. The goal was to determine how distribution and abundance of fruiting plants, both con‐ and hetero‐specifics, affect the spatial variability in clumping and composition of multi‐specific seed deposition. We established two 9‐ha plots in undisturbed terra‐firme understory in the Ecuadorian Amazon. Seed rain was sampled with seed traps located in four microsites: below plants of the focal species, below Anthurium eminens (Araceae), and in randomly selected microsites. We examined seed deposition in these microsites in relation to habitat, fruiting neighborhood (fruit abundance, and distance to and density of plants of the target species), and crop size of M. fosteri or M. serrulata to determine if microsites differed in abundance and species composition of seeds. Seed traps below plants in fruit received more seeds than did randomly located traps. Seeds of the target species were, moreover, more commonly deposited below con‐ rather than hetero‐specific plants. Seed aggregation below fruiting plants increased in forest neighborhoods where the abundance of fruits and the combination of fruiting plant species contributed to the arrival of seeds. Microsites differed notably in the combination of seeds deposited by frugivores, and differences were less pronounced among microsites that received seeds of M. fosteri and M. serrulata than among all microsites where at least some seed species were deposited by birds. We demonstrate that two closely related, ecologically similar species possess many similarities in their patterns of seed deposition and in the factors that affect those patterns. The combination of seed species deposited below foci of dispersal depended on the fruiting plant species, and the spatial patterns of seed deposition varied with the location of the microsite and the combination of co‐dispersed species in the neighborhood. Similar species that share the same dispersers were confronted with different combinations of seeds depending on the microsite where they arrived, which could promote forest heterogeneity in the combination of plant species.     

Resource distribution and its effect on the mating system of a longhorned beetle,Perarthrus linsleyi (Coleoptera: Cerambycidae)

Summary Adults of Perarthrus linsleyi feed on flowers of creosote bush, Larrea tridentata. Mating also occurs on the flowers and foliage of this plant. This food resource is widely and evenly distributed in space, and is usually abundant. The spatial distribution of the beetles bore no relationship to the spatial distribution of flowers among creosote bushes, nor were female beetles distributed predictably with respect to flower distribution. Males moved widely over the area under study, and moved much more frequently than females. Males actively searched for females, and mounted and began copulation attempts without preliminary courtship. Males did not engage in aggressive defense of females, creosote flowers, or creosote bushes. This species exhibits a scramble competition mating system. The spatial distribution of the food resource is a primary factor in the evolution of the mating system of Perarthrus linsleyi.     

Aggregated seed dispersal by spider monkeys limits recruitment to clumped patterns in Virola calophylla

The initial spatial pattern of seed deposition influences plant population and community structure, particularly when that pattern persists through recruitment. In a vertebrate‐dispersed rain forest tree, Virola calophylla, we found that spatially aggregated seed deposition strongly influenced the spatial structure of later stages. Seed dispersion was clumped, and seed densities were highest underneath V. calophylla females and the sleeping sites of spider monkeys (Ateles paniscus), the key dispersal agent. Although these site types had the lowest per capita seed‐to‐seedling survival, they had the highest seedling/sapling densities. Conversely, seed and seedling/sapling densities were lowest, and seed survival was highest, at sites of diurnal seed dispersal by spider monkeys. Negative density‐dependent and positive distance‐dependent seed survival thinned seed clumps. Nonetheless, the clumped dispersion at sleeping and parental sites persisted to the seedling/sapling stage because differences in seed deposition were large enough to offset differences in seed survival among these site types.     

Indirect interactions between browsers and seed predators affect the seed bank dynamics of a chaparral shrub

Interactions between herbivores and seed predators may have long-term consequences for plant populations that rely on persistent seed banks for recovery after unpredictable fires. We assessed the effects of browsing by deer and seed predation by rodents, ants and birds on the densities of seeds entering the seed bank of Ceanothus cuneatus var. rigidus, a maritime chaparral shrub in coastal California. Ceanothus produced many more seeds when protected from browsers in long-term experimental exclosures than did browsed plants, but the seed densities in the soil beneath browsed and unbrowsed Ceanothus were the same at the start of an intensive one-year study. The density of seeds in the soil initially increased in both treatments following summer seed drop: while densities returned to pre-drop levels within a few weeks under browsed plants, soil seed densities remained high for 5–8 months beneath unbrowsed plants. Rodent abundance (especially deer mice) was higher near unbrowsed plants than >30 m away, and rodents removed Ceanothus seeds from dishes in the experimental plots. At least in the short term, rodent density and rates of seed removal were inversely related to the intensity of browsing. Our data have management implications for maintaining viable Ceanothus populations by regulating the intensity of browsing and the timing, intensity and frequency of fires.Electronic Supplementary Material Supplementary material is available to authorised users in the online version of this article at .     

Limits to local spatial spread in a highly invasive annual grass (Microstegium vimineum)

The potential roles of seed and microsite limitation in local spatial spread of the invasive grass Microstegium vimineum were experimentally investigated in a woodland and open lawn in central New Jersey, USA. Plots (30 × 30 cm) in three sites previously unoccupied by M. vimineum for at least 8 years (woodland interior, woodland edge, and open lawn) were sown with ~262 M. vimineum seeds in early spring 2008. Seedling emergence, density, summer growth and autumn reproduction were compared to plots in a nearby control population where natural recruitment occurred. Seedling emergence was greatest in the open lawn (54% of seeds sown) where plants showed the greatest growth and reproduction due to high light availability. Seedling emergence was lowest in the woodland interior (24%) and edge sites (9%), and growth and reproduction were greatly reduced there (relative to the control). Plots in the open lawn supported a consistently high density of M. vimineum (>1,000 plants per m²) through the growing period (April to October). The number of seeds in both cleistogamous and chasmogamous spikelets was correlated with shoot dry mass and thus, total seed production was greatest in the sunny open lawn where plants were largest, despite high density there. Across all sites, plants in plots at the highest densities produced the most seeds. Total seed production correlated with levels of light, but not soil moisture. Both seed availability and microsite limitation may reduce the probability of establishment of new M. vimineum populations into previously unoccupied sites. Intraspecific density does not negatively affect survival or reproduction. Light and soil moisture can be limiting abiotic factors in some areas, but poor, natural seed dispersal limits the distribution of this invasive species on a local scale.     

The Effects of Endophytes on Seed Production and Seed Predation of Tall Fescue and Meadow Fescue

Fungal endophytes of grasses are often included in agricultural management and in ecological studies of natural grass populations. In European agriculture and ecological studies, however, grass endophytes are largely ignored. In this study, we determined endophyte infection frequencies of 13 European cultivars and 49 wild tall fescue (Schedonorus phoenix) populations in Northern Europe. We then examined seed production and seed predation of endophyte-infected (E+) and endophyte-free (E?) tall fescue (in wild grass populations and in a field experiment) and meadow fescue (Schedonorus pratensis; in a field experiment only). Endophytes were detected in only one of the 13 cultivars. In contrast, >90% of wild tall fescue plants harbored endophytes in 45 wild populations but were absent in three inland populations in Estonia. In three wild tall fescue study sites, 17%, 22%, and 56% of the seeds were preyed upon by the cocksfoot moth. Endophyte infection did not affect seed mass of tall fescue in the field experiment. However, seed predation was lower in E+ than E? grasses in the two tall fescue populations with higher predation rates. For meadow fescue, the mean number of seeds from E+ plants was higher than E? plants, but E? and E+ seeds had equal rates of predation by the moth. Our results suggest that the effects of grass endophytes on seed production and cocksfoot moth seed predation vary considerably among grass species, and the effects may depend on herbivore pressure and other environmental conditions.     

Does endophyte symbiosis resist allelopathic effects of an invasive plant in degraded grassland?

Allelopathic effects and plant associated systemic endophytic fungi are often thought to play a role in the invasion of exotic plant species. Here, we tested the inhibitory effects of the aqueous extracts of the hemiparasitic weed Pedicularis kansuensis on seed germination and seedling growth of endophyte-free (E−) and -infected (E+) grass species, Stipa purpurea and Elymus tangutorum. The weed extracts significantly inhibited both seed germination and seedling growth of the target grass species. Extracts from the inflorescences gave greater inhibition than those from the stems or roots, while the concentration of the extract had a direct effect on the extent of inhibition. The E+ target plants were less susceptible to the extracts than their E-counterparts. Our results suggest that the allelopathic potential of P. kansuensis will lead to increased frequencies of endophyte infected plants in grass populations.     

Effect of variation in self-incompatibility on pollen limitation and inbreeding depression in Flourensia cernua (Asteraceae) scrubs of contrasting density

Background and Aims

Selection may favour a partial or complete loss of self-incompatibility (SI) if it increases the reproductive output of individuals in the presence of low mate availability. The reproductive output of individuals varying in their strength of SI may also be affected by population density via its affect on the spatial structuring and number of S-alleles in populations. Modifiers increasing levels of self-compatibility can be selected when self-compatible individuals receive reproductive compensation by, for example, increasing seed set and/or when they become associated with high fitness genotypes.

Methods

The effect of variation in the strength of SI and scrub density (low versus high) on seed set, seed germination and inbreeding depression in seed germination (δ_germ) was investigated in the partially self-incompatible species Flourensia cernua by analysing data from self-, cross- and open-pollinated florets.

Key Results

Examination of 100 plants in both high and low scrub densities revealed that 51% of plants were strongly self-incompatible and 49 % varied from being self-incompatible to self-compatible. Seed set after hand cross-pollination was higher than after open-pollination for self-incompatible, partially self-incompatible and self-compatible plants but was uniformly low for strongly self-incompatible plants. Strongly self-incompatible and self-incompatible plants exhibited lower seed set, seed germination and multiplicative female fitness (floral display × seed set × seed germination) in open-pollinated florets compared with partially self-incompatible and self-compatible plants. Scrub density also had an effect on seed set and inbreeding depression: in low-density scrubs seed set was higher after open-pollination and δ_germ was lower.

Conclusions

These data suggest that (a) plants suffered outcross pollen limitation, (b) female fitness in partially self-incompatible and self-compatible plants is enhanced by increased mate-compatibility and (c) plants in low-density scrubs received higher quality pollen via open-pollination than plants in high-density scrubs.Key words: Flourensia cernua, population density, seed set, seed germination, female fitness, partial self-incompatibility, Mapimí Biosphere Reserve