Nectar Volume Research Articles

Nectar Uptake of a Long-Proboscid Prosoeca Fly (Nemestrinidae)-Proboscis Morphology and Flower Shape.

Simple SummaryFlies with a particularly long proboscis are characteristic of flower-visiting insects in the Greater Cape Floristic Region of South Africa. We studied an endemic nemestrinid fly species in a small isolated area of semi-natural vegetation where these insects were the only flower visitors that could drink nectar from the available long-tubed flowers of one plant species. We examined the mouthpart structures that are important for nectar uptake and the length and diameter of the proboscis in comparison with the flower sizes. This local one-to-one interaction between the fly population and its nectar host flower gave the opportunity to quantify the nectar resources available for the nemestrinid flies at the study site. By comparing the offered nectar volumes before and after flower visits, the average meal size could be estimated. Assessments of the nectar levels from measured quantities and flower size allowed us to make predictions of how various proboscis lengths could reach nectar inside floral tubes.Several Prosoeca (Nemestinidae) species use a greatly elongated proboscis to drink nectar from long-tubed flowers. We studied morphological adaptations for nectar uptake of Prosoeca marinusi that were endemic to the Northern Cape of South Africa. Our study site was a small isolated area of semi-natural habitat, where the long-tubed flowers of Babiana vanzijliae (Iridaceae) were the only nectar source of P. marinusi, and these flies were the only insects with matching proboscis. On average, the proboscis measured 32.63 ± 2.93 mm in length and less than 0.5 mm in diameter. The short labella at the tip are equipped with pseudotracheae that open at the apical margin, indicating that nectar is extracted out of the floral tube with closed labella. To quantify the available nectar resources, measurements of the nectar volume were taken before the flies were active and after observed flower visits. On average, an individual fly took up approximately 1 µL of nectar per flower visit. The measured nectar quantities and the flower geometry allowed estimations of the nectar heights and predictions of necessary proboscis lengths to access nectar in a range of flower tube lengths.

Effects of the Relatedness of Neighbours on Floral Colour

The reproductive success of plants depends both on their phenotype and the local neighbourhood in which they grow. Animal-pollinated plants may benefit from increased visitation when surrounded by attractive conspecific individuals, via a “magnet effect.” Group attractiveness is thus potentially a public good that can be exploited by individuals, with selfish exploitation predicted to depend on genetic relatedness within the group. Petal colour is a potentially costly trait involved in floral signalling and advertising to pollinators. Here, we assessed whether petal colour was plastically sensitive to the relatedness of neighbours in the annual herb Moricandia moricandioides, which produces purple petals through anthocyanin pigment accumulation. We also tested whether petal colour intensity was related to nectar volume and sugar content in a context-dependent manner. Although both petal colour and petal anthocyanin concentration did not significantly vary with the neighbourhood configuration, plants growing with kin made a significantly higher investment in petal anthocyanin pigments as a result of the greater number and larger size of their flowers. Moreover the genetic relatedness of neighbours significantly modified the relationship between floral signalling and reward quantity: while focal plants growing with non-kin showed a positive relationship between petal colour and nectar production, plants growing with kin showed a positive relationship between number of flowers and nectar volume, and sugar content. The observed plastic response to group relatedness might have important effects on pollinator behaviour and visitation, with direct and indirect effects on plant reproductive success and mating patterns, at least in those plant species with patchy and genetically structured populations.

Intraspecific competition favors ant–plant protective mutualism

AbstractThe dependency of the anti‐herbivore defense on ant–plant protective mutualism often varies depending on abiotic and biotic conditions. Although intraspecific competition is a primary interaction between neighboring plants, its effects on ant–plant mutualisms have yet to be sufficiently elucidated. In order to determine the effects of intraspecific competition and competitor genotype on ant–plant mutualisms, I conducted competition and ant‐removal experiments and examined their effects on damage to the leaves of Urena lobata var. tomentosa plants. I found that larger numbers of worker ants visited the plants growing with non‐siblings than plants growing alone and that plants growing with non‐siblings had a higher shoot to root ratio and secreted greater volumes of extrafloral nectar than plants growing alone and/or with siblings. Under the presence of both sibling and non‐sibling competitors, I observed that when ants were removed from plants, those grown with conspecific neighbors were characterized by a higher percentage of damaged leaf area than plants harboring ants. The effect of ant exclusion on leaf damage was more pronounced in plants grown with non‐siblings than those grown near siblings. However, when the plants were grown alone, I detected no significant difference in percentage leaf damage between the ant‐excluded and ant‐harboring plants. The results indicate that neighboring plants can exert strong effects on ant–plant protective mutualisms, thereby highlighting the need to take into consideration plant–plant interactions in studies on these mutualistic associations.

Temporal partitioning of diurnal bird and nocturnal small mammal visitors to a winter flowering endemic succulent

Floral nectar is an important attractant and reward for visitors, and is often produced in synchrony with peak activity of pollinators. Aloe peglerae flowers in winter, and previous studies have shown that it is pollinated primarily by diurnal generalist birds, with small mammals making additional contributions to pollination at night. Nectar produced during the day is the main attractant and reward for birds, but the nectar rewards available to small mammals are unknown. This paper investigates nectar availability in Aloe peglerae, because small mammals may be feeding on remaining, or freshly produced, nectar at night. Nectar availability over a 24-hour period was measured in screened and unscreened plants (n = ten plants per treatment), and the associated partitioning of visits by diurnal birds and nocturnal small mammals assessed. Nectar is constantly available over 24-hours, but in different quantities. Nectar volume of screened (nectar availability) and unscreened (standing crop) plants, is significantly higher early in the morning after sunrise, compared with all other sampling periods during the 24-hour period. Nectar concentration did not vary over 24-hours, averaging 11.5 ± 0.4% w/w (unscreened) across the entire 24-hour period. Peaks in visits by different guilds occurred at periods (i.e. diurnal birds and nocturnal small mammals) when nectar availability was high. Aloe peglerae has higher daytime nectar production, when its primary pollinators are most active, but the continual, albeit reduced, nectar availability at night attracts small mammals. Mobile diurnal birds, and less-mobile nocturnal small mammals, both rely on this nectar resource during dry and cold South African winters and, in turn, are important pollinators for this Critically Endangered Aloe species.

Soil Humus, Iron, Sulphate and Magnesium Content Affect Nectar Traits of Wild Garlic (Allium ursinum L.).

Recent studies revealed that from various ecological factors influencing nectar yield and quality of a plant, soil properties can be as important as microclimatic features. To date, few studies have investigated the relationship of soil characters to nectar traits of bee pollinated plants growing in natural associations. Our study intended to reveal which soil properties had the most powerful impact on nectar variables of wild garlic (Allium ursinum L.). Specimens were collected from fourteen habitats in two different years, and were potted in their original soil under the same climatic conditions. Nectar volumes and sugar concentrations were measured and soil samples were analysed for fourteen parameters. Statistical analyses revealed that the number of nectar producing Allium flowers, as well as the nectar volume and sugar content of nectar in individual flowers were influenced by both year and habitat. The humus, iron and sulphate content of soil showed negative correlation with the number of flowers producing nectar; total nectar volumes were negatively correlated with humus and iron content, but positively affected by magnesium content of the soil. Our results suggest that in addition to the effect of microclimatic factors, certain soil properties can have significant impact on nectar traits.

Investigating pollination strategies in disturbed habitats: the case of the narrow-endemic toadflax Linaria tonzigii (Plantaginaceae) on mountain screes

Plant mating systems may reflect an adaptation to a habitat type, with self-pollination being potentially common in unstable and disturbed conditions. We investigated the reproductive ecology of an Alpine, narrow-range toadflax, Linaria tonzigii Lona (Plantaginaceae), occurring in steep and dynamic mountain screes. We explored self-compatibility and spontaneous autogamy, seed viability, daily nectar production, pollinator behaviour and pollen transfer in wild populations, using hand pollination treatments, quantification of nectar volume, viability Tetrazolium assay, active pollinator sampling and video recordings, and UV-bright dust for pollen substitution. After ex novo sequencing of several genetic regions of L. tonzigii, we performed a multi-marker phylogenetic analysis of 140 Linaria species and tracked the occurrence of the self-compatibility trait. Our results showed that this species is self-compatible, pollinated mostly via spontaneous autogamy and pollinator-mediated geitonogamy, and self-pollinated seeds are as viable as cross-pollinated ones. Selfing could be due to pollinator rarity because, despite the studied species providing a high nectar volume, wild bees, moths and small beetles infrequently visited its flowers in the sparsely vegetated scree slopes. In addition, a preliminary survey showed a low genetic haplotype diversity in the study plant. Moreover, the phylogeny shows that self-compatibility is scattered in the tree, suggesting the adaptive nature of this reproductive trait in the genus Linaria. This study supports for theories that high prevalence of selfing is an adaptation to environments unfavourable for cross-pollination, and particularly where pollinators are rare, such as in perturbed, poorly vegetated high-elevation habitats.

Analysis on floral nectar characteristics among the selected black locust (Robinia spp.) individuals

This study aimed to determine the value of honey source on Robinia by analyzing flower morphology and nectar characteristics in floral nectar of eight selected individuals. The mean nectar volume secreted by genus Robinia was 1.7 ± 1.0 µL. Among the samples, PR (R. margaretta) and HR (R. pseudoacacia) secreted the highest and lowest nectar volumes—3.0 ± 1.1 and 1.1 ± 0.7 µL, respectively. The mean sugar concentration was 44.8 ± 6.1% (range, 40.1–51.4%). The ANOVA results revealed a statistically significant difference in nectar volume and sugar concentration among the eight individuals (p < 0.05). The free sugar content ranged from 0.39 (HR) to 0.78 (KR) mg/μL, and nectar sugar contents ranged from 0.31 (HR) to 1.53 (PR) mg per flower. The sucrose/hexose ratio ranged from 0.5 to 3.6, and sucrose was high in all samples. The results of the Kruskal-Wallis H test revealed significant differences in free sugar content (mg/µL), nectar sugar content per flower and sucrose/hexose ratio (p < 0.05). There were close correlations between nectar characteristics and flower morphology as followed; 1) nectar volume and nectar sugar content per flower (r = 0.976), 2) nectar volume and calyx length (r = 0.952), 3) sugar concentration in nectar and length of inflorescence (r = 0.952). Asparagine was the most abundant (average; 60.2%) amino acid, followed in decreasing order by alanine (6.9%), glutamine (5.2%), and serine (4.7%). The results of Kruskal-Wallis H tests showed that the rate of amino acids of alanine, glutamine, glutamic acid, and arginine significantly differed among the samples (p < 0.05).

Floral biology of Salvia stachydifolia, a species visited by bees and birds: connecting sexual phases, nectar dynamics and breeding system to visitors’ behaviour

Abstract Aims Adaptive convergence in floral phenotype among plants sharing a pollinator guild has been acknowledged in the concept of pollination syndrome. However, many plants display traits associated with a given syndrome, but are visited by multiple pollinators. This situation may indicate the beginning of a pollinator shift or may result in a stable situation with adaptations to different pollinators. In Salvia stachydifolia, a previous study suggested that flower shape is optimized to maximize the contribution to pollination of bees and hummingbirds. Here, we studied three additional aspects of its floral biology: sexual phases, nectar dynamics and breeding system, and examined their connection with pollinators’ behaviour to explore the presence of adaptations to bee and/or hummingbird pollination. Methods Using a greenhouse population, we applied five pollination treatments to characterize breeding system. To determine sexual phases, we recorded flower opening, anther dehiscence, corolla fall and stigma receptivity. Additionally, we characterized nectar volume and concentration dynamics along the day. Finally, to determine pollinator assemblage and visitation patterns, we performed field observations and recorded pollinators’ behaviour. Important Findings Salvia stachydifolia was partially protandrous and self-compatible, but open-pollinated plants attained the highest reproductive success, suggesting that reproduction is mainly dependent on pollinator activity. Bombus opifex bumblebees were the most frequent visitors, but Sappho sparganura hummingbirds dominated visits early in the morning and at dusk. Nectar was typical of bumblebee pollination. We suggest that the bee–hummingbird mixed visitation constitutes an unstable evolutionary situation, making S. stachydifolia an ideal system to understand the ecological circumstances in which pollination shifts occur.

Altitude‐related shift of relative abundance from insect to sunbird pollination in Elaeagnus umbellata (Elaeagnaceae)

AbstractThe evolution of floral traits has been thought to be influenced by local, effective pollinators. However, little attention has been paid to the possibility that altitudinal variation in floral traits could be mediated by local pollinator functional groups, particularly a shift from bees to birds. Plant size, floral traits, pollinators and their pollination roles were investigated in the spring‐flowering shrub Elaeagnus umbellata (Elaeagnaceae) at three altitudes (1160, 1676, and 2050 m) in Minshan, Sichuan Province, on the northern rim of the Hengduan Mountains, southwest China. Compared to lower altitudes, higher‐altitude plants were smaller but the floral tubes were longer, with a larger volume of nectar of lower sugar concentration but with a greater proportion of sucrose. The visitation frequency of bees decreased with altitude, whereas the sunbirds did the opposite. Birds and bees foraged for nectar but not pollen, and birds deposited more pollen grains per visit relative to bees and least were syrphid flies. Excluding birds decreased seed set at high but not at mid‐ or low altitude. Our study of E. umbellata revealed an association between altitudinal variation in floral traits and a change in the relative abundance of the major pollinators with altitude from majority bees to majority sunbirds. Although abiotic factors also tend to vary with altitude and can affect floral traits, nectar properties of “pro‐bird” pollination were observed at high altitude.

Exploitative competition and displacement mediated by eusocial bees: experimental evidence in a wild pollinator community

Eusocial bees are likely to be ecologically important competitors for floral resources, although competitive effects can be difficult to quantify in wild pollinator communities. To investigate this, we excluded honeybees (HBE treatment), bumblebees (BBE) or both (HB&BBE) from wild-growing patches of bramble, Rubus fruticosus L. agg., flowers in two eight-day field trials at separate locations, with complementary mapping of per-site local floral resource availability. Exclusions increased per-flower volume of nectar and visitation rates of non-excluded bees, compared to control patches with no bee exclusions (CON). There was a large increase in average nectar standing crop volume both at Site 1 (+ 172%) and Site 2 (+ 137%) in HB&BBE patch flowers, and no significant change in HBE or BBE, compared to CON patches. Foraging bee responses to exclusion treatments were more pronounced at Site 2, which may be due to lower local floral resource availability, since this is likely to increase the degree of exploitative competition present. Notably, at Site 2, there was a 447% increase in larger-bodied solitary (non-Apis/Bombus) bees visiting HB&BBE patches, suggesting ecological release from competition. Hoverflies showed no response to bee removals. Numbers of other non-bee insect groups were very small and also showed no clear response to exclusions. Our findings reveal patterns of competitive exclusion between pollinator groups, mediated by resource depletion by eusocial bees. Possible long-term implications of displacement from preferred flowers, particularly where alternative forage is reduced, are discussed.Significance statementUnderstanding patterns of exploitative competition and displacement is necessary for pollinator conservation, particularly for vulnerable or threatened species. In this research, experimental methods reveal underlying patterns of resource competition exerted by eusocial bees in a wild pollinator community. We show that honeybees and bumblebees competitively displace each other and particularly solitary (non-Apis/Bombus) bees from bramble, an important native nectar and pollen source. Effects were stronger where local floral resource availability was identified to be limited. Notably, following experimental exclusion of both honey- and bumblebees from flowers, visitation by solitary bees increased by up to 447%, strongly suggesting ecological release from competition. These results highlight the need for informed landscape management for pollinator wellbeing, including appropriate honeybee stocking densities and improved floral resource availability.

The role of alanine synthesis and nitrate-induced nitric oxide production during hypoxia stress in Cucurbita pepo nectaries.

Floral nectar is a sugary solution produced by nectaries to attract and reward pollinators. Nectar metabolites, such as sugars, are synthesized within the nectary during secretion from both pre-stored and direct phloem-derived precursors. In addition to sugars, nectars contain nitrogenous compounds such as amino acids; however, little is known about the role(s) of nitrogen (N) compounds in nectary function. In this study, we investigated N metabolism in Cucurbita pepo (squash) floral nectaries in order to understand how various N-containing compounds are produced and determine the role of N metabolism in nectar secretion. The expression and activity of key enzymes involved in primary N assimilation, including nitrate reductase (NR) and alanine aminotransferase (AlaAT), were induced during secretion in C. pepo nectaries. Alanine (Ala) accumulated to about 35% of total amino acids in nectaries and nectar during peak secretion; however, alteration of vascular nitrate supply had no impact on Ala accumulation during secretion, suggesting that nectar(y) amino acids are produced by precursors other than nitrate. In addition, nitric oxide (NO) is produced from nitrate and nitrite, at least partially by NR, in nectaries and nectar. Hypoxia-related processes are induced in nectaries during secretion, including lactic acid and ethanolic fermentation. Finally, treatments that alter nitrate supply affect levels of hypoxic metabolites, nectar volume and nectar sugar composition. The induction of N metabolism in C. pepo nectaries thus plays an important role in the synthesis and secretion of nectar sugar.

Cordia subcordata (Boraginaceae), a distylous species on oceanic coral islands, is self-compatible and pollinated by a passerine bird

Background and aims – Distyly is usually rare on oceanic islands, which is probably due to the difficulty for distylous plants to colonize those islands. However, Cordia subcordata was observed to be distylous with short- and long-styled morphs on the Xisha Islands in the South China Sea. To characterize the reproduction system of Cordia subcordata and to understand how this distylous species maintains itself on these islands, we studied its reproductive and pollination biology.Methods – Seed set and pollen tube growth under manipulated intermorph, intramorph, and self-pollination were examined to investigate self-incompatibility in the species. The number of pollen grains deposited on the stigmas after a single pollinator visit were counted to investigate the pollination efficiency of different visitors. Key results – Our study indicated that Cordia subcordata shows reciprocal herkogamy as is typical in distylous species. Pollen tubes could reach the base of the style and move into the ovules under all the manipulated pollination treatments in both morphs. Seed set resulting from four hand-pollination experiments did not show any differences between both morphs, suggesting that Cordia subcordata lacks heterostylous self-incompatibility. The most frequent flower visitors, Zosterops japonicus and Apis cerana, were observed foraging on the large volumes of nectar and pollen grains, respectively, with Zosterops japonicus being the most effective pollinator, depositing large number of pollen grains on the stigmas during their visits.Conclusions – Our findings show that Cordia subcordata established itself and persists in the archipelago by producing fruits through a combination of self-compatibility and pollination by the most common passerine bird on the oceanic islands.

Light availability influences the intensity of nectar robbery and its effects on reproduction in a tropical shrub via multiple pathways.

The multiple exogenous pathways by which light availability affects plant reproduction (e.g., via influence on attraction of mutualists and antagonists) remain surprisingly understudied. The light environment experienced by a parent can also have transgenerational effects on offspring via these same pathways. We evaluated (a) the influence of light availability on floral traits in Odontonema cuspidatum, (b) the relative importance of the pathways by which light influences nectar robbery and reproductive output, and (c) the role of parental light environment in mediating these relationships. We conducted a reciprocal translocation experiment using clonally propagated ramets and field surveys of naturally occurring plants. Light availability influenced multiple floral traits, including flower number and nectar volume, which in turn influenced nectar robbery. But nectar robbery was also directly influenced by light availability, due to light effects on nectar robber foraging behavior or neighborhood floral context. Parental light environment mediated the link between light availability and nectar robber attraction, suggesting local adaptation to low-light environments in floral visitor attraction. However, we found no transgenerational effect on reproduction. Our findings demonstrate that exogenous pathways by which light influences plants (particularly through effects on floral antagonists) can complicate the positive relationship between light availability and plant reproduction. Our results are among the first to document effects of light on floral antagonists and clonal transgenerational effects on flower visitor attraction traits.

How do insects choose flowers? A review of multi‐attribute flower choice and decoy effects in flower‐visiting insects

Understanding why animals (including humans) choose one thing over another is one of the key questions underlying the fields of behavioural ecology, behavioural economics and psychology. Most traditional studies of food choice in animals focus on simple, single-attribute decision tasks. However, animals in the wild are often faced with multi-attribute choice tasks where options in the choice set vary across multiple dimensions. Multi-attribute decision-making is particularly relevant for flower-visiting insects faced with deciding between flowers that may differ in reward attributes such as sugar concentration, nectar volume and pollen composition as well as non-rewarding attributes such as colour, symmetry and odour. How do flower-visiting insects deal with complex multi-attribute decision tasks? Here we review and synthesise research on the decision strategies used by flower-visiting insects when making multi-attribute decisions. In particular, we review how different types of foraging frameworks (classic optimal foraging theory, nutritional ecology, heuristics) conceptualise multi-attribute choice and we discuss how phenomena such as innate preferences, flower constancy and context dependence influence our understanding of flower choice. We find that multi-attribute decision-making is a complex process that can be influenced by innate preferences, flower constancy, the composition of the choice set and economic reward value. We argue that to understand and predict flower choice in flower-visiting insects, we need to move beyond simplified choice sets towards a view of multi-attribute choice which integrates the role of non-rewarding attributes and which includes flower constancy, innate preferences and context dependence. We further caution that behavioural experiments need to consider the possibility of context dependence in the design and interpretation of preference experiments. We conclude with a discussion of outstanding questions for future research. We also present a conceptual framework that incorporates the multiple dimensions of choice behaviour.

Foraging Behavior of Apis mellifera Linn. Visiting Some Plant Flowers in Aljabal Alakhder Region –Libya

The study aimed to investigate the effects of nectar secretion and climate conditions on the number of honeybee workers foraging on flowers of three different plant species. Nectar samples were taken at different hours of the day. Handling and traveling time of each bee per flower were recorded. The results showed a significant difference during daylight hours on nectar volume (P&gt;0.05). The highest amount of nectar was recorded at 10 am on a Prunus domestica flower plant (0.5± 0.2) and the lowest on a Pyrus communis flower plant at 8:00 am with (0.0132 ± 0.008). Also, the highest recorded handling time was on a Malus domestica flower plant at 10 am with (6.1± 1.7 Sec). And while there was an absence of mean handling time at 4:00 pm on the P. communis flower plant, The results showed that the highest traveling time recorded was on a M. domestica flower plant at 12 am with (2.2 ± 0.1 Sec) compared with the P. communis flower plant that recorded the lowest traveling time at 4:00 pm with (0.1± 0.1 Sec). Furthermore, the results revealed that the preference of Apis mellifera was the M. domestica flower plant. The findings showed a significance (P&gt;0.05) between the effects of climate conditions on the number of bees during visits, while also revealing that there was a relationship between high temperatures and an increase in the number of visiting bees. Meanwhile, the number of visits decreased during the hours of observation with lower humidity.

Salvage of floral resources through re-absorption before flower abscission

Plants invest floral resources, including nectar and pigment, with likely consequent reproductive costs. We hypothesized that plants, whose flowers abscise with age, reabsorb nectar and pigment before abscission. This was tested with flowers of Rhododendron decorum, which has large, conspicuous white flowers that increasingly abscise corollas as flowers age. As this species is pollinated by bees, we also hypothesized that nectar concentration would be relatively high (i.e., > 30% wt/vol) and petals would contain UV-absorbing pigment. Floral nectar volume and concentration were sampled on successive days until abscission (up to ten days old, peak at five days) and for sub-sample of four-day-old flowers. Flowers just abscised were similarly sampled. Flower colours were measured using a modified camera, with recordings of spectral reflectance for abscised and open non-abscised flowers. Pigment content was summed values of red, green, blue channels of false color photos. As expected, flowers reabsorbed almost all nectar before abscission, separately reabsorbing nectar-sugar and nectar-water, and petals contained UV-absorbing pigment. However, flowers did not reabsorb pigment and nectar-concentration was < 30% wt/vol. That flowers reabsorb nectar, not pigment, remains unexplained, though possibly pigment reabsorption is uneconomical. Understanding floral resource reabsorption therefore requires determination of biochemical mechanisms, plus costs/benefits for individual plants.

Bees provide pollination service to Campsis radicans (Bignoniaceae), a primarily ornithophilous trumpet flowering vine

Pollination syndromes refer to stereotyped floral characteristics (flower colour, shape, etc.) that are associated with a functional group of pollinators (bee, bird, etc.). The trumpet creeper Campsis radicans, endemic to the southeast and mid‐west United States, has been assigned to the hummingbird‐pollination syndrome, due mainly to its red, trumpet‐shaped flowers. Previous studies demonstrated that the ruby‐throated hummingbird Archilochus colubris is C. radicans' primary pollinator, but anecdotal data suggest various bee species may provide pollination service when hummingbirds are absent. This study characterised C. radicans nectar volume and concentration by time of day. Nectar volume was suitable for hummingbirds, but concentration was higher than typical hummingbird‐pollinated plants (∼20% w/w); at ∼30% w/w, it approached the concentration expected in bee‐pollinated plants (∼50% w/w). We also found substantial amounts of nectar at night. Two C. radicans populations received virtually no hummingbird visits, but the number of bees were markedly higher than in the populations previously described. Interestingly, there were no night‐time visitors despite the large quantity of nocturnal nectar. Based on previously published pollen delivery per visit by various species, this study estimated that cumulative deposition by bees routinely reached pollen deposition thresholds for setting fruit in C. radicans. They are, unequivocally, the predominant pollinators in these populations, thus providing pollination service in the absence of hummingbirds. These results highlight C. radicans as a food source for native bees and add to the understanding of how floral phenotypes can facilitate pollination by disparate functional groups.

Effects of Age and Layers of Trees and Temperature on Nectar Volume and Concentration of Croton Macrostachyus Hochst. ex Delile

Croton macrostachyus Hochst.ex Delile is a species of the genus Croton, Euphorbiaceae family, commonly known as the spurge family and it is known as major honeybee forages having more nectar and the study was carried out to evaluate effects of its layers, and age and temperature on its nectar volume and concentration. Nectar is a floral resource commonly sought after by plant visitors, because of its nutritional importance. Effects of temperature, layers of trees and plants age on nectar volume and concentration of youngest, medium and oldest age of croton was measured. Results indicated that nectar concentrations and volume of youngest age were no more affected by temperature like that of medium and oldest age. Temperature and age has significant effect on volume (p = 0.0001) and their interactions is also significant (p = 0.012).Temperature has significant effects on nectar concentration (p = 0.000). Oldest plants had highest concentration of 10.1 w/w morning and afternoon 36.5 w/w at 4:00 PM for whereas medium plants had nectar concentration of 5.7 w/w morning and afternoon 16.7 w/w and the smallest had nectar concentration of 2.7 w/w morning and afternoon 9.1 w/w. I conclude that future temperature rise could have negative effect on nectar secreation for honey productions since for croton also no nectar secreation was observed after peak temperature of its nectar secreation that was 30°C. Studying factors affecting nectar volume and concentrations is important to increase productions and the productivity of honey to generate income and for medicinal value of honey. Keywords : Age of trees ,Croton macrostachyus , nectar concentration, nectar volume, temperature, trees layers DOI: 10.7176/JNSR/11-18-01 Publication date: September 30 th 2020

Contrasting effects of herbivore damage type on extrafloral nectar production and ant attendance

The ant-plant mutualism mediated by extrafloral nectaries (EFNs) is based on the provision of extrafloral nectar (a sugar-rich liquid) in exchange for ant defense against herbivores. The extrafloral nectar production can vary depending on the intensity or types of leaf damage caused by different mouthparts of insect herbivores (i.e., sucking or chewing insects). However, it is poorly known how the type of herbivore damage changes the outcomes of tri-trophic interactions. Here, we address how the damage inflicted by different herbivore groups affects extrafloral nectar production and ants’ attendance and aggressiveness. Through an experimental field study, we tested whether the type of leaf damage, sucking or chewing, changes extrafloral nectar volume and sugar concentration, and subsequently ant composition and behavior. We evaluated the extrafloral nectar production and ant attendance and aggressiveness before and after simulated herbivory in Qualea parviflora (Vochysiaceae), a Brazilian savanna EFN-bearing plant. We found that only plants with sucking damage increased the sugar concentration of their extrafloral nectar, only plants with chewing damage increased ant abundance, and surrogate herbivore predation differed before and after simulated herbivory only for sucking damage. We provided the first evidence that the type of damage can influence ant aggressiveness via changes in extrafloral nectar production, translating to changes in the outcomes of this ant-plant mutualism. Ultimately, studies should consider the effects of herbivore damage type when studying insect-plant interactions.

Plant protection services mediated by extrafloral nectaries decline with aridity but are not influenced by chronic anthropogenic disturbance in Brazilian Caatinga

Abstract Most terrestrial species occur in human‐modified landscapes that are experiencing climate change. In addition to direct impacts on species, both anthropogenic disturbance and climate change can have important effects through changes in species interactions, including the disruption of ecological services provided by them. Here we investigate how chronic anthropogenic disturbance (CAD) and aridity affect the effectiveness of plant protection services provided by ants to plants bearing extrafloral nectaries (EFNs). The study was conducted across 13 01‐ha plots distributed along CAD and aridity gradients in Caatinga vegetation of northeastern Brazil. We focused on Pityrocarpa moniliformis, the most abundant and widely distributed EFN‐bearing tree species occurring in our study area, and we used experimental attack rates on termites as a measure of effectiveness of ant protection services. We investigated the relative roles of nectar production (volume and concentration) and ant species composition in mediating the effects of CAD and aridity on the effectiveness of protection services. Attack rates by ants declined with increasing aridity but were not related to CAD. The volume of extrafloral nectar declined with increasing CAD but was not affected by aridity, whereas the concentration was not related to either CAD or aridity. The composition of attendant ant species varied with aridity but not with CAD. Synthesis. Our findings suggest that CAD does not affect plant‐protection services mediated by EFNs in Brazilian Caatinga. However, ant‐protection services declined with increased aridity, and this occurred through changes in the composition of attendant ant species rather than by changes in the production of extrafloral nectar. Such a response to increasing aridity highlights the vulnerability of EFN‐bearing plants to climate change through decreased predation of herbivores.