Did insect pollination cause increased seed plant diversity?

The dominant paradigm for the disproportionate number of flowering plants is the unique coevolution that they underwent with pollinating insects. The theory underlying this biotic pollination hypothesis contradicts more generally accepted evolutionary theory. Furthermore, various lines of empirical evidence falsify the biotic pollination hypothesis: (a) several lineages of plants were insect pollinated – angiosperms, Gnetales, Bennettitales, Cheiro-lepidiaceae, Medullosales, and Cycadales - yet only the first four were ever diverse or underwent radiations; (b) the predicted rise in insect diversity, which was coupled with angiosperm radiation, does not appear in the fossil record; (c) the family Poaceae (grasses) are wind pollinated, yet are exceptionally diverse and species-rich; and (d) the family Formicidae (ants) were not pollinators, yet are exceptionally species-rich and ecologically dominant. I enumerate many alternate (and seldom investigated) hypotheses for these patterns of seed plant diversity, keeping in mind that although I show that insect pollination was neither a necessary nor sufficient condition for large numbers of species, it may have played a substantial role in both plant and insect speciation. Alternatively, existing theory regarding the biotic pollination hypothesis can be refined in an attempt to eliminate the aforementioned empirical anomalies and theoretical inconsistencies.     

Angiosperm growth habit,dispersal and diversification reconsidered

Summary Previous studies have sought to elucidate the relationship between dispersal mode (biotic versus abiotic) and the taxonomic diversification of angiosperm families, but with ambiguous results. In this study, we propose the hypothesis that the combination of (1) the large seed size required of plants germinating in closed, light-poor environments and (2) the necessity to move disseminules away from the maternal plant in order to avoid intraspecific competition, predation and pathogens should favour biotically-dispersed relative to abiotically-dispersed woody arborescent angiosperms, resulting in higher diversification of the former. In this paper, we seek patterns of diversification that support this hypothesis. We examine the association between dispersal mode, growth habit and taxonomic richness of monocotyledon and dicotyledon families using (1) contingency table analyses to detect the effect of dispersal mode on the relative abundances and diversification of woody versus herbaceous taxa and (2) non-parametric analyses of variance to detect the statistical effect of dispersal mode on taxonomic diversification (mean number of species per genus, genera per family and species per family) in monocot and dicot families dominated by biotic or abiotic dispersal. We found a clear statistical effect of dispersal mode on diversification. Among families of woody dicots, dispersal by vertebrates is associated with significantly higher levels of species per genus, genera per family and species per family than is abiotic dispersal. The same pattern is observed among woody monocots, but is not significant at the 0.05 level. Among families of herbaceous monocots and dicots, the situation is reversed, with abiotically-dispersed families exhibiting higher levels of diversification than vertebrate-dispersed families. When woody and herbaceous families are pooled, there is no association between dispersal mode and diversification. These data coincide with evidence from the fossil record to suggest vertebrate dispersal has positively contributed to the diversification of woody angiosperms. We suggest that vertebrate dispersal may have promoted the diversity of extant taxa by reducing the probability of extinction over evolutionary time, rather than by elevating speciation rates. Our results suggest vertebrate dispersal has contributed to, but does not explainin toto, the diversity of living angiosperms.     

Reproductive ecology and pollen representation among neotropical trees

Three years of pollen trapping data from Barro Colorado Island, Panama, are compared with local vegetation inventories. Two hypotheses relating pollen representation to ‘messy’ pollination and flower form are tested. Dioecious taxa were found to be over‐represented in pollen spectra compared with their occurrence in local forests. Similarly, anemophilous and ‘messy’ pollination types were found to be over‐represented. While anemophilous taxa were the best dispersed pollen types, zoophilous taxa were also well‐represented in dispersal classes of 20–40 m and > 40 m. Thus pollen arriving to lake sediments is most likely to be from anemophilous species or those zoophilous species exhibiting ‘messy’ pollination syndromes. Pollination mechanisms will predictably bias the fossil record against certain flower morphologies. These data are of significance to those using the fossil pollen record to reconstruct the timing and sequence of angiosperm evolution. These data help prioritize plants to be included in modern pollen reference collections and to focus the search for ‘unknown’ types on most‐likely candidate families.     

Speciation in Hawaiian angiosperm lineages: cause, consequence, and mode

The biota of Hawaiian Islands is derived entirely from long distance dispersal, often followed by in situ speciation. Species descended from each colonist constitute monophyletic lineages that have diverged to varying degrees under similar spatial and temporal constraints. We partitioned the Hawaiian angiosperm flora into lineages and assessed morphological, ecological, and biogeographic characteristics to examine their relationships to variation in species number (S). Lineages with external bird dispersal (through adhesion) were significantly more species-rich than those with abiotic dispersal, but only weakly more species-rich than lineages with internal bird dispersal (involving fleshy fruits). Pollination mode and growth form (woody vs. herbaceous) had no significant effect on S, in contrast to studies of angiosperm families. S relates positively to the geographic and ecological range size of whole lineages, but negatively to local abundance and mean range sizes of constituent species. Species-rich lineages represent a large proportion of major adaptive shifts, although this appears to be an artifact of having more species. Examination of 52 sister species pairs in numerous lineages provides evidence for allopatric (including peripheral isolates) and parapatric (ecological) modes, with 15 cases of each. Although postspeciational dispersal may obscure these modes in many of the remaining cases, instances of sympatric and hybrid speciation are also discussed. Because speciation is both a consequence and a cause of ecological and biogeographic traits, speciation mode may be integral to relationships between traits. We discuss the role of speciation in shaping the regional species pool.     

Responses of pre‐dispersal seed predators to sequential flowering of Dipterocarps in Malaysia

Many species of Dipterocarpaceae and other plant families reproduce synchronously at irregular, multi‐year intervals in Southeast Asian forests. These community‐wide general flowering events are thought to facilitate seed survival through satiation of generalist seed predators. During a general flowering event, closely related Shorea species (Dipterocarpaceae) stagger their flowering times by several weeks, which may minimize cross pollination and interspecific competition for pollinators. Generalist, pre‐dispersal seed predators might also track flowering hosts and influence predator satiation. We addressed the question of whether pre‐dispersal seed predation differed between early and late flowering Shorea species by monitoring flowering, fruiting and seed predation intensity over two general flowering events at the Pasoh Research Forest, Malaysia. Pre‐dispersal insect seed predators killed up to 63 percent of developing seeds, with Nanophyes shoreae, a weevil that feeds on immature seeds being the most important predator for all Shorea species. This weevil caused significantly greater pre‐dispersal seed predation in earlier flowering species. Long larval development time precluded oviposition by adults that emerged from the earliest flowering Shorea on the final flowering Shorea. In contrast, larvae of weevils that feed on mature seeds before seed dispersal (Alcidodes spp.), appeared in seeds of all Shorea species almost simultaneously. We conclude that general flowering events have the potential to satiate post‐dispersal seed predators and pre‐dispersal seed predators of mature fruit, but are less effective at satiating pre‐dispersal predators of immature fruit attacking early flowering species.     

Water links the historical and contemporary components of the Australian bird diversity gradient

Aim To document the geographical structure of the historical signal in the continental species richness gradient of birds and evaluate the influences of contemporary and historical climatic conditions on the generation and maintenance of the richness pattern. Location Australia. Methods We used range maps of breeding birds to generate the spatial pattern of species richness at four grain sizes, and two molecular phylogenies to measure the level of evolutionary development of avifaunas at each grain size. We then used simple correlation and path analysis to generate a statistical model of species richness using environmental predictor variables and compared the spatial patterns of richness and mean evolutionary development to identify possible environmental links between richness and net diversification rates across the continent. Results The contemporary richness pattern is well explained statistically by actual evapotranspiration (a measure of water–energy balance), operating both directly and indirectly through plant production, and this is robust to the spatial resolution of the analysis. Further, species richness and the mean level of evolutionary development of faunas show a strong spatial correspondence, such that dry areas support both fewer species and species from more highly derived families, whereas wet areas support more species of both basal and derived families. The evolutionary pattern conforms to a similar pattern known for plants and is probably explained by the increase in aridity in western and central Australia arising in the Miocene. Main conclusion The contemporary bird richness gradient contains a historical signal and reflects the effects of both current levels of water availability as well as changes in rainfall patterns extending over evolutionary time. The historical signal persists even in the absence of obvious hard barriers to dispersal.     

Accessory costs of seed production

Accessory costs of reproduction are those that are necessary to mature a seed, but that do not involve the direct cost of provisioning the seed itself. This study aims to quantify accessory costs in a range of species, and test whether they decrease as a proportion of total reproductive expenditure with increasing seed mass, as might be expected if economies of scale came into play at larger seed sizes. We also test whether accessory costs varied with growth form, pollination mode, and dispersal mode, with the expectation that biotic pollination and dispersal modes should incur greater costs. Reproductive allocation (dry biomass) over one season, was calculated for 14 diclinous angiosperm species. Accessory costs averaged 73% of total reproductive allocation, with the majority spent on packaging and dispersal. Total accessory costs, packaging and dispersal costs, and costs incurred prior to pollination were proportional to direct costs of reproduction in major axis regressions. However, larger seeded species incurred significantly greater costs associated with aborted seeds and fruits, and matured a smaller proportion of ovules. This is consistent with larger seeded species being more selective of the ovules/embryos matured than small-seeded species. Total accessory costs, and proportion of ovules aborted, were also significantly greater for biotically dispersed species, but only due to an association with larger seed masses. Costs associated with abortions were lower for biotically pollinated species, due to a general trend of more ovules per ovary, resulting in greater cost sharing. This study demonstrates that expenditure on items other than seeds accounts for the majority of reproductive allocation in flowering plants. Yet, far more literature exists on seed mass variation than on investment in accessory structures. We found a proportional relationship between accessory costs and seed mass that warrants further investigation within the context of selection on margin returns on investment.     

Testing the impact of climate variability on European plant diversity: 320,000 years of water-energy dynamics and its long-term influence on plant taxonomic richness

Models examining the present-day relationship between macro-scale patterns in terrestrial species richness and variables of water and energy demonstrate that a combined water–energy model is a good predictor of richness in mid-to-high latitude regions. However, the power of the individual water and energy variables to explain this richness through time has never been explored. Here, we assess how well energy and water can predict long-term variations in plant richness using a 320 000-year fossil pollen data set from Hungary. Results demonstrate that a combined water–energy model best explains the variation in plant diversity through time. However, this long temporal record also demonstrates that amplitude of energy variation appears to be a strong determinant of richness. Decreased richness correlates with increased climate variability and certain species appear to be more susceptible according to their ecological traits. These findings have important implications for predicting richness at times of increasing climate variability.     

Species diversity and ecological range in relation to ploidy level in the flora of the Pyrenees

Polyploidy is a major process in plant evolution. Surprisingly, no study has examined its role in species diversification and ecological distribution in relation to other life history traits. In this study, we examine to what extent polyploidy and the other traditionally examined biological traits (pollination mode, dispersal mode and growth form) account for ecological and taxonomic diversity in the flora of the Pyrenees. Fifty genera (in 22 angiosperm families) were classified according to ploidy level, growth form, pollination mode and dispersal mode, and 451 species and/or subspecies in these 50 genera were classified according to ploidy level and growth form. We examined the contribution of ploidy level, pollination and dispersal modes and growth form to (i) the ecological range of species and genera, i.e., the number of natural habitats (defined by a combination of ecological characteristics) where they occur, and (ii) the taxonomic diversity of the 50 genera. Ploidy level and dispersal mode had significant effects on the taxonomic diversity of the 50 genera. Taxonomic diversity, but not polyploidy per se, was significantly correlated with ecological range of genera. For individual species, diploids had a larger ecological range than polyploids, and herbaceous growth forms had wider ecological distributions than other growth forms. Our results indicate that polyploidisation may be a source of ecological diversification of genera, not by increasing the ecological range of particular polyploid species compared to diploids, but rather by creating taxonomic diversity that leads in some genera to a diversification of the habitats occupied by different ploidy levels. This observation is consistent with previous observations of ecological divergence of chromosomal races in some species in the Alps and in the Pyrenees. As found in other studies, species diversification in the studied flora appears to be greatly influenced by the occurrence of multiple dispersal modes, while ecological range of species or subspecies is significantly increased by the presence of herbaceous species.     

Historical biogeography of two cosmopolitan families of flowering plants: Annonaceae and Rhamnaceae

Annonaceae are a pantropically distributed family found predominantly in rainforests, so they are megathermal taxa, whereas Rhamnaceae are a cosmopolitan family that tend to be found in xeric regions and may be classified as mesothermal. Phylogenetic analyses of these families are presented based on rbcL and trnL-F plastid DNA sequences. Likelihood ratio tests revealed rate heterogeneity in both phylogenetic trees and they were therefore made ultrametric using non-parametric rate smoothing and penalized likelihood. Divergence times were then estimated using fossil calibration points. The historical biogeography of these families that are species rich in different biomes is discussed and compared with other published reconstructions. Rhamnaceae and most lineages within Annonaceae are too young to have had their distribution patterns influenced by break-up of previously connected Gondwanan landmasses. Contrasts in the degree of geographical structure between these two families may be explained by differences in age and dispersal capability. In both groups, long-distance dispersal appears to have played a more significant role in establishing modern patterns than had previously been assumed. Both families also contain examples of recent diversification of species-rich lineages. An understanding of the processes responsible for shaping the distribution patterns of these families has contributed to our understanding of the historical assembly of the biomes that they occupy.     

The evolution of marine insects: phylogenetic, ecological and geographical aspects of species diversity in marine water striders

No other group of insects have been more successful in colonizing marine habitats than water striders and their allies (Heteroptera, Gerromorpha). More than 10% of the 1700 species of gerromorphan bugs are marine. Water striders have colonized the marine environment at least 14 times. The fossil records suggest that marine habitats were invaded by members of the families Veliidae and Gerridae earlier than 20-30 and 45 million years before present, respectively. Estuaries and mangrove swamps are undoubtedly the ancestral type of habitat, but water striders have diversified further in marine habitats including the surface of the open ocean (sea skaters. Halobates). Except for being obligatorily flightless, marine water striders are structurally very similar to their non-marine relatives. Physiological and behavioral rather than morphological specializations are likely to have been key innovations in the transition from limnic to marine habitats. The oldest and most species-rich clades originated in the Indo-West Pacific region. There are 3.5 times as many species of marine water striders in the Indo-West Pacific region than in the Atlantic/Caribbean/East Pacific region. This "diversity anomaly" is explained historically by region-specific differences in the origin and proliferation of clades, in paleoclimate and paleogeography, and in the propensity for dispersal between regions.     

Community structure of pollination webs of Mauritian heathland habitats

Pollination webs have recently deepened our understanding of complex ecosystem functions and the susceptibility of biotic networks to anthropogenic disturbances. Extensive mutualistic networks from tropical species-rich communities, however, are extremely scarce. We present fully quantitative pollination webs of two plant–pollinator communities of natural heathland sites, one of which was in the process of being restored, on the oceanic island of Mauritius. The web interaction data cover a full flowering season from September 2003 to March 2004 and include all flowering plant and their pollinator species. Pollination webs at both sites were dominated by a few super-abundant, disproportionately well-connected species, and many rare and specialised species. The webs differed greatly in size, reflecting higher plant and pollinator species richness and abundance at the restored site. About one fifth of plant species at the smaller community received <3 visits. The main pollinators were insects from diverse taxonomic groups, while the few vertebrate pollinator species were abundant and highly linked. The difference in plant community composition between sites appeared to strongly affect the associated pollinator community and interactions with native plant species. Low visitation rate to introduced plant species suggested little indirect competition for pollinators with native plant species. Overall, our results indicated that the community structure was highly complex in comparison to temperate heathland communities. We discuss the observed differences in plant linkage and pollinator diversity and abundance between the sites with respect to habitat restoration management and its influence on pollination web structure and complexity. For habitat restoration to be successful in the long term, practitioners should aim to maintain structural diversity to support a species-rich and abundant pollinator assemblage which ensures native plant reproduction.     

Seasonal Incidence and Diversity Pattern of Avian Communities in the Bangalore University Campus,India

The present study deals with the species abundance, diversity and species richness of avian communities in the Bangalore University Campus (BUC), Bengaluru, India. One hundred and six species of birds belonging to 42 families under 68 genera were recorded. Shannon–Wiener’s and Fisher’s alpha diversities, species evenness, species richness of bird communities, number of bird species and percentage of population density of birds between various seasons in the BUC differed significantly between the study years. Of these bird species, the relative abundance (6.96 %) and species distribution ratio (0.070) of Psittacula krameri were highest, whereas relative abundance (0.04 %) and species distribution ratio (0.002) of Coracias benghalensis were lowest. The existing 32 species of flowering plants/trees belonging to 29 genera under 14 families in the campus are used for perching by birds. Moreover 29 species of flowering plants/trees belonging to 24 genera under 16 families depend on birds for pollination and/or seed dispersal. Occurrence of greater bird diversity and abundance of avian communities were recorded highest in the winter season in the BUC premises. In the different seasons, the BUC had varying community structure of birds between the study years. BUC suffers from numerous threats namely grass cutting, fire and grazing of domestic animals. Conservation methods needed for habitat management are restoration of vegetation and wetlands, and increase plant and tree diversity to protect the ecosystem of BUC habitat and to preserve its diversity of avifauna.     

The fossil record and macroevolutionary history of the beetles

Coleoptera (beetles) is the most species-rich metazoan order, with approximately 380 000 species. To understand how they came to be such a diverse group, we compile a database of global fossil beetle occurrences to study their macroevolutionary history. Our database includes 5553 beetle occurrences from 221 fossil localities. Amber and lacustrine deposits preserve most of the beetle diversity and abundance. All four extant suborders are found in the fossil record, with 69% of all beetle families and 63% of extant beetle families preserved. Considerable focus has been placed on beetle diversification overall, however, for much of their evolutionary history it is the clade Polyphaga that is most responsible for their taxonomic richness. Polyphaga had an increase in diversification rate in the Early Cretaceous, but instead of being due to the radiation of the angiosperms, this was probably due to the first occurrences of beetle-bearing amber deposits in the record. Perhaps, most significant is that polyphagan beetles had a family-level extinction rate of zero for most of their evolutionary history, including across the Cretaceous–Palaeogene boundary. Therefore, focusing on the factors that have inhibited beetle extinction, as opposed to solely studying mechanisms that may promote speciation, should be examined as important determinants of their great diversity today.     

PHYLOGENETIC ANALYSIS OF TRAIT EVOLUTION AND SPECIES DIVERSITY VARIATION AMONG ANGIOSPERM FAMILIES

Angiosperm families differ greatly from one another in species richness (S). Previous studies have attributed significant components of this variation to the influence of pollination mode (biotic/abiotic) and growth form (herbaceous/woody) on speciation rate, but these results suffer difficulties of interpretation because all the studies ignored the phylogenetic relationships among families. We use a molecular phylogeny of the angiosperm families to reanalyse correlations between S and family-level traits and use reconstructions of trait evolution to interpret the results. We confirm that pollination mode and growth form are correlated with S and show that the majority of changes in pollination mode involved a change from biotic to abiotic pollination with an associated fall in speciation rate. The majority of growth form changes involved the evolution of herbaceousness from woodiness with a correlated rise in speciation rate. We test the hypothesis of Ricklefs and Renner (1994) that “evolutionary flexibility” rather than other trait changes triggered increased speciation rates in some families, but find little support for the hypothesis.     

Dynamics of species-rich upland hay meadows over 15 years and their relation with agricultural management practices

Questions: Has the species-rich vegetation of upland hay meadows been maintained under low intensity management imposed by an agri-environment scheme? Is the target plant community re-establishing where it has been modified previously by intensive agricultural practices? What combinations of management practices and soil properties are associated with changes towards or away from the target community? Location: The Pennines, northern England, UK. Methods: A survey of 116 hay meadows in 1987 was repeated in 2002 by recording plant species in permanent quadrats. Changes in community variables (species richness, Ellenberg values, upland hay meadow community coefficients) were analysed in species-rich, modified species-rich and degraded grassland types. Redundancy Analysis and Generalised Linear Models were used to show the relationship between management practices and soil properties and change in species composition and community variables. Results: Few sites contained the species-rich grassland type, and here forb richness declined. In the modified species-rich type, total and grass species richness increased but Ellenberg N-values also increased. Total and grass species richness increased in the degraded type and the community coefficient increased. Management was weakly related to change in species composition but showed clear relationships with the community variables. Re-establishment of the target species-rich community was more likely with late cutting, in the absence of cattle or prolonged spring grazing, and at lower soil nutrient status. Conclusion: The species-rich community was not maintained but some reversion occurred in degraded grassland. Inorganic fertiliser application and intensive spring grazing should be avoided and cutting delayed until late July.     

Contrasting flowering phenology and species richness in abiotically and biotically pollinated angiosperms

Abstract Biotic pollination is thought to correlate with increased interspecific competition for pollination among plants and a higher speciation rate. In this study we compared patterns of flowering phenology and species richness between abiotically (wind) and biotically pollinated plants, using phylogenetically independent contrasts. We compiled phenological data from eight local seasonal floras, in which we found geographically overlapping sister clades. Of 65 documented origins of wind pollination, we were able to use up to 17 independent contrasts. In contrast to previous studies we found no difference in global species richness between wind- and biotically pollinated sister clades. Regarding phenology, we found wider phenological spread in biotically pollinated clades, earlier flowering onset in wind-pollinated trees, but no difference in duration of flowering between pollination modes. These results corroborate previous views that niche space is more constrained for wind-pollinated species, and that niche partitioning is less important between wind-pollinated plants compared to plants pollinated by animals.     

Phylogenetic conservatism and biogeographic affinity influence woody plant species richness–climate relationships in eastern Eurasia

Mechanisms underlying species richness patterns remain a central yet controversial issue in biology. Climate has been regarded as a major determinant of species richness. However, the relative influences of different evolutionary processes, (i.e. niche conservatism, diversification rate and time for speciation) on species richness–climate relationships remain to be tested. Here, using newly compiled distribution maps for 11 422 woody plant species in eastern Eurasia, we estimated species richness patterns for all species and for families with tropical and temperate affinities separately, and explored the phylogenetic signals in species richness patterns of different families and their relationships with contemporary climate and climate change since the Last Glacial Maximum (LGM). We further compared the effects of niche conservatism (represented by contemporary-ancestral climatic niches differences), diversification rate and time for speciation (represented by family age) on variation in the slopes of species richness–climate relationships. We found that winter coldness was the best predictor for species richness patterns of most tropical families while Quaternary climate change was the best predictor for those of most temperate families. Species richness patterns of closely-related families were more similar than those of distantly-related families within eudicots, and significant phylogenetic signals characterized the slopes of species richness–climate relationships across all angiosperm families. Contemporary-ancestral climatic niche differences dominated variation in the relationships between family-level species richness and most climate variables. Our results indicate significant phylogenetic conservatism in family-level species richness patterns and their relationships with contemporary climate within eudicots. These findings shed light on the mechanisms underlying large-scale species richness patterns and suggest that ancestral climatic niche may influence the evolution of species richness–climate relationships in plants through niche conservatism.     

Introduction and synthesis: Plant phylogeny and the origin of major biomes

Phylogenetic trees based upon DNA sequence data, when calibrated with a dimension of time, allow inference of: (i) the pattern of accumulation of lineages through time; (ii) the time of origin of monophyletic groups; (iii) when lineages arrived in different geographical areas; (iv) the time of origin of biome-specific morphologies. This gives a powerful new view of the history of biomes that in many cases is not provided by the incomplete plant fossil record. Dated plant phylogenies for angiosperm families such as Leguminoaceae (Fabaceae), Melastomataceae sensu stricto, Annonaceae and Rhamnaceae indicate that long-distance, transoceanic dispersal has played an important role in shaping their distributions, and that this can obscure any effect of tectonic history, previously assumed to have been the major cause of their biogeographic patterns. Dispersal from other continents has also been important in the assembly of the Amazonian rainforest flora and the Australian flora. Comparison of dated biogeographic patterns of plants and animals suggests that recent long-distance dispersal might be more prevalent in plants, which has major implications for community assembly and coevolution. Dated plant phylogenies also reveal the role of past environmental changes on the evolution of lineages in species-rich biomes, and show that recent Plio-Pleistocene diversification has contributed substantially to their current species richness. Because of the critical role of fossils and morphological characters in assigning ages to nodes in phylogenetic trees, future studies must include careful morphological consideration of fossils and their extant relatives in a phylogenetic context. Ideal study systems will be based upon DNA sequence data from multiple loci and multiple fossil calibrations. This allows cross-validation both of age estimates from different loci, and from different fossil calibrations. For a more complete view of biome history, future studies should emphasize full taxon sampling in ecologically important groups, and should focus on geographical areas for which few species-level phylogenies are available, such as tropical Africa and Asia. These studies are urgent because understanding the history of biomes can both inform conservation decisions, and help predict the effects of future environmental changes at a time when biodiversity is being impacted on an unprecedented scale.     

Humans,bees, and pollination services in the city: the case of Chicago,IL (USA)

Despite the global trend in urbanization, little is known about patterns of biodiversity or provisioning of ecosystem services in urban areas. Bee communities and the pollination services they provide are important in cities, both for small-scale urban agriculture and native gardens. To better understand this important ecological issue, we examined bee communities, their response to novel floral resources, and their potential to provide pollination services in 25 neighborhoods across Chicago, IL (USA). In these neighborhoods, we evaluated how local floral resources, socioeconomic factors, and surrounding land cover affected abundance, richness, and community composition of bees active in summer. We also quantified species-specific body pollen loads and visitation frequencies to potted flowering purple coneflower plants (Echinacea purpurea) to estimate potential pollination services in each neighborhood. We documented 37 bee species and 79 flowering plant genera across all neighborhoods, with 8 bee species and 14 flowering plant genera observed on average along each neighborhood block. We found that both bee abundance and richness increased in neighborhoods with higher human population density, as did visitation to purple coneflower flower heads. In more densely populated neighborhoods, bee communities shifted to a suite of species that carry more pollen and are more active pollinators in this system, including the European honey bee (Apis mellifera) and native species such as Agapostemon virescens. More densely populated neighborhoods also had a greater diversity of flowering plants, suggesting that the positive relationship between people and bees was mediated by the effect of people on floral resources. Other environmental variables that were important for bee communities included the amount of grass/herbaceous cover and solar radiation in the surrounding area. Our results indicate that bee communities and pollination services can be maintained in dense urban neighborhoods with single-family and multi-family homes, as long as those neighborhoods contain diverse and abundant floral resources.