Publications on pollination ecology

1979. Revision de los Xeromelissinae Chilenos (Hymenoptera, Colletidae). An. Mus. Nac. Hist. Nat. Chile 12: 95-182. (Toro H, Moldenke AR).

ABSTRACT: Four genera of Xeromelissinae are present in Chile according to this paper: Xeromelissa, Chilicola, Xenochilicola, and Chilimelissa.
Xeromelissa Cockerell is known from only one species from Peru and the north of Chile. Chilicola Spinola includes the following subgenera: Chilicola s.str. (four species)Chilioedicelis n. subgen. (three species), Oediscelis Philippi (two species), Heteroediscelis n. subgen. (13 species), Anoediscelis n. subgen. (three species), Stenoediscelis n. subgen. (two species), Idioprosopis Meade-Waldo (three species); no subgeneric status is given for Chilicola hahni Herbst, C. longitarsa and C. gutierrezi Moure. Xenochilicola n. genus includes three species from north and central Chile. Chilimelissa n. genus, widely distributed throughout Chile, includes twelve species. Of the 49 species considered in this paper 38 are described as new.

1979. Host-plant coevolution and the diversity of bees in relation to the flora of North America. Phytologia 43: 357-419. (Moldenke AR).

CONCLUSIONS:
I. The host-association data base of North American bees is sufficient for tentative conclusions regarding many important aspects of host- plant specialization patterns.
II. There is only a 3-fold difference in bee species richness in the major phytogeographic realms of North America (excluding the depauperate tundra).
   a) the high California bee diversity is in some ways an artifact of artificial political boundaries.
   b) Great Basin and Southern Mixed Forest support fewest bee species; mediterranean California and desert support most bee species.
III. There is only a 3-fold difference in bee species richness between geographic regions of California.
   a) cismontane southern California, southern Sierra Nevada and southern Coast Ranges are species rich; northern montane and coastal are species poor.
IV. There is not a clear species/area relationship underlying conclusion II. Bee species per area varies about 6-fold (excluding tundra), unrelated to possible simple correlations, but is an additional order of magnitude greater in mediterranean California.
V. True host specialization and host shifts have occurred about 250 times within the North American bee fauna.
   a) nearly all ancestral stocks are primitively polylectic; nearly all diet changes are from polylectic to specialist. There are no known specialist to polylectic switches; such switches are apparently therefore one-way changes only.
   b) considering the diversity of the North American flora and North American bees in general, this is a surprisingly small number of host changes, relative to the number of common North American melittophilous plant genera not supporting specialist pollinators.
   c) most such shifts onto a novel plant are not particularly successful, measured in terms of subsequent adaptive radiation;
   d) some immigrant phyletic lineages have entered the United States as specialists and have remained so on the same plants;
   e) the two largest genera of North American bees are characterized by the highest levels of host-specialization; the third largest by perhaps none at all;
   f) only 53 switches are known from specialist on plant genusA to specialist on plant genusB (A not confamiliar with B). Nearly all true host switches take place in the southwestern deserts or mediterranean California (equally); this type of host switch is characteristic primarily of Nomadopsis and Perdita (Pygoperdita);
   g) few host switches are between visually similar taxonomically unrelated plants; few (except poorly documented Compositae) between very dissimilar but confamilial plants; most between groups without distinct characters in common--sometimes the switch is to a dominant community member, sometimes to the only synchronous bloomer, many unexplicated.
VI. Arctotertiary- and Neotropical-associated bee lineages have contributed about equally to pollination ecology relations in arid/semi-arid western plants. Range expansions into close association with a novel geoflora is usually by polyleges, or by specialists which are already associated with an invading plant genus, but occasionally by host shifts presumably onto a novel host in a region of parapatry. Nearly all such shifts have been from Arctotertiary to Madrotertiary floras; only two from Madrotertiary to Arctotertiary.
VII. Most specialist-feeding bees in North America are oligolectic on Compositae and legumes. More species are associated with Phacelia than any other genus. Most plant genera with obligate specialist pollinators have coevolved with only 1-3 lineages and less than 10 species.
VIII. Bees tend to coevolve specialist-feeding relationships with plants which:
   a) tend to bloom only early in the morning or late in the evening;
   b) those which bloom at the onset or close of the anthesis season for that particular community;
   c) are community dominants;
   d) plants with unusual floral morphologies (i.e., thin tubular corollas, extremely large or small pollen grains, pendant blossoms and unusually tiny flowers).
IX. The percentage of specialist-feeding bees on a faunistic basis varies from ca. 15-50%;
   a) percentage of specialist-feeders is positively correlated to total bee diversity;
   b) highest percentages occur in Mediterranean California and the desert; lowest in eastern Deciduous forests;
   c) the total number of plant genera with coevolved specialists in biotic realms of North America is also positively correlated to total bee diversity (but is disproportionately highest in med. California);
   d) oligolectic "specialists-to-the-family-level" are negatively correlated to total species diversity within the floristic provinces of North America and within geographic regions within California.

1979. Pollination ecology as an assay of ecosystemic structure: convergent evolution in California and Chile. Phytologia 42: 415-454. (Moldenke AR).

SUMMARY: Diversity and feeding specialization (with/without niche overlap) of pollinating insects was examined at 0.5 km2 sites along transects including analogous physiognomic plant communities in California and Chile. Though climates at the analogous community sites are similar, plant diversity (H and species count) patterns differ due to the prevalence of fire in the California sclerophyll scrub. Treating the distinct floras of the fire cycle additively, plant diversities of similar communities compared intercontinentally are more similar than within-country diversity comparisons of adjacent communities. The diversity of all taxonomic groups of pollinators manifests consistently greater intercontinental analogue similarity than compared to different physiognomic communities within the same country. All pollinator groups are more diverse in California due to the larger area and the presence of more diverse refugia from Pleistocene glaciation. Similar percentages of the resident flora of analogue communities rely upon wind, insect and self-pollination, whereas adjacent but different communities may differ markedly; the same analogous relations hold for the component pollinator groups with the exception of syrphid flies. Utilization strategies exhibit emphasis on generalists (by species) in maritimal and Mediterranean scrub environments; emphasis on generalists (by individuals) in the Mediterranean scrub; emphasis on feeding specialists (by species and individuals) in the desert; and emphasis on very few species of abundant generalist feeders in the cool forest and maritime environments of both countries. Results are commensurate with the hypothesis that climate controls the phenological presentation of floral resources and that these in turn determine the abundance and diversity of floral herbivores in optimized patterns irrespective of a completely distinct evolutionary heritage within the two continents.

1979. Pollination ecology in montane Colorado: a community analysis. Phytologia 42: 349-379. (Moldenke AR, Lincoln PG).

ABSTRACT: Synecological pollination studies of communities in montane Colorado revealed very low species richness of all types of pollinators although flowers were abundant. In every community less than 8% of the non-wind-pollinated p[lant species attract more than 60% of the resident vector species. A large majority of the pollinator individuals in each of the five communities are generalist feeders; bumblebees are preeminent in all environments and muscoid flies are prominent in the alpine tundra and forests. In all communities selfing as the habitual mode of reproduction is very frequent (20% of the total flora), and increases to 48% of the flora in the alpine tundra. Pollinators are most abundant in the physiognomically open fescue grassland, sage and alpine tundra communities, but are most diverse in the lower altitude grassland and sage. Pollinators are least abundant and diverse in the aspen and spruce-fir forest communities. Specialist pollinators comprise 8% to 22% of the total resident pollinators; specialist species are two to five times richer in the open communities than in the forests. Pollination characteristics of the five communities parallel results obtained in subalpine and alpine California.

1979. Pollination ecology in the Sierra Nevada. Phytologia 42: 223-282. (Moldenke AR).

SUMMARY: Competition between plants for pollinators increases the blooming season for plant species in pollinator-limited environments, thus increasing the percentage of the flora that is blooming during any given week. Perennials, then have a premium on blooming immediately following the dormant season. In communities that are not seriously pollinator-limited, floral initiation time is not pulsed and rather conforms to the Central Limit Theorem, implying independent control on the flowering phenology of each species. As the total length of permissible blooming season lengthens, the peak of maximum synchronous bloom is delayed. The peak in total available community floral biomass is not always correlated to maximum number of species in bloom; additionally, some of the least important contributants to community floral biomass are the most heavily visited by pollinators and vice-versa. Though annual plants as a group might be expected to differ significantly from perennial plants in the timing of their blooming season, in fact they do not.
Though competition for pollinators in communities with progressively more total species would be expected to produce a larger percentage of self-compatible species ("the losers") at the peak of the bloom and a larger emphasis on exclusion floral morphologies (the winners, or the ones that can afford an insurance policy), this in fact does not take place. The total percentage of all self-compatible species in a community is determined by community type. The percentage of species with exclusion flowers of the total species is apparently consistent in all Sierra Nevada communities.
Within all communities the proportion of genetically self- compatible species that is in fact unvisited by pollinators and therefore has to habitually self is highest at the peak of synchronously blooming species. Additionally, this competition for pollinators is revealed in the disproportionate occurrence of genetically incompatible annual species flanking the anthesis peak, while the disproportionate abundance of self-compatible perennial species occurs at the anthesis peak.
Plant communities which are pollinator-limited have much fewer total entomophilous and ornithophilous species at the peak of anthesis, since a larger percentage of the community species total is wind-pollinated; the precise number of successfully animal-vectored species in a community varies widely and does not cluster about a particular limit independent of community type. A mechanism which permits the successful synchronous outcrossing at the peak of bloom is the disproportionate number of plants serviced by specialist-feeding bees; this allows efficient pollination even when in low density or when competing species may have successfully usurped all the generalist pollinators. Specialist-feeding habits of course would not evolve in bees, if it were not competitively forced upon them by competition for their floral resources as well; more species of specialist-feeding bees are in fact active during the peak synchrony of anthesis than at any other period.
Most of the species of bees native to the Sierra Nevada are in fact rather widespread throughout mountainous western United States, and endemicity is very low. Bee species endemic to montane California and with phylogenetic lineages traceable to California itself or desert southwestern USA are largely specialized in their feeding habits. They demonstrate four patterns of coevolutionary host specialization and switching: specialist-feeding species on hosts with relatives on congeneric hosts in adjacent areas; specialist-feeders on plant genera commonly associated with many specialist-feeding groups, evolved directly from generalist feeders; specialist-feeders on different genera with different anthesis times within the same plant family; and specialists on species of plants blooming synchronously with the original hosts, but taxonomically and morphologically distinct.

1977. Reproductive systems of Larrea. IN: Creosote bush: biological chemistry of Larrea in New World deserts. Mabry TJ, Hunziker JH & Difeo DR, eds. pp. 92-114. (Simpson BB, Neff JL, Moldenke AR).

SUMMARY: All five species of Larrea have the same floral pattern of cup-shaped yellow flowers with five free petals, ten anthers, and a superior globose ovary. They differ in the size of their flowers and the degree to which the anthers reach and are appressed to the stigmas. Experimental data and floral morphology suggest that these differences are related to the amount of natural self-pollination. Experiments have shown that all of the species are self-compatible but that L. tridentata (tetraploid), L. cuneifolia, and L. divaricata exhibit an increasing series in their levels of natural self- pollination. Floral morphology of L. nitida and L. ameghinoi indicates that they depend heavily on self-pollination. The dominance of Larrea in New World desert scrub ecosystems and the resultant relative abundance of flowers make Larrea an important source of food for floral herbivores. Both pollen and nectar are offered by the five species as rewards for potential pollen vectors, but the relative amounts of each produced appear to depend on the rewards of the flowers of sympatric, synchronously blooming species. Although a variety of animals visit the flowers, bees are the most abundant and diverse group of floral visitors in all Larrea desert areas and are undoubtedly the most important pollinators of the creosote bush. At the two IBP desert scrub study sites, the Larrea bee faunas are, for the most part, taxonomically unrelated, but show convergence in the number of species considered to be major pollen vectors (16 in Andalgala; 13 at Silver Bell) and in the number of obligate specialists on Larrea (6 in each area). In addition, the two bee faunas show convergence in temporal and behavioral foraging patterns that permit their coexistence on the same floral host.

1977. Prosopis flowers as a resource. IN: Mesquite: its biology in two desert ecosystems. BB Simpson ed. pp. 84-107. (Neff JL, Moldenke AR, Simpson BB).

SUMMARY: As would be expected, the abundance of flowers, their copious amounts of nectar and pollen, and the lack of any morphological structures preventing access to these resources has led to the exploitation of Prosopis inflorescence by a wide array of animals, particularly bees. Various animals use the flowers as food, consuming only the pollen and/or nectar, or even frequenting the inflorescence only as mating or hunting sites. Most of these animal groups are unrelated between the two hemispheres.
The predictability with which Prosopis blooms in our two desert study areas has been a contributing factor in the specialization of many species of bees for mesquite flowers. Competition among these specialists has led to a variety of temporal, spatial, and mechanical displacements in foraging behavior. Convergent patterns of foraging behavior are found in the bees of the two desert areas.
Despite the high visitation rates, however, most ovaries never begin to mature. It is probable that hormonal inhibition rather than the lack of successful pollination causes this low fruit set relative to the number of flowers produced. Still, successful maturation of an ovary does not insure a successful seed crop. Both immature ovaries and ripe pods are subject to predation by a large number of desert scrub vertebrates and insects. While the maturation of fruits constitutes a second step in the reproductive cycle of Prosopis, it provides at the same time a potential food source for many organisms that has been actively exploited both by animals and man in deserts of North and South America.

1977. Flowers -- flower visitors system. IN: Convergence in warm desert ecosystems. Orians GH & Solbrig OT, eds. pp. 165-224. (Moldenke AR, Simpson BB, Neff JL).

1977. Convergent evolution in the consumer organisms of mediterranean Chile and California. IN: Convergent evolution in Chile and California: mediterranean climate ecosystems. Mooney HA, ed. pp. 144-192. (Cody ML, Fuentes ER, Glanz W, Hunt JH, Moldenke AR).

1977. The origin of the biota. I: Convergent evolution in Chile and California: mediterranean climate ecosystems. Mooney HA, ed. pp.13-26. (Cody ML, Fuentes ER, Glanz W, Hunt JH, Moldenke AR, Solbrig OT).

1976. Pollination ecology. IN: The mediterranean scrub ecosystems of California and Chile: a synthesis. Thrower NJW & Bradbury DE, eds. pp. 199-217. (Moldenke AR).

1976. Evolutionary history and diversity of the bee faunas of Chile and Pacific North America. Wasmann J. Biol. 34: 147-178. (Moldenke AR).

SUMMARY: A study of the bee faunas of Pacific western North America and Chile was undertaken to study the effects of similar climatic patterns on the evolutionary radiation of bees and on behavioral patterns of resource utilization. Chile has been isolated from source areas since the Mesozoic orogeny of the Andes and the formation of the Atacama Desert. The Pacific regions of North America are much more broadly connected with potential source areas for colonization from Asia, the Neotropics, and Europe by way of arctic Canada. Bee speciation occurs most rapidly in arid and semiarid regions; these regions in North America are more extensive, and immigration of taxa throughout the region is not hampered to the extent that the Andes isolate Chilean deserts from Argentine deserts. A much larger endemic semiarid bee fauna consequently inhabits California. Indeed, bee diversity is higher in Pacific North America in all biotic regions. Comparison of levels of species diversity within 0.5 km2 sites in both regions reveals comparable localized species packing in a series of community types in opposing hemispheres. Plant communities with the lowest levels of bee diversity characteristically have the fewest individuals and, with the exception of the desert, are characterized by generalist feeding tendencies as well. In the deserts of both countries, total faunistic diversity is high, but response to localized rains is by a small number of taxa, most of which are obligately specialized and coevolved with one particular flowering plant taxon.

1976. California pollination ecology and vegetation types.
Phytologia 34: 305-361. (Moldenke AR).

SUMMARY: Synecological analyses of pollination ecology have been initiated only recently. Nevertheless, studies have shown conclusively that in some vegetation types (e.g., alpine tundra, subalpine marsh- meadow, subalpine forest, northern coastal scrub, coastal sage, maritimal dunes, redwood forest, and mixed evergreen forest) most plant species are pollinator limited and must compete for visitation by vectors which are generalist feeders and must be supplied with a sufficient reward to ensure subsequent visits to the same plant species. In chaparral, valley grassland, warm desert, weed, and open forest communities, pollinators are usually very abundant and flower visitation is assured; specialist pollinators are abundant in these environments. However, those perennial plants that require outcrossing still must rely upon large-bodied, far-ranging generalist pollinators to achieve efficient interplant pollen flow.
Though many of the interrelations between plants and their pollinators have now been tentatively delineated, we know little of the ecological and evolutionary significance of different modes of pollination. Unquestionably, valid representations can be made of community-wide phenomena as they occur in various localities throughout the state. It must be remembered, however, that the pollination of any one particular plant species is subject to considerable variability depending upon circumstance. Since the energetic and nutritive reward of the floral attractants is genetically determined and not subject to modification by the immediate competitive environment of a plant individual, competition patterns for vectors may have significantly different outcomes locally; some cornucopia species may be barren of vectors and some habitually selfed species may be heavily outcrossed. Knowledge of the patterns of pollination interactions within differing vegetation types now permits us to assess the roles of these pollination syndromes in the evolution of our native plant communities.

1975. Convergence in vegetation structure along analogous climatic gradients in California and Chile. Ecology 56: 950-957. Parsons D, Moldenke AR).

ABSTRACT: A series of plant communities along analogous climatic gradients in southern California and central Chile has been analyzed to determine the extent of convergence in a variety of ecologically significant characters. Results show that, despite distinct genetic histories, the structure of the vegetations of these areas has converged under similar climatic constraints. Such characters as species richness, growth form, leaf duration, leaf size, and spines are quantitatively more similar between floristically distinct yet climatically analogous sites on the two continents than between floristically similar but climatically distinct sites a short distance apart on the same continent. Such findings, which hold true for both the native woody vegetation and the partially exotic herbaceous understory, provide quantitative support for the general hypothesis that plant form and community structure are highly determined, regardless of genetic constraints, by environmental parameters.

1975. Niche specialization and species diversity along a California transect. Oecologia 21: 219-242. (Moldenke AR).

SUMMARY: The structure of the food-web at the flower-herbivore interface was examined along a transect of fourteen communities across central California. All results are commensurate with the hypothesis that in most environments there is selective pressure towards specialization. However, it is only in the most predictable and stable environments that the resultant diminishment of behavioral and genetic flexibility is in a sense "permitted" by subsequent natural selection. In the most extreme environments, behavioral specialization may be a necessary prerequisite permitting briefly thriving ephemeral populations which must recolonize frequently. The data results indicate: 1) Total species number increases with stability and predictability of the climate; 2) As the climate ameliorates, niche- specialization is a progressively more successful strategy; 3) The percentage of niche-specialized species of both plants and flower- feeding herbivores increases in the most severe environments at the expense of the more moderately specialized species; 4) Energetic flow chart redundancy increases in extreme environments; 5) Especially important to an understanding of pollination interactions is the fact that similar physiognomic communities at very different altitudes are in all cases much more similar than different community types within a research site.

1974. The bees of California: a catalogue with special relevance to pollination and ecological research. Volumes I-VI. International Biological Program Structure and Origin of Ecosystems Technical Reports 74-1 through 74-6. 1073 pp. (A. Moldenke & J. Neff)

1974. Studies on the pollination ecology and species diversity of native California plant communities. Volumes II-III. International Biological Program Structure and Origin of Ecosystems Technical Reports 74-13 & 74-14, 412 pp.

1974. Studies on the pollination ecology and species diversity of natural Chilean plant communities. International Biological Program Structure and Origin of Ecosystems Technical Report 74-18, 135 pp. (A.R. Moldenke & J. Neff).