• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 636
  • 283
  • 146
  • 146
  • 146
  • 146
  • 146
  • 145
  • 66
  • 24
  • 2
  • 1
  • Tagged with
  • 1286
  • 1286
  • 215
  • 165
  • 138
  • 129
  • 116
  • 116
  • 116
  • 108
  • 106
  • 105
  • 68
  • 66
  • 56
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
21

THE PHENOLOGICAL RELATIONSHIPS OF MALE EUGLOSSINE BEES (HYMENOPTERA: APIDAE) AND THEIR ORCHID FRAGRANCE HOSTS

Unknown Date (has links)
The orchid-male euglossine bee interaction is mutualistic. The bees pollinate the orchids which provide floral fragrance rewards. I sought evidence for an unambiguous, obligatory, coevolved interaction on the basis of their seasonal and geographic relationships. / Male euglossine bee activity and orchid flowering phenology were monitored for over a year on Barro Colorado Island (BCI) and two other lowland sites in central Panama. Weekly censuses at chemical fragrance baits revealed seasonal changes in bee species richness and abundance; however, other community attributes were relatively constant. Peak activity was from February through June. Variation between the lowland sites was minor. The seasonal patterns were probably the result of local eclosion events. / The flowering phenologies of orchid fragrance hosts were season-dependent. The overall blooming patterns were similar to changes in bee abundance and species richness. / Orchids tapped the majority of euglossine species and individuals for pollinator services each season. Most of those bee species that temporarily lacked orchid fragrance hosts in bloom persisted in the area, continually eclosed from nests, and sought floral fragrance compounds. General geographic distributions of all orchid-pollinator pairs were not mutually inclusive. Nearly a third of the bee species were not pollinators of any local orchid fragrance host. Alternative fragrance sources existed. Thus, bee activity could be independent of orchid fragrance supplies. / There was no evidence for an obligatory, coevolved mutualism. The orchids probably exploited a preexisting behavioral phenomenon of their euglossine pollinators, and have had no obvious effect on their evolution. / Source: Dissertation Abstracts International, Volume: 42-03, Section: B, page: 0891. / Thesis (Ph.D.)--The Florida State University, 1981.
22

Ecomorphology and foraging behavior of the yellow warbler (Dendroica petechia)

Unknown Date (has links)
Populations of permanent resident "Mangrove" and migratory "Yellow" forms of the insectivorous Yellow Warbler (Dendroica petechia) occur together in mangrove woodlands along the coasts of Middle America in winter. "Mangrove" Warblers are larger than "Yellow" Warblers, with proportionately longer bills, more rounded wings, and shorter legs. "Yellow" Warblers in the temperate zone use aerial foraging techniques more than "Mangrove" Warblers. In winter, "Yellow" Warblers shift their foraging behavior from their breeding pattern towards that of the "Mangrove" Warblers. / Based on intraspecific morphological differences, I made predictions about foraging differences between the two forms, and these predictions were tested by field observations of the two forms when they occurred together in mangrove habitat. As predicted, "Mangrove" Warblers were more adept at flying through the foliage and they foraged more slowly than did "Yellow" Warblers. However, "Mangrove" Warblers did not use aerial foraging actions more than the "Yellow" Warblers did, contrary to the predictions. / The predictions were also tested in a more controlled situation, in which wild-caught birds were used in aviary experiments. In this situation, "Mangrove" Warblers hovered longer and held their bodies more horizontally than did the "Yellow" Warblers. Because of the differences in body angle, "Mangrove" Warblers were able to hover closer to a vertical surface without their wing tips striking it, than could the "Yellow" Warblers. / The superior hovering ability of the "Mangrove" Warblers, detected only in the aviary experiments, confirmed predictions based on morphological comparisons, in spite of the fact that the differences were not evident from field observations even when the two forms occurred in one habitat. In fact, if only "Yellow" Warblers in the temperate zone and "Mangrove" Warblers had been compared, the predictions on foraging action would have been contradicted. To analyze ecomorphological problems it is necessary to minimize confounding factors. Even then, experiments may be necessary to fully understand ecomorphological relationships. / Source: Dissertation Abstracts International, Volume: 49-12, Section: B, page: 5126. / Major Professor: Frances C. James. / Thesis (Ph.D.)--The Florida State University, 1988.
23

Experimental study of geographic variation in reproductive and developmental traits of Mallard ducks

Unknown Date (has links)
The classical model of the process that maintains intraspecific geographic variation in birds is that phenotypic differences seen in nature reflect genetic adaptations of populations to local environmental conditions and that they are being maintained by natural selection. Wildlife biologists, on the other hand, have usually assumed that, because of the lack of site fidelity among males to breeding areas, many populations of waterfowl are not genetically differentiated. In an attempt to elucidate the genetic and environmental components of geographic variation in reproductive and developmental traits between two populations of Mallard ducks (Anas platyrhynchos), one in southern Manitoba and one in central California, I conducted several experiments. / By monitoring the reproductive performance of wild birds from the two regions reared in common environment under controlled photoperiods in captive conditions, I found that the earlier laying date and lower clutch size observed in nature in the California population are primarily attributable to environmental influences. In addition, there are underlying genetic differences in clutch size between the populations that run counter to differences observed in the wild. Egg size did not differ between populations in the wild or in the common environment. / When reared in a common environment, birds from the wild California population fledged at a younger age than those from Manitoba. These differences disappeared among offspring from captive breeding crosses, reared in a common environment, suggesting that variation in growth rates between the populations in the wild is environmentally induced. When young from eggs taken from the two wild populations were transplanted between localities at different times in the breeding season, some population differences were retained, but much of the variation in development could be attributed to differences in nesting phenology and local environmental conditions. / These results suggest that most of the variation in reproductive and developmental traits between Mallard populations is environmentally induced. However, there is substantial genetic variation in traits within regions. / Source: Dissertation Abstracts International, Volume: 49-08, Section: B, page: 2992. / Major Professor: Frances Crews James. / Thesis (Ph.D.)--The Florida State University, 1988.
24

Interactions among three herbivores and their effects on a shared host plant

Unknown Date (has links)
For four years, I quantified the effects of three herbivores--a specialist chrysomelid beetle, Blepharida rhois, a specialist stem borer, Oberea ocellata, and whitetail deer--on the growth, mortality and fruit production of smooth sumac, Rhus glabra. I used selective exclosures to create ramets within a sumac clone that had different herbivore histories. Each year, the past history of a ramet was incorporated into herbivore treatments. I also documented how use of ramets by each herbivore related to previous attack by other herbivores. I found both negative and positive associations between species. Several experiments were designed to determine the underlying mechanisms behind these associations. / I found that chrysomelid herbivory significantly reduced ramet growth, survivorship and fruit production. These negative effects were persistent, lasting for a minimum of two years after attack had ceased. Deer browse was consistently associated with increased vegetative growth and sometimes with increased fruit production. These benefits of browse may be attributable to the selection by deer of larger ramets, rather than to positive effects of browse. There did not seem to be any strong interaction between beetle and deer attack in any year. Over four years, chrysomelid beetles exerted the strongest selective pressure on sumac both as a result of direct and indirect effects. Using common garden experiments, I determined that there were both plant genotypic and environmental factors contributing to sumac resistance to beetle attack. Because of this result, both diversifying and frequency-dependent selection could operate to maintain genetic variability in beetle resistance within the sumac population. / Source: Dissertation Abstracts International, Volume: 49-12, Section: B, page: 5126. / Major Professor: Daniel S. Simberloff. / Thesis (Ph.D.)--The Florida State University, 1988.
25

The ecology of epifaunal communities on prop roots of the red mangrove, Rhizophora mangle

Unknown Date (has links)
Invertebrate communities growing epifaunally on prop roots of red mangroves (Rhizophora mangle) were studied to determine what processes produce patterns of distribution and abundance. Root epifauna were compared among channels in a mangrove island in the Indian River, Florida. Except for flow rate, physical factors did not differ among channels and were not responsible for qualitative and quantitative differences in species' abundances. Neither did flow rate per se explain distributional patterns as survival of transplanted adults and early recruits was similar in channels experiencing very different flow. Epifaunal distributions are explained by patterns of larval supply and recruitment. Species with long-lived planktotrophic larvae were distributed evenly throughout the island. Species with short-lived lecithotrophic larvae were distributed heterogeneously with recruitment patterns and adult abundances reflecting locations of source populations and predominate flow patterns. / Dynamics of a mangrove root epifaunal community in the Florida Keys were studied for three years. Despite long-lived species, low recruitment rates, and little climatic seasonality, populations of the dominant epifauna showed large temporal fluctuations in abundance. Species commonly disappeared from roots and dominant species changed continually. The stochasticity of this community resulted from seasonal growth, predation, disturbance, and variable recruitment. / Comparisons of recruitment on ceramic tiles, wooden dowels, and Rhizophora roots revealed that caution must be used in modeling natural substrata with artificial surfaces. Artificial surfaces were useful, however, in answering ecological questions related to scale. / Eight mangrove root sponge species were tested for allelopathic effects on settling larvae. There was little evidence of recruitment inhibition for any species. On the contrary, recruitment of several species was higher in the presence of sponges. Flow effects and patchy larval supply were more important in structuring the communities than were allelopathic effects of resident sponges. / Dispersal of swimming and non-swimming larvae of the ascidian Ecteinascidia turbinata was compared. Swimming larvae traveled significantly shorter distances than non-swimming larvae. Swimming appeared to prevent advection of the larvae and enables populations to persist in a patchy mangrove habitat. / Source: Dissertation Abstracts International, Volume: 51-04, Section: B, page: 1611. / Major Professors: Craig M. Young; Richard N. Mariscal. / Thesis (Ph.D.)--The Florida State University, 1990.
26

BENTHIC ECOLOGY OF TIMBALIER BAY, LOUISIANA, AND ADJACENT OFFSHORE AREAS IN RELATION TO OIL PRODUCTION

Unknown Date (has links)
Source: Dissertation Abstracts International, Volume: 35-12, Section: B, page: 5755. / Thesis (Ph.D.)--The Florida State University, 1974.
27

EVOLUTIONARY ECOLOGY STUDIES ON SALAMANDERS OF THE GENUS DESMOGNATHUS. PART I: COMPETITIVE EXCLUSION ALONG A HABITAT GRADIENT BETWEEN TWO SPECIES OF SALAMANDERS (DESMOGNATHUS) IN WESTERN FLORIDA; PART II: LIFE HISTORY, GROWTH, AND BODY SIZE VARIATION IN POPULATIONS OF A STREAMSIDE SALAMANDER (DESMOGNATHUS BRIMLEYORUM) ON ADJACENT MOUNTAINS

Unknown Date (has links)
Source: Dissertation Abstracts International, Volume: 36-08, Section: B, page: 3753. / Thesis (Ph.D.)--The Florida State University, 1975.
28

COMPARATIVE COMMUNITY ORGANIZATION IN TROPICAL AND TEMPERATE SEA-GRASS (THALASSIA TESTUDINUM) MEADOWS

Unknown Date (has links)
Source: Dissertation Abstracts International, Volume: 37-07, Section: B, page: 3244. / Thesis (Ph.D.)--The Florida State University, 1976.
29

THE DIVERSITY OF TERRESTRIAL ARTHROPODS IN NORTHWEST FLORIDA SALT MARSHES

Unknown Date (has links)
Source: Dissertation Abstracts International, Volume: 38-05, Section: B, page: 2021. / Thesis (Ph.D.)--The Florida State University, 1977.
30

THE ROLE OF MATE GUARDING IN STONE CRABS

Unknown Date (has links)
The reproductive biology and residency patterns of over 800 stone crabs (Menippe mercenaria, M. adina, and their hybrid) were examined during an eight month tagging study at artificial, concrete block reefs constructed near intertidal oyster reefs and subtidal seagrass beds in Franklin and Wakulla Co., Florida. Characteristics of adult crabs occurring intertidally in the summer include a male-biased sex ratio (5M: 1F), a prevalence of M. adina and hybrids, a high frequency (71%) of molting males, and low sperm content (nine million) in males. Subtidally in the summer, the adult sex ratio was female-biased (1M: 9F), the Menippe-complex forms occurred at equivalent frequencies, and male sperm content was higher (18 million). In the fall, sex ratios became more uniform in both habitats, the intertidal male molting frequency declined (7%), and male sperm levels increased (19 million sperm). Mating among the Menippe-complex forms appeared random in both habitats. / A test of the effect of precopulatory guarding on sperm production in stone crabs revealed guarding males contained significantly more sperm (90-100 million) than non-guarding males exposed to pre-molt females or pre-molt males (40-50 million sperm). The sperm level for males held with intermolt females (20 to 30 million sperm) was consistent with background sperm levels from the field study. Male sperm number and the amount of sperm transferred to females were positively correlated. / The influence of sexual selection and predation on postcopulatory guarding durations in stone crabs was also examined. Males guarded significantly longer (126 h beyond the female's molt) when another male stone crab was present than when an intermolt female (84 h) or a blue crab (83 h) were present. In predation trials with the longest postcopulatory guarding durations, the females survived the treatment, whereas females were eaten by the blue crabs in the trials with the shortest guarding durations. The cul-de-sac morphology of the female sperm storage organ is such that sperm pre-emption is likely to occur upon multiple inseminations. Sexual selection appears important in maintaining postcopulatory mate guarding in stone crabs. / Source: Dissertation Abstracts International, Volume: 48-12, Section: B, page: 3486. / Thesis (Ph.D.)--The Florida State University, 1987.

Page generated in 0.0453 seconds