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- ItemThe Biology, Nutrition and Control of Formica exsectoides Forel(1945) Haviland, Elizabeth Edge; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)
- ItemThe Feeding Habits of the Toadfish (Opsanus Tau) Based on an Analysis of the Contents of the Stomach and Intestine(1951) Chrobot, Raymond J.; Littleford, Robert A.; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)Opsanus tau, (Linneaus) - the toadfish, inhabits a vast area along the Eastern Sea Coast of North America. It is found from the coast of Maine to the regions of the West Indies. North of Cape Cod, its occurrence is rather rare. As for the Chesapeake localities, according to previous records the toadfish lives in the muddy bottoms of the oyster regions of the Chesapeake Bay, around the mouth of the Potomac River, and elsewhere in the saltwater regions. Many specimens were collected from many localities around Annapolis, Maryland to the entrance of the Bay by Hildebrand and Schroeder (1927). Studies on the feeding habits of the toadfish have not been very extensive over the past years as reviewed in the literature. Little attention has been given to very detailed analyses of this type because of their lack of economic importance. (Hildebrand and Schroeder, 1927) in their mention of the toadfish state that its principal food appears to consist of crustaceans, with a combination of mollusks, or other fish. Small crabs among the crustaceans appeared most frequently in the food, although shrimp (and in the smaller individuals Amphipods) and Isopods also were present. Almost any kind of offal is eaten, and in places where garbage is thrown overboard, toadfish are almost always present in comparatively large numbers. (Linton, 1901) noted that the alimentary canal is chiefly filled with crustacean and molluscan remains and the bones and scales of fishes. He also noted finding a partly digested toadfish in the stomach of another. (Gudger, 1908) stated that their favorite food is young molting blue crab; any crustacean will do, however, or fish or almost any kind of offal. This investigation was concerned with the feeding habits of Opsanus tau in the Chesapeake Bay in the vicinity of Crisfield, Maryland. A somewhat detailed analysis was made in the determination of the specific type of food that was present in the comparison to what has previously been noted. In correlation with previous accounts of notations made on the feeding habits of the toadfish , a definite relation occurred between the analyses presented here with earlier findings.
- ItemThe Influence of Calcium on the Distribution of the Ring-Necked Pheasant (Phasianus colchicus) in North America(1954) Dale, Frederick Harold; Littleford, Robert A.; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)
- ItemPLASMA CONCENTRATIONS OF LUTEINIZING HORMONE, FOLLICLE STIMULATING HORMONE AND PROLACTIN IN OVARIECTOMIZED, HYSTERECTOMIZED AND INTACT SWINE(1974) Wilfinger, William Walter Jr; Brinkley, Howard J.; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)In order to critically evaluate the temporal patterns of plasma luteinizing hormone (LH), follicle stimulating hormone (FSH) and prolactin (PRL); blood samples were collected daily at 0600, 1200, 1800 and 2400 hrs from intact, sham, ovariectomized and hysterectomized Yorkshire sows via indwelling vena caval cannulae. The maximum preovulatory plasma LH concentration in the intact and sham operated swine (mean ±l SD, 7.06±2.40 ng/ml) was reached between 2400 hrs on the first day of estrus (day 0) and 0600 hrs on day 1. Preovulatory LH peaks averaged 28.75±4.76 hrs duration from initial rise from, and return to, a baseline concentration of 1.19±.25 ng/ml plasma. In addition to the preovulatory LH peak, an average of 8.75 luteal phase peaks was observed during each estrous cycle . Approximately 69.5% ·of the luteal phase peaks had an average duration of 12.65±1.79 hrs, an average maximum plasma concentration of 2.29±.55 ng/ml and occurred during days 2 to 17. The remaining luteal phase peaks reached a maximum concentration of 2.86±1.04 ng/ml and occurred during days 2 to 13. The average duration of these luteal phase peaks was 18.61± 3.49 hrs. The largest and most consistent plasma FSH peak in the intact and sham operated swine occurred between days 2 and 3. This postovulatory peak had a duration of 58.17±16.25 hrs and reached an average maximum concentration of 13.14±9.42 ng/ml before returning to a baseline of 4.76± 1.56 ng/ml plasma. The initial rise of the postovulatory FSH peak coincided with the initial rise of the preovulatory LH peak, but did not reach maximum concentration until 2.66±.45 days after the preovulatory LH peak had reached maximum concentration. In some animals, a luteal phase FSH peak occurred between days 8 to 14. The luteal phase FSH peaks had a duration of 18.09±5.36 hrs and an average maximum concentration of 9.76± 3.78 ng/ml plasma. An average of 2.58±1.08 plasma PRL peaks was observed between day 0 and day 2 of the estrous cycle in the intact and sham operated swine. These peaks averaged 20.54±4.02 hrs in duration and reached maximum concentrations of 11.49±2.97 ng/ml before returning to a baseline of 6.54± 1.29 ng/ml plasma. They reached their maximum concentration approximately 9.12±9.84 hrs after the maximum concentration of the preovulatory LH peak had been reached. Larger prolactin peaks occurred during the follicular phase of the estrous cycle. An average of 3.09±1.38 peaks occurred between days 14 and 19.· These peaks had an average duration of 18.98±3.30 hrs and reached a maximum concentration of 14.28±4.27 ng/ml plasma. Shortly after removal of the ovaries (6 to 8 hrs), baseline LH (2.2± .14 ng/ml) and FSH (12.20±2.90 ng/ml) plasma concentrations in the ovariectomized swine were significantly greater (P<.05) than those found in the intact and sham operated animals, but baseline prolactin concentrations (6.70±2.10 ng/ml) were not significantly different (P>.05) from the controls. The temporal patterns of maximum plasma concentrations associated with LH (3.47±.21 ng/ml), FSH (21.43±.82 ng/ml) and PRL (9.32±2.00 ng/ml) peaks were not similar among the ovariectomized animals. Baseline LH (1.12±.34 ng/ml), FSH (5.30±2.09 ng/ml) and PRL (6.05± 1.89 ng/ml) concentrations in the hysterectomized swine were not significantly different (P>.05) from the baseline concentrations in the intact and sham operated animals. Numerous plasma LH peaks (14.30±4.59) were observed during the 20-day collection period. These peaks averaged 19.50 ±1.49 hrs in duration and reached maximum concentrations of 2.63±.23 ng/ ml before returning to baseline. Plasma FSH and PRL peaks averaged 21.00 ±4.51 and 17,69±3.50 hrs in duration and reached maximum concentrations of 8.12±1.95 and 10.18±2.95 ng/ml before returning to baseline. Mean plasma LH concentrations in the intact, sham, ovariectomized and hysterectomized swine were significantly greater at the 2400 hr collections than at the 1800 hr collections. A critical assessment of plasma hormone concentrations is an essential prerequisite to a basic understanding of the physiological mechanisms governing the reproductive process. The descriptive data provided by this study will enable future investigators to design critical experiments to evaluate the physiological importance of these hormone fluctuations, thereby broadening our basic understanding of the mechanisms which govern the reproductive cycle.
- ItemThe Significance of Cytological Characteristics as Revealed by Protargol Silver Staining in Evaluating the Systematics of the Ciliate Suborder Tintinnina(1977) Brownlee, David Carl; Small, Eugene B.; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)The present systematics of the tintinnid ciliates is based on the shape, size, and composition of the lorica as established by Kofoid and Campbell. Construction of a classification based on a restricted set of characteristics, such as those pertaining only to the lorica in the tintinnid ciliates, may lead to an artificial or unnatural scheme. This lorica based classification also prohibits phylogenetic comparisons of the tintinnids to other ciliate groups whose taxonomy is based on cytological characteristics. In an attempt to demonstrate the value and necessity of employing cytological characteristics in constructing the taxonomy of the tintinnid ciliates, the cytology of representative species was examined using the protargol silver-impregnation technique. Specimens were collected from a wide range of environments, including marine, brackish, and fresh water habitats which ranged from tropical to temperate latitudes. Eleven species comprising ten genera and representing seven families were chosen to represent the suborder in this preliminary analysis. The examination of the stained species provided the first precise description of somatic ciliation patterns, a more complete understanding of the buccal organization, and insight into the biological processes of these ciliates. Using these observations,comparisons are made to other ciliate groups and a preliminary analysis of evolutionary trends in the tintinnid ciliates is supported. It is suggested that a revision of the placement of certain genera within the families of tintinnids is necessary and that such changes should be based on both cytology and morphology of the lorica.
- ItemDifferences facilitating the coexistence of two sympatric, orb-web spiders, Argiope aurantia Lucas and Argiope trifasciata (Forskal) (Araneidae, Araneae)(1977) Taub, Marilyn Lorraine; Morse, Douglass H.; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)Two closely-related, sympatric, orb-web spiders, Argiope aurantia and Argiope trifasciata, take prey which differ in size. In accordance with the often-assumed direct relationship between the size of predators and their prey, A. aurantia is larger than A. trifasciata at any single point in time, largely a result of their asynchronous reproductive cycles. The ratio of their sizes exceeds the 1.28 proposed by Hutchinson (1959) for coexistence. Vertical and horizontal differences in their use of the microhabitat also occur and may further reduce the overlap in their use of food or reduce the frequency of interspecific interactions. In this study, vertical stratification of webs occurred only late in the season, with A. aurantia higher than A. trifasciata. These results contrast with those of Enders (1974), probably due to different densities of the two species in our study areas. Experiments show that the differences in the size of prey taken by these Argiope spiders were due, in part, to dissimilarities in the filtering properties of their webs and to differences in the ability of the two species to capture prey of the same relative size. However, the differences were mainly due to the spiders' rejection of a large and different portion of the available prey.
- ItemAdenyl Cyclase and Its Relationship to Insect Diapause in the European Corn Borer, Ostrinia Nubilalis (Hubner)(1978) Gelman, Dale Berkman; Lockard, J. David; Hayes, Dora K.; Botany and Science Teaching; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)The purpose of this study was to determine if there is a link between adenyl cyclase activity and the diapause condition in the European corn borer, Ostrinia nubilalis. Insects inhabiting those latitudes where cold and warm seasons alternate with one another have evolved mechanisms which allow them to remain dormant (in a state of diapause) during the winter months of the year. Photoperiod, as well as temperature and humidity, has been shown to control the onset, maintenance and termination of insect diapause. In recent years, evidence supporting a role for the cyclic AMP system, including adenyl cyclase, as well as a role for one or more biogenic amines in the pathway between light reception and the neuroendocrine regulation of the insect life cycle and in the multitude of neuroendocrine pathways controlling insect growth and metamorphosis has been accumulating. In light of this evidence, it was decided to investigate the effects of two light regimens, short day (diapausing-inducing) and long day (pupation-inducing), on adenyl cyclase activity of various stages of fifth instar European corn borer larval heads, and to determine the effects of the biogenic amine neurotransmitters, norepinephrine, octopamine, and dopamine on this activity. Adenyl cyclase activity was measured by a modification of the method of Krishna, et al., (1968). A summary of the results follows. In head extracts of fifth instar European corn borer larvae reared under both long day and short day photoperiodic regimens, adenyl cyclase activity in the presence of sodium fluoride increased as the larvae progressed through early, middle and mature stages. In long day larval heads, activity decreased in late prepupae and reached a low in pharate pupae. In contrast, adenyl cyclase activity in short day larval heads peaked in early diapause and then returned to prediapause levels during late diapause. Norepinephrine significantly enhanced adenyl cyclase activity only in early diapause larval head extracts, while octopamine significantly enhanced adenyl cyclase activity in head extracts of late short day mature and early diapause larvae. Dopamine was ineffective as an activator. An analysis of the combined effect of neurotransmitter and developmental stage revealed that in general, a given neurotransmitter in combination with short day larval head extracts resulted in higher adenyl cyclase levels than that neurotransmitter in combination with long day head extracts.
- ItemResource Partitioning in a Neotropical Necrophagous Scarab Guild(1978) Young, Orrey P.; Morse, Douglass H.; Zoology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)Data collected from naturally occurring and artificially placed vertebrate carcasses were examined for the purpose of revealing mechanisms permitting the coexistence of carrion feeders in tropical forests. Studies concentrated on the necrophagous scarab guild and were conducted at three sites in the Panama Canal Zone during the periods January-June 1974, January-May 1975, and September-December 1975. Only mammalian carcasses were discovered at the principal study site, Barre Colorado Island (BCI). The seven species represented were among the 15 largest mammalian species known to occur on the island. Naturally occurring carcasses were most abundant late in the wet season, but the rate of utilization of carcasses was greatest in the dry season. Vertebrate scavengers appeared to be the most important consumers of carrion on BCI, and were the primary cause of high carcass utilization rates in the dry season. Invertebrate carrion consumers were rare in the dry season, but in the wet season probably consumed as much as 50% of the available vertebrate carrion. Field experiments demonstrated that mammalian carcasses were consumed by arthropods faster than bird carcasses, and that lizard carcasses were consumed very slowly, if at all. Consumption time by arthropods was directly proportional to carcass size, and fresh carcasses attracted many more species of arthropods than did older carcasses. Larval dipterans dominated carrion during the wet season. They could render a typical large (2 kg) vertebrate carcass unsuitable for other consumers in three days and consume 80% of the carcass in nine days. Larval dipterans also provided the food of a large group of predators. Potential competitors of larval dipterans (vertebrates, scarab beetles) were only successful if they arrived at the carcass quickly and removed portions of the carcass before larval dipteran populations rendered the food unsuitable. The necrophagous scarab guild on BCI contained 25 species and partitioned food along several dimensions. Differences in the techniques of removing food from a carcass for subsequent consumption or egg-laying appeared to be the most important in achieving species separation within this guild. Along temporal dimensions, both wet vs. dry season and day vs. night were important in species separation, Also of importance was the ability of species to consume a variety of foods, both carrion and other resources. Body size and trophic apparati were also of some importance. A linear dominance hierarchy, based on fighting ability, exists in the necrophagous scarab guild and is directly correlated with the type of food removal. Species biomass was also directly correlated with the dominance hierarchy. Ball-rolling species, for example, were always capable of taking food away from other species and represented the largest portion of the guild biomass.
- ItemFunctional and Adaptive Significance of Mobbing and Alarm Calls of the Common Crow (Corvus brachyrhynchos)(1983) Brown, Eleanor D.; Schleidt, Wolfgang M.; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)This study is an analysis of the functional and adaptive significance of "caw" calls used by common crows (Corvus brachyrhynchos) in contexts involving danger. Seven tame birds, including three siblings and several birds familiar to the siblings (i.e., within their sight and hearing), were the subjects of playback experiments. Four types of caws associated with danger were played back as test calls: screams, mixed caws, inflected alarm caws, and alert caws. These four test caws were recorded from each of six different individuals (senders) and played back to the experimental subjects (receivers). The vocalizations of the three sibling receivers were tape recorded during playback trials, and three types of response caws were scored: mixed caws, alert caws, and long caws. By counting caws in each 10 s interval during the 1 min before, 20 s during, and 20 s after playback, the following functional interrelationships among cawtypes were found. Mixed caw responses were elicited immediately by, and only by, screams and mixed caws. These caws are used in harassing a predator, and seem to function in part to assemble and coordinate a mobbing group. Alert caw responses were suppressed over the 20 s during which caws were played back for all types of presentations except those of alert caws, but reached a peak just after playback. Alert caws seem to be multifunctional, probably indicating either mildly threatening objects or cessation of danger. Long caw responses were suppressed during the 20 s presentations of all cawtypes, but reached a peak after scream and mixed caw playbacks. Long caws seem to indicate either cessation of danger or continuation of normal activities. By further subdividing numbers of responses on the basis of social familiarity between senders and receivers, the effect of social relationship on responses was examined. The senders were either siblings of, familiar to (heard and seen only from a distance), or unknown to the receivers. The receivers did not respond more to the voices of senders from any particular social category (G goodness-of-fit tests) although the data were not conclusive. The results are discussed in terms of the information encoded in mobbing and alarm calls, the functions of those calls, and the sources of natural selection which may have shaped the evolution of mobbing and alarm vocalizations.
- ItemThe Impact of Planktivory on the Life Histories of Estuarine Crabs(1986) Morgan, Steven G.; Reaka, Marjorie L.; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)Estuarine crabs commonly display two larval dispersal patterns in which larvae are either exported from or retained within estuaries. Explanations for the disparate dispersal patterns are that larvae differ in their susceptibility to predation, which is greater within the estuary than offshore, or in their physiological tolerances to the large temperature and salinity fluctuations of the estuary. Crab larvae which are exported from the estuary survived better in stressful temperature and salinity combinations than those which are retained, and thus the physiological stress hypothesis was rejected. However, exported larvae were more vulnerable to predation by fishes and invertebrates than were retained larvae. The long spines, large body sizes and behavioral responses of retained crab larvae were more effective at deterring predation by two fishes and eleven invertebrates in the laboratory, than were the short spines and small body sizes of exported larvae. Spines generally were more effective against planktivorous fishes than against invertebrates. Spines operated by effectively increasing the size of the larvae and their unpalatability to fishes. Behavioral observations revealed that fishes repeatedly attacked zoeae, but would quickly learn to avoid the noxious prey. The armor of crab larvae enabled them to survive attacks, and fishes repeatedly attempting to swallow long-spined crab larvae frequently would die. Spines did not assist in the flotation or stabilization of crab larvae. Electivities of the three predominant fishes sampled from the Newport River estuary, North Carolina, also were greater for exported than retained species of crab larvae. Predation by larval and juvenile fishes was greater upstream compared to downstream, and greater diurnally than nocturnally. By hatching on nocturnal high tides, larvae rapidly disperse downstream where the probability of predation diminishes. Semiterrestrial crabs hatch on nocturnal spring tides to prevent stranding in tidal creeks. Thus, the hatching rhythms and dispersal patterns of crabs appear to have evolved in concert to transport larvae into coastal waters where the risk of predation is reduced, or to retain larvae within estuaries depending upon the vulnerability of the larva to predation.
- ItemMorphology and neuromuscular properties of chelae of decapod crustacean species from temperate and tropical populations(1986) Blundon, Jay Arthur; Vermeij, Gerrat J.; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)...Both species of decapods showed no seasonal differences in chela muscle performance. Their ability to function over wide ranges of temperatures is undoubtly essential in their successful latitudinal distribution. The difference in the capacity of these two species to rapidly acclimate to cold temperatures is reflected in their natural habitats. C. sapidus lives in estuaries where large short term temperature fluctuations are common. M. mercenaria, a marine coastal subtidal dweller, lives where temperature fluctuations are smaller.
- ItemProbing the Nature of the Voltage-Sensing Mechanism of the Mitochondrial Outer Membrane Channel, VDAC: Initial Kinetic Analysis and Aluminum Chloride-Induced Alterations(1987) Dill, Eleanor Therese; Colombini, Marco; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)VDAC channels are the major permeability pathways through the mitochondrial outer membrane. They exist in a high conducting, "open," state at low potentials and a low conducting, "closed," state at high potentials (>+/- 20mV). The mechanism underlying voltage-dependent behavior is poorly understood. VDAC isolated from Neurospora crassa were studied in planar phospholipid membranes. Aluminum chloride interaction with the protein and analysis of the rates of channel opening and closing were used to probe the mechanism of voltage-dependence. Micromolar amounts of aluminum chloride (>1 uM) decreased the steepness of the voltage-dependence and increased the voltage needed to close half the channels. Open and closed channel conductance levels were essentially unchanged. Neither channel conformation nor ion selectivity were altered. The effective aluminum species is either, or both, aluminate or aluminum hydroxide. The rate constants of channel opening and closing were determined from multi-channel membrane studies. Closure rate constants increased exponentially with increased negative applied voltages, from 0.01/sec at -30 mV to 1.77/sec at -80 mV. Short periods (< 4-6 min) in the open state before closure decreased closure rates, indicating the presence of at least two open states. Opening rates were at least an order of magniture faster than closure rates and had no marked voltage-dependence between -15 mV and -5 mV or +5 mV and +10 mV. Channel closure accounts for 80%, or more, of the voltage-dependence observed in the steady state. Implications of these findings for modeling the action of the channel are discussed. As a result of these studies future models of the VDAC channel and research must consider these new complexities: distinct groups of charges are responsible for voltage-gating and selectivity; the sensor is likely outside the channel proper; channel opening may involve a large dipole; and opening and closing may occur via different molecular pathways.
- ItemBranched Chain Amino Acids: Requirements and Antagonism in the Male Broiler Chick(1987) Farran, Mohamad Talal; Thomas, Owen P.; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)Experiments were conducted to study the effect of feeding the branched-chain amino acids (BCAA), leucine (Leu), isoleucine (Ile) and valine (Val) to 7-21 day old male broiler chicks. Using the central composite rotatable design, the results of response surface regression analysis showed that optimum body weight gain (BWG) and feed conversion values (FC) would be obtained with dietary levels of 1.16, 0.81 and 0.90% for Leu, Ile and Val respectively. Chicks fed a Val deficient diet ad libitum exhibited a ricket-like condition which was characterized by a low Ca content in the bone. The value was 134 as compared to 156 and 172 mg/g dry bone for chicks fed a diet deficient in the three BCAAs and a Val supplemented diet respectively. similar results were obtained when equal amounts of the three diets were given to the birds by using pair feeding and force feeding techniques. Although birds fed the Val deficient diet and those pair fed the BCAA deficient diet had similar BWG, bone measurements (bone ash, dry bone, and bone Ca) were significantly lower (p < 0.05) for the Val deficient group. Serum ca (mg/dl) was not significantly different. Excretion of urinary ca, however, was enhanced by feeding a Val deficient diet as compared to the Val supplemented treatment suggesting that a proper ratio of the BCAAs may be required to form the bone matrix which serves as a base for mineral deposition. Feeding a Val deficient diet significantly (p < 0.05) lowered the protein content of the feathers. The value was 82.7% as compared to 85.0 and 88.0% for all BCAA deficient and Val supplemented diets respectively. Valine deficiency also changed the pattern of feather amino acids by increasing the levels of aspartic acid, glutamic acid, methionine, tyrosine, histidine and lysine. Cysteine level, however, was decreased. High dietary Leu(≥ 3.0%) depressed BWG and FC of ad libitum fed birds. When Ile and Val were simultaneously added to the diet the growth rate and FC were similar to the controls. The ketogenic property of Leu was tested by measuring β-OH-butyrate level in the plasma (mg/1) and found to be nonsignificant.
- ItemProduction and energetics of Atlantic menhaden in Chesapeake Bay(1993) Rippetoe, Thomas Hunt; Brandt, Stephen B.; Marine-Estuarine-Environmental Sciences Program; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)Laboratory experiments were conducted to examine the effects of temperature and prey type on maximum consumption, absorption efficiency and gastric evacuation rates of age 0 Atlantic menhaden Brevoortia tyrannus. Maximum consumption reached a peak or asymptote between 25 and 29°C. Temperature had no effect on absorption efficiency, but gastric evacuations rates increased with increasing temperatures. Artemia sp. nauplii were absorbed more efficiently than the diatom Ditylum brightwelli. Prey type had no effect on gastric evacuation rates at temperatures below 25°C but D. brightwelli was evacuated faster than Artemia sp. nauplii at 28°C. Field estimates of daily ration based on stomach content analyses for age 0 menhaden were 5.5% of dry body weight (3.6% wet weight) in June and 3.6% of dry body weight (3.0% wet weight) in August. Most prey in menhaden stomachs were dinoflagellates, diatoms and a mixture of amorphic phytoplankton and detritus. Less than 1% of total biomass in menhaden stomachs was copepods. A diurnal feeding periodicity was apparent with peaks in stomach contents occurring around dusk. A bioenergetics model was developed for age 0 menhaden in mid-Chesapeake Bay. The model incorporated temperature and weight-specific parameters for consumption and respiration and site-specific parameters for growth, diet, energy density of predator and prey and water temperatures. Model estimates of population consumption and production were sensitive to assumptions about annual mortality rates. Daily population consumption peaked in September which coincided with the second annual peak in primary productivity typical of mid-Chesapeake Bay. Daily production peaked from mid-August through September. Model results showed that in 1990 menhaden population consumption would have removed <5% of primary production in mid-Chesapeake Bay from June through October.
- ItemBEHAVIORAL ECOLOGY OF JUVENILE PALILA (Loxioides bailleui): FORAGING DEVELOPMENT, SOCIAL DYNAMICS, AND HELPING BEHAVIOR(1998) Miller, Linda Joyce; Gill, Douglas E.; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)The purpose of this study was to systematically document helping development of foraging in juvenile Palila, an endangered Hawaiian honeycreeper found only on Mauna Kea on the island of Hawaii. Though incidental observations of helpers-at-the-nest have been made, intensive nest monitoring revealed that 30 to 50% of nests had one extra after-second-year male provisioning food to the nestling(s). Helping at the fledgling stage was also confirmed. Radiotracking revealed information regarding foraging development and movement patterns of juveniles. Adult males provided one-on-one food supplementation and foraging instruction to young for three to four months after fledging. Particular benchmarks in the development of foraging skills in juveniles were identified. Juvenile survival may be a factor limiting the Palila population. This investigation constitutes the first detailed study of a juvenile Hawaiian forest bird, and thus, may serve as model for understanding the ecology of other species.
- ItemUnderstanding Maternal Effects as a Recruitment Mechanism in Lake Michigan Yellow Perch (Perca flavescens)(2000) Heyer, Christopher James; Miller, Thomas J.; Biology; Marine - Estuarine - Environmental Sciences Program; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)Changes that have occurred in the abundance and trait distribution of adult Lake Michigan yellow perch (Perca flavescens) suggest that maternal effects on larval traits may be substantially influencing the recruitment of this heavily exploited species. Maternal effects on yellow perch larvae at hatching and through 32 days post hatch (dph) were investigated in ten maternal lines to test the null hypotheses of no effect of maternal condition on offspring condition at hatching, no persistence of maternal effects under conditions of starvation and high food availability, and no difference in offspring survival under conditions of starvation and high food availability. Maternal effects were detectable at hatching and likely result in differences among females in size, age, gonadal somatic index, and egg production. Maternal effects at hatching were expressed by differences in larval total length, yolk volume, dry weight, and DNA quantity. Maternal effects persisted under conditions of starvation to 6 dph, after which point virtually all larvae had perished. Maternal effects resulted in a twofold difference in resistance to starvation among the maternal lines. Larvae that exhibited the lowest resistance to starvation were long with small yolk volumes, while those exhibiting the highest resistance to starvation were short with large yolk volumes. Under high food availability maternal effects persisted to 32 dph, and resulted in threefold differences in survival among the maternal lines. No clear mechanism was identified to account for these survival differences. The observed maternal effects in Lake Michigan yellow perch may have substantial implications on recruitment.
- ItemInterannual and Regional Patterns of Abundance, Growth, and Feeding Ecology of Larval Bay Anchovy (Anchoa Mitchilli) in Chesapeake Bay(2003) Auth, Toby D.; Houde, Edward D.; Marine Estaurine and Environmental Science Program; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)Patterns in abundance, growth , and feeding by larval bay anchovy were examined in Chesapeake Bay from 1995-1999 to evaluate factors that contribute to variable recruitments of this abundant fish. The patterns were examined in relation to environmental factors, including hydrography and distributions of prey (zooplankton) and a probable predator (ctenophore). Larval abundances, sizes, feeding incidences, and growth rates varied annually and regionally. Averaged over five years, mean abundances in July decreased by almost two orders of magnitude from the mouth (38.l/m2) to the head (0.6/m) of the Bay, a long a declining salinity gradient. Yearly survey, bay-wide mean abundance varied nearly 10-fold; it was highest in 1998 (42. 7 /m2) and lowest in 1996 (4.6/m2). Feeding incidence was highest in 1998 (23%) and lowest in 1996 (9%), and varied regionally from 27% in the upper Bay to 13% in the mid Bay. Larvae fed predominantly during daylight. The most common prey ingested were copepod eggs and various life stages of calanoid copepods (primarily Acarlia Lonsa). Growth rates of larvae also differed annually and regionally. Mean growth rate was highest in 1998 (0.81 mm/d) and lowest in 1999 (0.68 mm/d), and varied regionally from 0.83 mm/d in the upper Bay to 0.71 mm/din the mid Bay. Zooplankton concentration was positively correlated with larval feeding incidence (r = +0.66) and growth rate (r = +0. 72). Larval feeding incidence was strongly correlated (r = +0.93) and summer larval abundance significantly correlated (r = +0.86) with fall recruitment of young-of-the-year bay anchovy.
- ItemRemoval of Wastewater Nitrogen and Phosphorus by an Oligohaline Marsh(2003-10-15) Traband, Jason John; Fisher, Thomas R; Cornwell, Jeffery C; Stevenson, J C; Stribling, Judith M; Marine-Estuarine-Environmental SciencesWetlands potentially contribute to water quality improvement. The objective of this thesis was to determine the role of wastewater processing by oligohaline Council Creek marsh (0.16 km2), which receives wastewater from Easton, MD. Tidal flushing, nutrient distributions, plant uptake, and sediment burial were examined as removal mechanisms. This marsh seems to be little affected by, and has a small impact on wastewater. Wastewater flow can raise mean water levels by 3 cm in addition to seasonal changes of 30 cm induced by thermal expansion and contraction of seawater. During the ~3 d flushing time of water, nutrients passing through the marsh experienced small transformations compared with 2575% dilution of wastewater in the marsh by Choptank River water, during summer high sea level stands. During the growing season, marsh plants intercepted 3044% N and 1117% P, while sediment burial appeared to remove 27% N and 6% P, annually.
- ItemThe Effects of Spraying Deltamethrin Against Tsetse Flies on Insectivorous Birds in the Okavango Delta, Botswana(2003-10-22) Pendleton, Frank N; Baldwin, Andrew H; Marine-Estuarine-Environmental SciencesI investigated the effects of spraying deltamethrin for tsetse fly control on bird populations in the Okavango Delta, Botswana. Because deltamethrin has low toxicity to vertebrates, effects on birds would have been indirect and caused by reductions in insect food supplies, not by poisoning. The northern half of the Delta was sprayed in 2001 and the southern half in 2002. I monitored resident bird populations at four sites (two in each spray block), using point counts. Birds were classified by diet as insectivorous or non-insect-dependent in order to check for declines in insectivorous. Sections of the 2002 spray block burned before the spraying started. In the 2001 spray block, there were no declines of insectivorous birds, and varied results for non-insect-dependent birds. In the 2002 spray block, the Chitabe site showed declines in insectivorous forest birds, which were not strongly correlated with the spraying, and Nxaraxa showed no such declines.
- ItemBioaccumulation of Polychlorinated Biphenyls in the Delaware River Estuary(2003-11-03) Toaspern, Megan; Baker, Joel E; Secor, David H; Rowe, Chris; Marine-Estuarine-Environmental SciencesComposite collections of channel catfish (Ictalurus punctatus), white perch (Morone americana), their prey items (forage fish and epibenthos), and surficial sediment were collected in the Delaware River estuary in Fall 2001 and Spring 2002 to quantify polychlorinated biphenyl (PCB) accumulation and to examine the mechanisms of bioaccumulation and trophic transfer. Samples were collected from four zones in a section of the Delaware River from Trenton, NJ to Liston Point, DE, and analyzed for lipid content and the hydrophobic organic contaminants PCBs. Our results indicate PCB levels and congener distributions in biota reflect spatial and temporal trends in ambient PCB concentrations. PCB congener patterns vary among sampling zones, with higher homologue groups enriched in lower zones. Demersal species have similar congener accumulation patterns. The presence of highly chlorinated congeners in lower zones does not reflect commercial Aroclor mixtures, indicating a possible point source of PCB contamination in the region downstream of Philadelphia, Pennsylvania. The relationships between total PCB levels in biota and those in water and sediment was constant over the study area based on bioaccumulation parameters. Ambient water quality criteria calculated for the Delaware River with estuarine-specific values derived from this study indicates a major reduction in PCB point and non-point loadings is necessary to reduce PCB contamination in fish, thereby meeting acceptable risk levels for human consumption.