Fluctuations In Relative Abundance Research Articles

Distribution and Feeding Habits of Two Surgeonfish, Zebrasoma xanthurum and Ctenochaetus striatus in the Gulf of Aqaba, Red Sea

.The distribution and feeding habits of Zebrasoma xanthurum (Blyth, 1852) and Ctenochaetus striatus(Quoy and Gaimard, 1824) have been studied fora period of 13 months on the coral reefs at Naama Bay, Gulf of Aqaba, Red Sea. Z. xanthurum was a grazer whereas C. striatuswas a detritus feeder. Dentition and alimentary tracts reflected on the food habits of . each species. The feeding rate in Z. xanthurum was higher than in C. striatus; however, both species exhibited definite daily patterns. Feeding was very lowin the morning, peaks in late afternoon and drops sharply as night approaches. The amount of food in the stomach was very low, however, the food weight in the whole gut reaches up to 30% offish body weight daily. In Z. xanthurum, brown algae were the main food items (44.4%), followed by red algae (26.4%), blue green algae (18.2%), green algae (4.7%) and diatoms (2.4%). Animal food contributed only 2.1% of the diet. In C. striatus, substrates (sand and fragments of dead corals) were the most abundant (58.6%) component in the stomach, followed by diatoms (8.6%), red algae (7.6%), brown algae (6.7%) and blue-green algae (5.6%). AnimaIfoods constituted 10.3% of diet and included foraminifera (3.6%), sponges (2%), coelentrates (1.4%) and fish eggs (1.6%). The different food items in both species exhibited seasonal fluctuations in relative abundance. تشمل هذه الدراسة بيئة الغذاء والتغذي لأسماك زبراسوما زانتثوريوم وكيتنوكاتس ستراياتس لمدة تزيد عن عام في منطقة الشعاب المرجانية الواقعة في خليج نعمة ـ جنوب خليج العقبة ـ البحر الأحمر . أظهرت الدراسة الحقلية أن نشاط التغذي في كلا النوعين يستمر طوال النهار ولكن معدل التغذي يتزايد تدريجيا من فترة الشروق ويصل إلى أقصاه بعد الظهيرة. وأوضحت الفحوصات المعملية أن طبيعة الغذاء وطريقة الحصول عليه تعكس التغيرات في تراكيب القناة الهضمية لكلا النوعين حيث وجد أن زبراسوما زانثوريوم تتغذى أساسا على الطحالب التي تمثل 95% من كمية المحتوى الغذائي وتأتي الطحالب البنية في المقدمة 44.4%) تليها الطحالب الحمراء (26.4%) فالخضراء المزرقة (18.2%) فالخضراء (4.7%) وأخيرا الدياتومات 2.4%) . أما المكونات الحيوانية الممثلة بأنواع كثيرة من اللافقاريات فلا تتجاوز 2.1% من كمية المحتوى الغذائي. وتتغذى أفراد كيتنوكاتس ستراياتس على المواد شبه الدبالية حيث تمثل الرواسب المكونة أساسا من بقايا الشعاب المرجانية 58.6% يليها الدياتومات ( 8.6%) ثم الطحالب الحمراء ( 7.6%) والبنية ( 6.7%) والخضراء المزرقة(5.6%) والخضراء (3%) . والجدير بالذكر أن المكونات الحيوانية تمثل 10.3% من كمية المحتوى الغذائي. وهكذا فإنه بالرغم من أن كل من النوعين من الأسماك يقطنان نفس البيئة إلا أن هناك اختلافات معنوية في نسبة الأنواع المختلفة من مكونات المحتوى الغذائي وخاصة الطحالب التي تتأثر باختلاف المواسم .

Ecosystem dynamics through the past 2000 years as revealed by fossil mammals from Lamar cave in Yellowstone National Park, USA

Lamar Cave, a late Holocene paleontological site in Yellowstone National Park, USA, has yielded 36 fossil mammal species from 10 stratigraphic units representing about 2000 years. The fossil fauna is similar to the mammals in the park today and affords a unique opportunity to investigate paleocommunity and ecosystem dynamics through time. Remains of an extralimital species in Yellowstone today, Microtus ochrogaster are found only in the oldest cave deposits, dated at 1695 ± 60 yr B.P. Disappearance of this species by about 1550 years ago marks evolution into the ecosystem that has persisted into the present and is recognizable by a fossil mammal assemblage that is virtually identical to the modern one. Relative abundance fluctuations in the mammal populations imply community resilience through the past 2000 years. Trends in relative abundances of small mammals, particularly the inverse relationship between Microtus and Spermophilus are interpreted as evidence of declining grass cover near Lamar Cave betwe...

High resolution biochronology in the Monte Narbone Formation of the Capo Rossello section and the Mediterranean first occurrence of Globorotalia truncatulinoides

Quantitative analysis on the planktonic foraminiferal assemblages in the Late Pliocene - Early Pleistocene segment of the Capo Rossello section evidences the same number of relative abundance fluctuations of the Globigerinoides ruber taxonomic unit recorded in the same stratigraphic interval of other Mediterranean sequences. Between the Globorotalia inflata FO and the Discoaster brouweri LO 4 relative abundance fluctuations are present. Since the D. brouweri LO is recorded in the Mediterranean basin below the base of the Olduvai magnetic event and in coincidence of relative abundance fluctuation 73, the Gt. inflata FO is coincident with fluctuation 80. The first appearance ol Globorotalia truncatulinoides is recorded on the second fluctuation above the Gt . inflata FO and on the second fluctuation below the D. brouwueri LO. Therefore the Gt. truncatulinoides FO is coincident with fluctuation 77. The absolute age proposed for these 3 bio-events is 1.99,2.07 and 2.13 MA respectively. The most important calcareous nannofossil events, recognized by quantitative analysis, have been correlated to the abundance fluctuations of the Globigerinoides ruber taxonomic unit.

Pliocene-Early Pleistocene astronomically forced planktonic Foraminifera abundance fluctuations and chronology of Mediterranean calcareous plankton bio-events

The absolute age estimates for calcareous plankton events proposed by the writer in a recent paper are discussed according to the new proposed paleomagnetic time scales. A re-interpretation of the sequence of lithological cycles recognized in the composite makes their number perfectly comparable with the number of planktonic foraminifera abundance fluctuations in the same stratigraphic interval. An absolute age of 5.33 MA is estimated for the base of the Pliocene, as defined in the Capo Rossello section. Periodicity of the relative abundance fluctuations of the planktonic foraminiferal assemblages during the Early Pleistocene stratigraphic interval is estimated at about 41 kyr, well comparable with the periodicity of the obliquiry astronomical cycles. By correlation of the sequence of biostratigraphic events recorded in the Early Pleistocene interval in the Mediterranean sections with the sequence of abundance fluctuations, their absolute ages have been obtained, as well as the absolute age of chronostratigraphic boundaries. The base of the Pleistocene is at 1.83 MA and the top of the Early Pleistocene, coincident with the top of the Sicilian, is at 0.89 MA. A re-evaluation of the Oxygen isotopic Stages of the upper Singa section is proposed, on the base of paleomagnetic and calcareous plankton biostratigraphic data reported for this section. Correlation with the North Atlantic Site 607 proved that rhe G. oceanica s.l. FO, the C. macintyrei LO and rhe Gephyrocapsa sp.3 FO are slightly diachronous between the Mediterranean and the mid-North Atlantic high latitudes.

Ovitrap surveys of dengue vector mosquitoes in Chiang Mai, northern Thailand: seasonal shifts in relative abundance of Aedes albopictus and Ae. aegypti.

Aedes aegypti (L.) and Aedes albopictus (Skuse) were surveyed using ovitraps in residential areas in Chiang Mai, northern Thailand. Egg populations (both species inclusive) remained low in the dry season, but increased/decreased exponentially during the first/latter half of the rainy season, respectively. This seasonal pattern was similar to the seasonal distribution of dengue haemorrhagic fever cases in the area. During the dry season (November-March) Ae.aegypti was dominant in urban and indoor ovitraps. With onset of the rainy season in April, relative abundance of Ae.albopictus increased in rural and outdoor ovitraps. Ae.albopictus displaced Ae.aegypti in the latter half of the rainy season in the rural area. Possible mechanisms to account for this seasonal decline of Ae.aegypti and reciprocal fluctuations in relative abundance of Ae.albopictus are discussed in relation to food availability for larvae in container habitats.