DISCUSSION
The present study indicates that from habitat size expressed as area, and the particular environment in
which they are found, we can roughly predict the species
of mosquito immatures that occur and how they
encounter aquatic predators. In relation to habitat size,
the 6 major mosquitoes in the present study can be
divided into 3 groups.
The first group consists of Ae. (Stegomyia) spp.
and T. bambusa which occurred mostly in small
containers. Ae. japonicus and Cx. kyotoensis can be
placed in the second group. They occurred frequently
in larger containers compared to the first group, but
rarely occurred in containers of more than 1 m2
, and
never occurred in rice fields. The third group includes
An. sinensis and Cx. tritaeniorhynchus, which occurred
in rice fields in summer and colonized large containers
after water was drained from rice fields.
Occurrence patterns in relation to container size
can be determined by (1) habitat preference by adult
females and (2) mortality of ovipositing females or their
immature offspring. Mortality causes, either abiotic or
biotic such as predation and competition, are
probabilistic processes that depend on the condition
of each container. For example, in containers where no
predators had colonized, by chance, predation cannot
be a factor determining mosquito fauna. Therefore it is
unlikely that mortality alone limits range in habitat size
very clearly.
The 3 groups of mosquitoes showed clear
differences in occurrence patterns in relation to habitat
size. The upper limit of habitat size for the first group
and the lower limit for the third group are probably
determined primarily by stereotypic habitat preference
by each species. Several chemical and physical cues
are involved in oviposition behavior of mosquitoes
(Bentley and Day 1989). It is not clear whether the
mosquitoes in the present study can recognize the size
of containers as visual information, or whether they
react to some other physico-chemical cues that are
related to container size. Washburn (1995) referred to
MacArthur and Wilson’s (1969) island biogeography
theory to explain the richer fauna in pools than in
containers. However, because their theory assumed
equal colonization rates for all species, it cannot be
applied directly to the cases in which each species prefer
certain habitat size.
Compared with the occurrence patterns of
mosquitoes that varied among species, those of
predators seemed to be more uniform. The five major
predators, Cx. halifaxii, Notonectidae, Anisoptera,
Chaoborus sp. and Veliidae occurred more frequently
in large containers. Except for Chaoborus sp., they
were also collected from rice fields. It is reasonable to
assume that predators did not occur in small containers
because smaller containers may produce smaller
amount of prey, either when the food webs in containers
are based on autotrophic algae or heterotrohic
microorganisms that decompose leaf litter and other
detritus as carbon sources. The containers smaller than
0.01 m2
, in which predators rarely occurred, might be
too small to support trophic levels higher than filterfeeding
mosquitoes in this region. As another factor
that is related to container size, habitat persistence
might be important for some predators, because small
shallow containers in open sites frequently dry up.
However, the drought is probably not an important
limiting factor in the use of small containers by
predators in this study because they also occur in rice
fields that dry several times during the rice-cultivating
period (June - September).
Predators occurred more frequently in larger
containers, and opportunity for predation should be
smallest in the first group. Actually, Ae. (Stegomyia)
spp. and T. bambusa rarely or never co-occurred with
predators. Although some predators, such as
Toxorhynchites mosquito larvae (Bradshaw and
Holzapfel 1983, Sota and Mogi 1996) or damselfly
nymphs (Fincke 1994), have adapted to container
habitats in some regions, many other predators including
those in the present study seem not to be capable of
colonizing small containers. Apparently, mosquitoes
such as Ae. (Stegomyia) spp. and T. bambusa can escape
from habitat-generalist predators by preferring small
containers as breeding sites. Once they have escaped,
predation is no longer an important factor in regulating
their populations. Instead, intra- and interspecific
competition for food might be severe, as several studies
have indicated for container mosquitoes (Mori and Wada
1978, Carpenter 1983, Bradshaw and Holzapfel 1992,
Leonard and Juliano 1995, Sunahara and Mogi 1997a,
b). In relatively persistent aquatic sites with limited
resources, such as deep bamboo stumps, T. bambusa
is competitively superior to Ae. albopictus, although
the latter can use temporary habitats more effectively
than the former (Sunahara and Mogi 1997b). In this
region, much rainfall is observed in the summer and
many temporary small-container habitats appear in this
season. Succes
DISCUSSIONThe present study indicates that from habitat size expressed as area, and the particular environment inwhich they are found, we can roughly predict the speciesof mosquito immatures that occur and how theyencounter aquatic predators. In relation to habitat size,the 6 major mosquitoes in the present study can bedivided into 3 groups.The first group consists of Ae. (Stegomyia) spp.and T. bambusa which occurred mostly in smallcontainers. Ae. japonicus and Cx. kyotoensis can beplaced in the second group. They occurred frequentlyin larger containers compared to the first group, butrarely occurred in containers of more than 1 m2, andnever occurred in rice fields. The third group includesAn. sinensis and Cx. tritaeniorhynchus, which occurredin rice fields in summer and colonized large containersafter water was drained from rice fields.Occurrence patterns in relation to container sizecan be determined by (1) habitat preference by adultfemales and (2) mortality of ovipositing females or theirimmature offspring. Mortality causes, either abiotic orbiotic such as predation and competition, areprobabilistic processes that depend on the conditionof each container. For example, in containers where nopredators had colonized, by chance, predation cannotbe a factor determining mosquito fauna. Therefore it isunlikely that mortality alone limits range in habitat sizevery clearly.The 3 groups of mosquitoes showed cleardifferences in occurrence patterns in relation to habitatsize. The upper limit of habitat size for the first groupand the lower limit for the third group are probablydetermined primarily by stereotypic habitat preferenceby each species. Several chemical and physical cuesare involved in oviposition behavior of mosquitoes(Bentley and Day 1989). It is not clear whether themosquitoes in the present study can recognize the sizeof containers as visual information, or whether theyreact to some other physico-chemical cues that arerelated to container size. Washburn (1995) referred toMacArthur and Wilson’s (1969) island biogeographytheory to explain the richer fauna in pools than incontainers. However, because their theory assumedequal colonization rates for all species, it cannot beapplied directly to the cases in which each species prefercertain habitat size.Compared with the occurrence patterns ofmosquitoes that varied among species, those ofpredators seemed to be more uniform. The five majorpredators, Cx. halifaxii, Notonectidae, Anisoptera,Chaoborus sp. and Veliidae occurred more frequentlyin large containers. Except for Chaoborus sp., theywere also collected from rice fields. It is reasonable toassume that predators did not occur in small containersbecause smaller containers may produce smalleramount of prey, either when the food webs in containersare based on autotrophic algae or heterotrohicจุลินทรีย์สลายใบไม้และอื่น ๆเศษซากเป็นแหล่งคาร์บอน ภาชนะบรรจุขนาดเล็กกว่า0.01 m2ล่าซึ่งไม่ค่อยเกิด อาจจะเล็กเกินไปสนับสนุนระดับชั้นอาหารสูงกว่า filterfeedingยุงในภูมิภาคนี้ เป็นอีกหนึ่งปัจจัยที่เกี่ยวข้องกับขนาดภาชนะ ที่อยู่อาศัยอยู่อาจไม่สำคัญสำหรับบางล่า เนื่องจากขนาดเล็กช้อปปิ้งในไซต์ที่เปิดบ่อยแห้งขึ้นอย่างไรก็ตาม ฤดูแล้งไม่น่าจะมีความสำคัญปัจจัยจำกัดในการใช้ภาชนะบรรจุขนาดเล็กโดยล่าในการศึกษานี้ เพราะพวกเขาเกิดขึ้นในข้าวฟิลด์ที่แห้งหลายครั้งในระหว่างการเพาะปลูกข้าวระยะเวลา (มิถุนายน - กันยายน)ล่าเกิดขึ้นบ่อยครั้งในขนาดใหญ่ภาชนะบรรจุ และโอกาสปล้นสะดมควรเล็กที่สุดในกลุ่มแรก จริง Ae (Stegomyia)ออกซิเจนและ T. ขยายพันธุ์ไม่ค่อย หรือไม่เคยร่วมเกิดด้วยนักล่า แม้ว่าล่าบาง เช่นตัวอ่อนของยุง Toxorhynchites (Bradshaw และHolzapfel 1983, Sota และ Mogi 1996) หรือ damselflyมีการดัดแปลงมาเป็นนิมพ์ (Fincke 1994), คอนเทนเนอร์ที่อยู่อาศัยในบางภูมิภาค ล่าอื่น ๆ รวมทั้งหลายในการศึกษาดูเหมือนไม่สามารถอาณานิคมภาชนะขนาดเล็ก เห็นได้ชัด ยุงเช่น Ae ออกซิเจน (Stegomyia) และขยายพันธุ์ T. สามารถหลบหนีจากคนที่อยู่อาศัยล่าโดยคุณเล็กภาชนะเป็นพันธุ์ไซต์ เมื่อพวกเขาได้หลบหนีปล้นสะดมไม่เป็นปัจจัยสำคัญในการควบคุมประชากรของพวกเขา แทน intra - และ interspecificการแข่งขันอาหารอาจรุนแรง เป็นหลายการศึกษาระบุสำหรับคอนเทนเนอร์ยุง (โมริและ Wada1978 ช่าง 1983, Bradshaw และ Holzapfel 1992เลียวนาร์ด และผู้ใช้ 1995, Sunahara และ Mogi 1997aข) ในเว็บไซต์น้ำปัจจุบันค่อนข้างมีจำกัดทรัพยากร เช่นตอไม้ไผ่ลึก T. ขยายพันธุ์จะสามารถแข่งขันได้ดีกว่า Ae albopictus แม้ว่าหลังสามารถใช้แหล่งที่อยู่อาศัยชั่วคราวได้อย่างมีประสิทธิภาพกว่าในอดีต (Sunahara และ Mogi 1997b) ในที่นี้ภูมิภาค สังเกตปริมาณน้ำฝนมากในฤดูร้อน และอยู่อาศัยขนาดเล็กภาชนะชั่วคราวจำนวนมากที่ปรากฏในนี้ฤดูกาลนี้ สำเร็จจริง ๆ
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