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Tuesday 15 March 2016

Relevansi Teori Perkembangan Populasi Tehadap Pendugaan Populasi Hama



Penyebaran spesies, perubahan dan evolusi merupakan fitur ekologi dan memang mempengaruhi aspek dinamika populasi. Jadi toleransi biologis dari hama tidak dapat sepenuhnya dipisahkan dari dinamika penduduk. Tingkat kesulitan atau disbenefit spesies yang akan memberikan status hama tergantung pada;
a.       Jumlah organisme yang ada.
b.      sensitivitas atau toleransi dari korban (tanaman, hewan, orang) ke serangan hama ini.
Toleransi ini terdiri dari faktor-faktor sosial ekonomi (mis. toleransi pasar) ditinjau oleh Norton & Conway (197). Variasi genetik dalam hama memberikan kontribusi penting perbedaan toleransi biologis. Dalam hubungan host baru toleransi biologis sering rendah ini dalam kaitannya dengan penyakit. Dalam kasus di mana hubungan tanaman serangga dan host baru yang dibentuk tanaman, sering tampak sangat rentan terhadap kerusakan.
Perekrutan, migrasi dan tingkat kematian yang rendah, ada sedikit paparan habitat baru dan kesempatan lebih sedikit untuk penyesuaian
perubahan lingkungan. Organisme ini khusus untuk lingkungan khusus mereka dan jika jumlah mereka berkurang ke tingkat yang rendah seperti r-strategi, mereka mungkin punah.
Pada tingkat tropik lain banyak lalat yang r-organisme: rumah (musca) atau daging (sarcophaga) lalat di bahan membusuk, Agas mycetophilid di tubuh buah jamur dan drosophilids tertentu dalam buah berdaging dan dengan habitat skala yang lebih besar, begitu juga belalang dan ulat grayak (Spodoptera exempta). Di antara tanaman benar r-strategi yang diwakili oleh ruderals berumur pendek, seperti prinsip asasi (vulgaris Senecio) yang memproduksi sekitar saya, propagul ooo dengan waktu generasi sering sedikit lebih dari lima minggu (sasilsburry 1961).
Uvarov (1957) menunjukkan bagaimana pengelolaan, terutama penggembalaan, dari banyak daerah kering telah sangat meningkat tempat berkembang biak cocok untuk belalang. Banyak wadah buatan terkait dengan perpindahan sangat meningkatkan situs perkembangbiakan beberapa nyamuk, seperti aegepti aedes. Populasi tinggi Australia telah meningkat tajam sisi perkembangbiakan dari bushfly (Musca vetustissima); serangga yang recolonizes banyak jangkauan per tahun (Hughes 1970, Hughes & walker 1970).
Salah satu fitur yang paling karakteristik dari r-strategi kecenderungan migrasi mereka tinggi, penting untuk gerakan mereka dari 'sekarat habitat' ke salah satu yang baru. Seperti disebutkan di atas populasi mereka karena secara teratur membangun di salah satu habitat dari rendah ke tingkat tinggi; mereka eksogen atau imigran hama untuk tanaman tertentu. Karena sifat fana dari pewaris habitat lokal ini sering berguna untuk menipu populasi mereka pada skala regional (Mackauer & Way 1976). Harus ditekankan bahwa pada skala ini proporsi yang sangat tinggi dari total kematian akan padat-bebas terkait dengan migrasi, meskipun tingkat migrasi itu sendiri mungkin kepadatan terkait. Ketika populasi daerah dianggap sering jelas bahwa ada tingkat rendah, mewakili kepadatan ekologi, di musim-musim tertentu. Tingkat rendah (palung), sering terjadi pada tanaman liar seperti itu tidak penting ekonomi langsung, telah diabaikan yang sangat disayangkan karena kemacetan seperti ini peluang kontrol potensial. Beberapa r-hama, yang menuju awal jurang musuh alami pada model, menunjukkan fenomena ini: Aphis fabae lebih musim dingin pada poros (Way & Perbankan 1968 & Cammell 1973) dan frit terbang dari rumput liar (Southwood & Jepson 1962 ), banyak heteroptera (misalnya e.g Dysdercus, Acanthomia) di estern dan Afrika selatan melewati musim kering di sejumlah host liar.

Hama menengah
Organisme ini berada di area jurang musuh alami dalam model. Mereka berkisar dari spesies di r-end, seperti kutu daun sereal untuk spesies di K-end seperti bullfinch dan lain-lain yang dibahas dalam sextion berikutnya. Fitur yang dominan dari dinamika populasi mereka adalah bahwa mereka umumnya diadakan di tingkat yang lebih rendah daripada daya dukung habitat mereka oleh aksi musuh alami. Respon numerik meningkatkan sebagai salah satu bergerak sepanjang musuh alami. Respon numerik meningkatkan sebagai salah satu bergerak sepanjang lembah ke K-end: ini adalah karena meningkatnya stabilitas durasi habitat memberikan lebih banyak waktu untuk respon ini dan dengan demikian menggaris bawahi peran waktu sebagai sumber daya (Watt 1971). Kadang organisme akan menjadi epidemi dalam situasi alami karena kebisingan lingkungan, seperti penyimpangan iklim, akan mengubah hubungan cukup untuk populasi untuk lulus rilis atau melarikan diri (Voute 1946) titik. Frekuensi yang ini akan terjadi akan tergantung pada tingkat kebisingan lingkungan dan lebar jurang (Southwood & Comins 1976).
Jadi berbeda dengan ekstrim r-strategi yang secara alami hama hampir sepanjang waktu, spesies peralihan akan Arsip status OPT, dalam situasi alami, hanya kadang-kadang. Perubahan populasi dinamika yang terjadi sebagai salah satu bergerak maju di seluruh lanskap, di sepanjang jurang musuh alami, dapat dijelaskan dengan mengacu kutu daun. Kutu daun suhu sereal merupakan kondisi dekat dengan r-akhir spektrum: studi dari Potts (1977) (juga ditinjau oleh Southwood & Comins 1976) menunjukkan pentingnya predator umum autochtonous dalam mencegah wabah, dalam memegang populasi tingkat yang sangat rendah. Jika kutu daun melarikan diri dari kontrol ini angka mereka biasanya akan naik ke kepadatan tinggi (Hagen & van den Bosch 1968). Seperti di banyak situasi di tanaman subur spesifik alami musuh, coccinellids, syrphids, chrysopids, sem terutama efektif bila penduduk sudah, barang yang model sinoptik, di 'kecelakaan lembah' (Van Emden et al. 1969, Mackauer & Way 1976). Kontras disediakan oleh alphid tropis Toxoptera Aurantii kakao: habitat stabilitas durasi yang lebih besar dan karenanya lebih jauh dari r-end dari kutu daun sereal. Spesies ini, yang hadir dalam koloni sering kecil di bawah daun kakao tetapi sebagai aturan 'menyebabkan kerusakan kecil' (Entwistle 1972), dipelajari oleh Firempong & Kumar (1975). Mereka menemukan musuh alami tertentu, terutama coccinellids dan syrphids, efektif, sering menyerang koloni segera setelah pembentukan. Namun beberapa kutu daun bertahan hidup terutama ketika larva syrphid adalah predator. dalam ringkasan perbandingan ini menunjukkan probabilitas yang lebih besar dari wabah di tanaman subur, tapi (non-wabah) kepadatan penduduk endemik tinggi dalam tanaman pohon.

Strategi pengendalian hama
Ahli biologi terapan telah mengakui bahwa karakter habitat merupakan indikator penting bagi strategi managemen hama (Southwood & Way 1970) dan Conway (1976) menunjukkan bahwa sebagai kontinum rk terkait dengan habitat karakteristik relevan dengan keputusan pada pilihan strategi pengendalian, pengendalian yang digunakan dalam arti mengurangi dampakt hama untuk lagi membenarkan status OPT.

R-hama


Tingkat populasi ini selalu berfluktuasi, untuk itu setiap banding ke stabilitas ekosistem alam yg ditakdirkan untuk gagal. Dengan hama tanaman subur dalam kategori tahunan re-invation adalah jalur populasi kunci dan strategi kontrol yang kuat adalah untuk memaksimalkan dificultis di jalur ini. Manipulasi terengah-engah tanggal untuk meminimalkan sinkronisasi rencana hos dan migrasi hama waktu teknik kontrol budaya lain. Perhatian juga harus diberikan kepada kepadatan ekologi dalam dinamika populasi regional spesies tersebut, ini dapat dimanipulasi membuat mereka. reduksi langsung, penghapusan host alternatif adalah salah satu teknik tertua pengendalian hama dan penyakit. Lebih halus hama bisa terlalu penuh di pengungsian sehingga membawa mekanisme yang spesifik ke dalam areal dan musuh alami mungkin mendorong di situs tersebut.
Inti dari dinamika spesies adalah bahwa di sini adalah jurang musuh alami, yang sedikit pun frekuensi yang hama ini mampu tergantung pada banyak faktor, khususnya lebarnya (yang sampai titik tertentu sebanding dengan stabilitas durasi habitat), tingkat ketidakstabilan iklim. Ketika pes tidak endemik maka pengenalan musuh alami yang tepat akan membentuk jurang. Sebagian contoh sukses dari pengendalian biologis termasuk dalam kategori ini.


SUMBER David D.1991.Insect PestManagemen.School of Pure and Aplied Biology,University Of Wales Collage Of Cardiff.

 





the relevance of population dynamic theory



conway (1976) cites the codling moth (cydia pomonella) as a k-pest : it represent an excellent example of a k-pest's normal harvesting having no real impact on the species being harvested, but the level being intolerable to man (clark et al. 1967). elephants always have more impact on their habitat than the codlin moth does on its habitat, but in forest situations in both africa and indonesia the natural populations do not seem to cause significant degradation. however when man cultivates small areas in the pest caregory. tha skylark (alauda arvensis) is a third example of a relatively k-species becoming a pest because, economically, man cannot tolerate its feeding. in the spring in east anglia skylarks often remove a small number of seedling of sugar beet. formerly there were excees seedlings and the stand with specially bred sugar beet fruit containing a single fertile seed have made this bird, the poet's 'blithe spirit', a pest.

a striking instance of the damage caused by a k-species after man has disturbed its regulation is provided by the african elephan (loxondonta african) when is population is confied to game parks. this compression of the population, together with the shootingof the leader matriarchs of the individuals : these mill around on the peripheryb of the park where their activities are causing srious destruction of the trees and other vegetation (laws et al.1975)


a slingtly diffrentn scenario is provided by the bullfinch (pyrrhula pyrrhula) which is now regarded as one of the major pests of fruit growing in souther britain. its large size for a finch and territorial, non-migratory behaviour are k-characteristics. for much of the year the adults are seed feeders, but in the spring the flowering buds of trees form a major part of their diet ; where they are availabel the buds of certain fruit trees are favoured. an individual will take between 15 and 45 buds/minute and will feed for about five hours/day (newton 1964) . thus a singel bullfinch may take some thoussnds of buds per day and a relatively low population may cause a market reduction in the subsequent yield of fruit, a characteristic of a k-pest. it seems that shorteage of food resources in the spring often limits the size of the bullfinch populationb (newton 1964, lack 1966) and thus we may suppose that the development and planting by man of fruit trees with large buds has increased the survival and hence population level of the bullfinch in fruit growing and garden areas. it has been recognized as a pest for over 300 years, but the upsurge in its importance in the last two decades may reflect a further increase in population size due to reduced predation, especially by man (shooting and egg-collecting) but also by raptores another reason for its increased importance in modern crops may be relative because the amount of damage sustained from other causes has been greatly breduce in the last thirty years.

in tropical forests ants frequently play a dominant role in the invertebrate ecosystem: modification of their distribution may allow the increase of other insecta, such as the coreids amblypelta and pseudotheraplus on coconuts, which then cause extensive damage to their hosts (o'connor 1950 way 1953 a and b)

undoubtedly the introduction of plants and animal to new areas is the commonest cause of k-pests. the cocoa tree has been introduced into west africa and the fas east and in both areas among the indigenous insects that have become pest area centain large-sized mirids: sahlbergella singularis , distantiella theobroma, pseudodoniella spp. and platyngomiroides apiformis (leston 1970, conway 1971). in west africa the two former cause considerable damage at relatively low densities (2-4 per tree) to the young shoots of cocoa; their native hosts are various trees, cola spp. adansonia and other malvales, and these suffer less than cocoa (entwistle 1972). the transfer to cocoa in west africa seems to have occurred around 1900 and is undoubtedly a reflection of the general relationship between the number of insect species attached to a tree and its abundace ( southwood 1961, strong 1974): it is noteworthy that there is now some evidence that there may be separate races (entwistle1972). platyngomiroide apiformis was first found on cocoa in sabah in 1962 feeding on pods, later young shoots (chupons) were attacked (lesions axtending up to a foot from the feeding site ) and in 1964 servere and extensive damage to the trunk and branches was seen ( conway 1971). the sensitivity of the new host, to the extent that trees may be killed by relatively small numbers, is a feature of k-pests arising by this mechanism and it is noteworthyvthayvin brazil, where the relationship with the mirid monalonion presumably has a long evolutionary history, the major damage is the pods: unless this is at a very high level it is unlikely to influence the food supply of subsequent generations a feature of k-strategisst.

turning to a completely different part of the trophic web many zoonoses may be regarded as examples of k-pets. these are discussed by garnham (1971, 1977) : for the purpose of this argument it is necessary only to point out the good adaptation of the parasite tp its natural host whose numbers it seldom depletes (the k-strategy); and the extreme sensitivity of the new (unnatural or adventitious) host, in which the parasite may develop new races (c.f.cocoa mirids) and where it behaves essentially as an r-strategist

extremly intersting examples of two k-pests are provided by the african trypanosomes and their vectors, tsetse flies (glossina spp.) conway (1976) has already pointed out the k-strategy characters of tsetse flies and
 it is noteworthy that they are considered to have evolved in association with that K- group par excellence, the large reptiles: on the latter's extinction (apart from crocodiles) tsetse transferred to suidae, which occupied similar habitats and were abundant in the eocene and oligocene, or to other k-strategists-elephants and rhinoceros (ford 1971). The association with antelopes and other mammals is believed to have come later buffalo may have been the first, again because of habitat similarities. The salivaria group of trypanosomes probably arose in leeches, were passed to the suidae and from them infected glossima. The high degree of adjustment to infection of pigs and buffaloes (parasitaemia is infrequent), supports this view (ford 1971). Although some other game animals are more sensitive, especially when young, for most of those regularly bitten by tsetse trypanosomiasis is not lethal. Into this situation man and domestic animals intruded, firstly the negroid races, subsequently the arabs and europeans. In a fascinating account ford (1971) shows how the present status of trypanosomiasis in africa may be related to the distrubances occasioned by the arrival of europeans, their associated diseases (rinderpest, smallpox) and politicial actions.Man and his domestic animals, being the most recently acquired hosts, are the most sensitve to infection by the trypanosomes and in these hosts New races have developed (garnham 1971).
Elm disease (ceratocystis ulmi) has generally behaved like an r-strategist killing most of the trees it attacks its origin is uncertain but we do know that as it is carried around by man more virulent strains develop. Both the fungus and its beetle vector have been carried to the north american continent, exposed to different species of elm and now a new aggressive strain introduced to europe (brasier & gibbs 1973). Perhaps the suckering habit of elm allowed such a lethal parasite to survive or perhaps it was originally more of a k-startegist, killing limbs on old trees over a long period of time. Whichever the case, the present pandemic may enable us to witness an illadapted over virulent race of a parasite exterminating its host and itself, the race resulting from the disturbances to evolved relationships caused by man's movement of flora and fauna around the world.
When consideration has been made for the different biological circumstances of the cocoa mirids, the trypanosomes and elm disease fungus the paralles in the icreased sensitivity the new races and the exploitation (r-strategy) after disturbance are striking.
Pest control strategy and r-k continuum
 Applied bilogists have recognized that habitat charcters are important indicators for pest management strategies ( southwood & way 1970, fig.4) and conway (1976) has shown that as the r-k continnum is related to habitat characteristics it is relevant to decisions on the choice of control strategy, control being used in the sense of reducing the impact of the pest to a level when it no longer justifes pest status. Normally this is done by reducing the population but it may be achieved by breeding for more tolerance (less sensivity) in the victin.
 R-PESTS
 the levels of these populations are always fluctuating therefore any appeal to the stability of natural ecosystem is foredoomed to failure. With arable crop pests in the annual re-invasion is the key population pathway (southwood 1975) and a powerful control strategy is to maximize the difficulties in this pathway. This is analysed by way (1977) the degree of isolation may be increased by greatly enlarging the scale of the crop monoculture and so minimizing the edge effect in the crop and changes can be made in the overwintering, aestivating or alternate hosts sites. The manipulation of planting dates to minimize the synchronization of host plant and pest migration time is another cultural control technique. Attention should also be given to the ecological bottlenecks in the regional population dynamics of such species, these may be manipulated to make them narrower direct reduction the removal of alternate hosts is one of the oldest techniques of pest and disease control. More subtly the pest could be overcrowded in its refuge so bringing intranspecifc mecmanisms into play and natural enemies might be encouraged in these sites as way (1976) suggests for thr aphid myzus persicae. If pest numbers cross the economic injury threshold (norton&conway 1977) pesticides will have to be used to protect the crop the pest population will of course bounce back this is the nature of r-startegists. The crop may be harvested before this happens. A more serious long-tern problem is the potential development of resistance to the pesticide. The high reproductive rates of r-species will favour this but, as comins (1976) shows, provided much of the development of resistance. From economic and biological viewpoints pesticide application must be related to need, this highlights the importance of methods of forecasting and monitoring the pest population (smith 1970). Sometimes forecasts can be based on information about the pest in its overwintering site (refuge or foci of infectio) as with the russia work on the functional morphological condition of the bug eurygaster integriceps (fedotov&bocharova 1955) or the studies on aphis fabae in southern britain (way&cammell 1973). More frequently variations in the success of hibernation, migration and colonization require.monitoring the invading population (taylor 1974) or that in the field (matthews & tunstall 1968)
intermedieate pests
the essence of the dyanamics of these special is that there is a natural enemy ravine : the frequency with which the pest is able to cross this will depend on many factors, particularly its width (which up to a certain point is proportional to the duration stability of the habitat). the degree of climatic instability (i.e. the envronmental noise) and the organisn's own instrinsic rate of increase. it is assumed that the lower equilibrium point (see fig. 2b) is suffciently low that the organism is no longer a pest. this could be invalidated by the increasing emphasis on cosmetic control ( norton & conway 1977). and when thus happens the application of integrated pest control will be difficult. host resistance to attack inevitably lowers the instrinsic rate of increase and so strengthens the ravine.

when the pest is not endemic then the introduction of appropriate natural enemies will establish the ravine. most successful examples of biological control fall into this category and accur in habitats characteristic of intermediete to k-species, rather that r-pests. this is show in table 1.

when intermediate pests are native species it is important that management strategies keep the natural enemy revine intact and widen it if possible : this is the essence of integreted control.

k-pests
the extreme k-strategist is a specialist and will be sensitive to the disturbance of its habitat. therefore k-pests may be reduced by cultural procedures that change thenform of the habitat, for example altering the amount of shade or, for many parasites, reducing the numbers or longevity of another organism (the vector). the majority of k-strategists fail to make the transition fron natural to agroecosystems. the low recruitment rate of these organisms to methods of reproductive control, e.g. sterile male techniques.

canclusion
population dynamics theory has now reached the stage where centain general izations are beginning to appear. the synoptic model is one way of expressing these. it is based on equations for natality, intraspecific competition and natural enemy action which are varied along an axis related to the duration of the habitat and to various bionomic charactera of the organism (size, atc). conveniently described as the r-k continuum. it allows the diversity of nature to be expressed whilst maintaining the uniformity of the underlying equations. pest organisms from anthrax to elephants can be viewed against this framework. it gives useful insights into their origins and the probable success of potential control strategies.