47.3: Vitisho kwa Biodiversity
- Page ID
- 176264
Ujuzi wa Kuendeleza
- Kutambua vitisho muhimu kwa viumbe hai
- Eleza madhara ya hasara ya makazi, aina ya kigeni, na uwindaji juu ya viumbe hai
- Kutambua madhara mapema na alitabiri ya mabadiliko ya hali ya hewa juu ya viumbe hai
Tishio la msingi kwa viumbe hai duniani, na hivyo tishio kwa ustawi wa binadamu, ni mchanganyiko wa ukuaji wa idadi ya watu na unyonyaji wa rasilimali. Idadi ya watu inahitaji rasilimali kuishi na kukua, na rasilimali hizo zinaondolewa bila kudumu kutoka kwenye mazingira. Vitisho vitatu vikubwa zaidi vya viumbe hai ni kupoteza makazi, overbrevening, na kuanzishwa kwa aina za kigeni. Hizi mbili za kwanza ni matokeo ya moja kwa moja ya ukuaji wa idadi ya watu na matumizi ya rasilimali. Matokeo ya tatu kutokana na kuongezeka kwa uhamaji na biashara. Sababu kuu ya nne ya kutoweka, mabadiliko ya hali ya hewa ya anthropogenic, bado haijawahi kuwa na athari kubwa, lakini inatabiriwa kuwa muhimu wakati wa karne hii. Mabadiliko ya hali ya hewa duniani pia ni matokeo ya mahitaji ya idadi ya watu kwa ajili ya nishati na matumizi ya mafuta ya mafuta ili kukidhi mahitaji hayo (Kielelezo\(\PageIndex{1}\)). Masuala ya mazingira, kama vile uchafuzi wa sumu, yana athari maalum kwa spishi, lakini hazionekani kwa ujumla kama vitisho kwa ukubwa wa wengine.
Habitat hasara
Binadamu wanategemea teknolojia ili kurekebisha mazingira yao na kuchukua nafasi ya kazi fulani zilizowahi kufanywa na mazingira ya asili. Spishi nyingine haziwezi kufanya hivyo. Kuondokana na mfumo wa mazingira yao-iwe ni msitu, jangwa, mbuga, maji safi ya maji safi, au mazingira ya baharini-itawaua watu binafsi katika aina. Ondoa makazi yote ndani ya aina mbalimbali za aina na, isipokuwa ni moja ya spishi chache zinazofanya vizuri katika mazingira yaliyojengwa na binadamu, aina hiyo itakuwa haiko. Uharibifu wa binadamu wa makazi uliharakisha katika nusu ya mwisho ya karne ya ishirini. Fikiria viumbe hai wa kipekee wa Sumatra: ni nyumbani kwa aina moja ya orangutan, aina ya tembo hatari sana, na tiger ya Sumatran, lakini nusu ya misitu ya Sumatra sasa imekwenda. Kisiwa jirani cha Borneo, nyumbani kwa aina nyingine za orangutan, kimepoteza eneo sawa la misitu. Hasara ya misitu inaendelea katika maeneo ya ulinzi wa Borneo. Orangutan katika Borneo imeorodheshwa kama hatarini na Umoja wa Kimataifa wa Uhifadhi wa Nature (IUCN), lakini ni tu inayoonekana zaidi ya maelfu ya spishi ambazo hazitaishi kutoweka kwa misitu ya Borneo. Misitu huondolewa kwa miti na kupanda mimea ya mafuta ya mitende (Kielelezo\(\PageIndex{2}\)). Mafuta ya mitende hutumiwa katika bidhaa nyingi ikiwa ni pamoja na bidhaa za chakula, vipodozi, na biodiesel barani Ulaya. Makadirio ya miaka mitano ya kupoteza bima ya misitu duniani kwa miaka 2000—2005 ilikuwa asilimia 3.1. Katika nchi za hari za mvua ambako hasara ya misitu ni hasa kutokana na uchimbaji wa mbao, kilomita 272,000 2 ilipotea kati ya jumla ya kimataifa ya km 11,564,000 2 (au asilimia 2.4). Katika kitropiki, hasara hizi hakika pia zinawakilisha kutoweka kwa spishi kwa sababu ya viwango vya juu vya endemism.
Uunganisho wa Kila siku: Kuzuia Uharibifu wa Habitat na Uchaguzi
Wateja wengi hawafikiri kwamba bidhaa za kuboresha nyumbani wanazonunua zinaweza kuchangia kupoteza makazi na kutengwa kwa aina. Hata hivyo soko la miti ya kitropiki iliyovunwa kinyume cha sheria ni kubwa, na bidhaa za mbao mara nyingi hujikuta katika kujenga maduka ya usambazaji nchini Marekani. Makadirio moja ni kwamba asilimia 10 ya mkondo wa mbao ulioagizwa nchini Marekani, ambao ndio mtumiaji mkubwa zaidi duniani wa bidhaa za mbao, huenda huenda ukiingia kinyume cha sheria. Mwaka 2006, hii ilifikia dola bilioni 3.6 katika bidhaa za kuni. Wengi wa bidhaa haramu ni nje kutoka nchi ambazo hufanya kazi kama waamuzi na si waanzilishi wa kuni.
Inawezekanaje kuamua kama bidhaa za kuni, kama sakafu, zilivunwa kwa kudumu au hata kisheria? Baraza la Usimamizi wa Misitu (FSC) linathibitisha bidhaa za msitu zinazoendelea kuvuna, kwa hiyo, kutafuta vyeti vyao juu ya sakafu na bidhaa nyingine za ngumu ni njia moja ya kuhakikisha kuwa kuni haijachukuliwa kinyume cha sheria kutoka msitu wa kitropiki. Vyeti inatumika kwa bidhaa maalum, si kwa mtayarishaji; baadhi ya bidhaa wazalishaji 'inaweza kuwa na vyeti wakati bidhaa nyingine ni kuthibitishwa. Ingawa kuna vyeti vingine vinavyoungwa mkono sekta isipokuwa FSC, hizi haziaminiki kutokana na ukosefu wa uhuru kutoka sekta hiyo. Njia nyingine ni kununua aina za miti za ndani. Wakati itakuwa kubwa kama kulikuwa na orodha ya kisheria dhidi ya bidhaa haramu mbao, si rahisi. Sheria za uandikishaji na usimamizi wa misitu hutofautiana kutoka nchi hadi nchi; kile ambacho ni kinyume cha sheria katika nchi moja kinaweza kuwa halali katika nchi nyingine. Wapi na jinsi bidhaa inavyovunwa na kama msitu ambao huja unasimamiwa endelevu kila kitu katika kama bidhaa za kuni zitathibitishwa na FSC. Daima ni wazo nzuri kuuliza maswali kuhusu wapi bidhaa za kuni zilikuja na jinsi muuzaji anajua kwamba ilivunwa kisheria.
Uharibifu wa mazingira unaweza kuathiri mazingira mengine ya misitu. Mito na mito ni mazingira muhimu na mara nyingi hubadilishwa kupitia maendeleo ya ardhi na kutoka kwa damming au kuondolewa kwa maji. Damming ya mito huathiri mtiririko wa maji na upatikanaji wa sehemu zote za mto. Utawala tofauti wa mtiririko unaweza kupunguza au kuondokana na idadi ya watu ambao hubadilishwa na mabadiliko haya katika mifumo ya mtiririko. Kwa mfano, wastani wa asilimia 91 ya urefu wa mto nchini Marekani umeendelezwa: wana marekebisho kama mabwawa, kuunda nishati au kuhifadhi maji; levees, kuzuia mafuriko; au dredging au relouting, kujenga ardhi inayofaa zaidi kwa maendeleo ya binadamu. Spishi nyingi za samaki nchini Marekani, hasa spishi za nadra au spishi zenye mgawanyo vikwazo, zimeona kupungua kwa sababu ya damming ya mto na kupoteza makazi. Utafiti umethibitisha kwamba spishi za amfibia zinazopaswa kutekeleza sehemu za mizunguko yao ya maisha katika makazi yote ya majini na ya duniani huwa na nafasi kubwa ya kuteseka idadi ya watu kupungua na kutoweka kwa sababu ya uwezekano ulioongezeka kuwa mojawapo ya makazi yao au upatikanaji kati yao yatapotea.
Kuvunja kupita kiasi
Kuvunja zaidi ni tishio kubwa kwa aina nyingi, lakini hasa kwa aina za majini. Kuna mifano mingi ya uvuvi wa kibiashara unaodhibitiwa kufuatiliwa na wanasayansi wa uvuvi ambao hata hivyo wameanguka. Uvuvi wa magharibi wa Atlantic cod ni kuanguka kwa hivi karibuni zaidi. Wakati ilikuwa uvuvi mkubwa wa uzalishaji kwa miaka 400, kuanzishwa kwa mitambo ya kisasa ya kiwanda katika miaka ya 1980 na shinikizo kwa uvuvi kulisababisha kuwa haiwezi kudumu. Sababu za kuanguka kwa uvuvi ni za kiuchumi na kisiasa katika asili. Uvuvi wengi husimamiwa kama rasilimali ya kawaida (pamoja) hata wakati eneo la uvuvi liko ndani ya maji ya eneo la nchi. Rasilimali za kawaida zinakabiliwa na shinikizo la kiuchumi linalojulikana kama janga la kawaida ambalo kimsingi hakuna wavuvi ana motisha ya kuzuia kuvuna uvuvi wakati haimiliki na wavuvi huyo. Matokeo ya asili ya mavuno ya rasilimali yaliyofanyika kwa pamoja ni unyanyasaji wao mkubwa. Wakati uvuvi mkubwa umewekwa ili kujaribu kuepuka shinikizo hili, bado lipo nyuma. Unyanyasaji huu unazidishwa wakati upatikanaji wa uvuvi ni wazi na usio na udhibiti na wakati teknolojia inapowapa wavuvi uwezo wa overfish. Katika uvuvi wachache, ukuaji wa kibiolojia wa rasilimali ni chini ya ukuaji wa uwezo wa faida inayotokana na uvuvi ikiwa wakati huo na pesa ziliwekeza mahali pengine. Katika kesi hizi-nyangumi ni mfano—vikosi vya kiuchumi vitaendesha gari kuelekea uvuvi idadi ya watu ili kutoweka.
Unganisha na Kujifunza
Kuchunguza Marekani Samaki & Wanyamapori Service ramani shirikishi ya mazingira muhimu kwa ajili ya aina hatarini na kutishiwa nchini Marekani. Kuanza, chagua “Tembelea ramani ya mtandaoni.”
Kwa sehemu kubwa, kutoweka kwa uvuvi si sawa na kutengwa kwa kibiolojia-samaki wa mwisho wa spishi ni mara chache huvuja nje ya bahari. Wakati huo huo, kutoweka kwa uvuvi bado kuna hatari kwa aina za samaki na mazingira yao. Kuna baadhi ya matukio ambayo kutoweka kweli ni uwezekano. Nyangumi wana idadi ya watu wanaokua polepole na wako katika hatari ya kutoweka kabisa kwa njia ya uwindaji. Kuna baadhi ya spishi za papa wenye mgawanyo uliozuiliwa ambao wako hatarini mwa kutoweka. Vikundi ni idadi nyingine ya samaki wanaokua polepole ambao, katika Karibi, hujumuisha aina kadhaa ambazo ziko hatarini mwa kutoweka kutokana na uvuvi mkubwa.
Miamba ya matumbawe ni mazingira tofauti ya baharini ambayo yanakabiliwa na hatari kutoka kwa michakato kadhaa. Miamba ni nyumbani kwa 1/3 ya aina ya samaki baharini duniani—kuhusu aina 4,000- licha ya kutengeneza asilimia 1 tu ya makazi ya baharini. Wengi nyumbani aquaria baharini ni kujaa na viumbe pori-hawakupata, si viumbe cultured. Ingawa hakuna spishi inayojulikana kuwa imefukuzwa kutoweka na biashara ya wanyama katika spishi za baharini, kuna tafiti zinazoonyesha kuwa idadi ya spishi fulani yamepungua kwa kukabiliana na kuvuna, ikionyesha kuwa mavuno hayawezi endelevu katika ngazi hizo. Kuna wasiwasi kuhusu athari za biashara ya wanyama kwenye aina fulani za nchi kama vile turtles, amfibia, ndege, mimea, na hata orangutan.
Nyama ya Bush ni neno la kawaida linalotumika kwa wanyama pori waliouawa kwa ajili ya chakula. Uwindaji unafanywa duniani kote, lakini mazoea ya uwindaji, hasa katika Afrika ya ikweta na sehemu za Asia, huaminiwa kutishia spishi kadhaa kwa kutoweka. Kijadi, kichaka nyama katika Afrika ilikuwa kuwindwa kulisha familia moja kwa moja; hata hivyo, hivi karibuni kibiashara ya mazoezi sasa ina kichaka nyama inapatikana katika maduka ya vyakula, ambayo imeongeza viwango vya mavuno kwa kiwango cha kutokuwa endelevu. Zaidi ya hayo, ukuaji wa idadi ya watu umeongeza haja ya vyakula vya protini ambavyo havipatikani kutokana na kilimo. Spishi zinazotishiwa na biashara ya nyama ya kichaka ni zaidi mamalia wakiwemo primates wengi wanaoishi katika beseni la Kongo.
Aina ya kigeni
Spishi za kigeni ni spishi ambazo zimeletwa kwa makusudi au bila kukusudia na wanadamu kuwa mazingira ambayo hayakufuka. Utangulizi huo uwezekano kutokea mara kwa mara kama matukio ya asili. Kwa mfano, Kudzu (Pueraria lobata), ambayo ni asili ya Japan, ilianzishwa nchini Marekani mwaka 1876. Baadaye ilipandwa kwa ajili ya uhifadhi wa udongo. Kwa shida, inakua vizuri sana katika kusini mashariki mwa Marekani-hadi mguu kwa siku. Kwa sasa ni aina ya wadudu na inashughulikia zaidi ya ekari milioni 7 katika kusini mashariki mwa Marekani. Ikiwa aina iliyoanzishwa ina uwezo wa kuishi katika makazi yake mapya, utangulizi huo sasa unaonekana katika aina mbalimbali za aina. Usafiri wa binadamu wa watu na bidhaa, ikiwa ni pamoja na usafiri wa makusudi wa viumbe kwa ajili ya biashara, umeongeza sana kuanzishwa kwa spishi katika mazingira mapya, wakati mwingine katika umbali ambao ni vizuri zaidi ya uwezo wa spishi ya milele kusafiri yenyewe na nje ya aina mbalimbali za spishi ' predators asili.
Wengi kigeni aina utangulizi pengine kushindwa kwa sababu ya idadi ndogo ya watu kuletwa au kukabiliana na hali mbaya kwa mazingira wao kuingia. Baadhi ya aina, hata hivyo, wamiliki preadaptations ambayo inaweza kuwafanya hasa mafanikio katika mazingira mapya. Spishi hizi za kigeni mara nyingi hupata ongezeko kubwa la idadi ya watu katika makazi yao mapya na kuweka upya hali ya kiikolojia katika mazingira mapya, na kutishia spishi zilizopo huko. Kwa sababu hii, aina za kigeni pia huitwa aina za uvamizi. Spishi za kigeni zinaweza kutishia spishi nyingine kwa njia ya ushindani wa rasilimali, predation, au ugonjwa.
Maziwa na visiwa ni hatari zaidi ya vitisho vya kutoweka kutoka kwa aina zilizoanzishwa. Katika Ziwa Victoria, kama ilivyoelezwa hapo awali, kuanzishwa kwa makusudi ya sangara ya Nile ilikuwa kwa kiasi kikubwa kuwajibika kwa kutoweka kwa aina 200 za cichlids. Kuanzishwa kwa ajali ya nyoka kahawia mti kupitia ndege (Kielelezo\(\PageIndex{3}\)) from the Solomon Islands to Guam in 1950 has led to the extinction of three species of birds and three to five species of reptiles endemic to the island. Several other species are still threatened. The brown tree snake is adept at exploiting human transportation as a means to migrate; one was even found on an aircraft arriving in Corpus Christi, Texas. Constant vigilance on the part of airport, military, and commercial aircraft personnel is required to prevent the snake from moving from Guam to other islands in the Pacific, especially Hawaii. Islands do not make up a large area of land on the globe, but they do contain a disproportionate number of endemic species because of their isolation from mainland ancestors.
It now appears that the global decline in amphibian species recognized in the 1990s is, in some part, caused by the fungus Batrachochytrium dendrobatidis, which causes the disease chytridiomycosis (Figure \(\PageIndex{4}\)). There is evidence that the fungus is native to Africa and may have been spread throughout the world by transport of a commonly used laboratory and pet species: the African clawed toad (Xenopus laevis). It may well be that biologists themselves are responsible for spreading this disease worldwide. The North American bullfrog, Rana catesbeiana, which has also been widely introduced as a food animal but which easily escapes captivity, survives most infections of Batrachochytrium dendrobatidis and can act as a reservoir for the disease.
Early evidence suggests that another fungal pathogen, Geomyces destructans, introduced from Europe is responsible for white-nose syndrome, which infects cave-hibernating bats in eastern North America and has spread from a point of origin in western New York State (Figure \(\PageIndex{5}\)). The disease has decimated bat populations and threatens extinction of species already listed as endangered: the Indiana bat, Myotis sodalis, and potentially the Virginia big-eared bat, Corynorhinus townsendii virginianus. How the fungus was introduced is unclear, but one logical presumption would be that recreational cavers unintentionally brought the fungus on clothes or equipment from Europe.
Climate Change
Climate change, and specifically the anthropogenic (meaning, caused by humans) warming trend presently underway, is recognized as a major extinction threat, particularly when combined with other threats such as habitat loss. Scientists disagree about the likely magnitude of the effects, with extinction rate estimates ranging from 15 percent to 40 percent of species committed to extinction by 2050. Scientists do agree, however, that climate change will alter regional climates, including rainfall and snowfall patterns, making habitats less hospitable to the species living in them. The warming trend will shift colder climates toward the north and south poles, forcing species to move with their adapted climate norms while facing habitat gaps along the way. The shifting ranges will impose new competitive regimes on species as they find themselves in contact with other species not present in their historic range. One such unexpected species contact is between polar bears and grizzly bears. Previously, these two species had separate ranges. Now, their ranges are overlapping and there are documented cases of these two species mating and producing viable offspring. Changing climates also throw off species’ delicate timing adaptations to seasonal food resources and breeding times. Many contemporary mismatches to shifts in resource availability and timing have already been documented.
Range shifts are already being observed: for example, some European bird species ranges have moved 91 km northward. The same study suggested that the optimal shift based on warming trends was double that distance, suggesting that the populations are not moving quickly enough. Range shifts have also been observed in plants, butterflies, other insects, freshwater fishes, reptiles, and mammals.
Climate gradients will also move up mountains, eventually crowding species higher in altitude and eliminating the habitat for those species adapted to the highest elevations. Some climates will completely disappear. The rate of warming appears to be accelerated in the arctic, which is recognized as a serious threat to polar bear populations that require sea ice to hunt seals during the winter months: seals are the only source of protein available to polar bears. A trend to decreasing sea ice coverage has occurred since observations began in the mid-twentieth century. The rate of decline observed in recent years is far greater than previously predicted by climate models.
Finally, global warming will raise ocean levels due to melt water from glaciers and the greater volume of warmer water. Shorelines will be inundated, reducing island size, which will have an effect on some species, and a number of islands will disappear entirely. Additionally, the gradual melting and subsequent refreezing of the poles, glaciers, and higher elevation mountains—a cycle that has provided freshwater to environments for centuries—will also be jeopardized. This could result in an overabundance of salt water and a shortage of fresh water.
Summary
The core threats to biodiversity are human population growth and unsustainable resource use. To date, the most significant causes of extinctions are habitat loss, introduction of exotic species, and overharvesting. Climate change is predicted to be a significant cause of extinctions in the coming century. Habitat loss occurs through deforestation, damming of rivers, and other activities. Overharvesting is a threat particularly to aquatic species, while the taking of bush meat in the humid tropics threatens many species in Asia, Africa, and the Americas. Exotic species have been the cause of a number of extinctions and are especially damaging to islands and lakes. Exotic species’ introductions are increasing because of the increased mobility of human populations and growing global trade and transportation. Climate change is forcing range changes that may lead to extinction. It is also affecting adaptations to the timing of resource availability that negatively affects species in seasonal environments. The impacts of climate change are greatest in the arctic. Global warming will also raise sea levels, eliminating some islands and reducing the area of all others.
Art Connections
Converting a prairie to a farm field is an example of ________.
- overharvesting
- habitat loss
- exotic species
- climate change
- Answer
-
B
Glossary
- bush meat
- wild-caught animal used as food (typically mammals, birds, and reptiles); usually referring to hunting in the tropics of sub-Saharan Africa, Asia, and the Americas
- chytridiomycosis
- disease of amphibians caused by the fungus Batrachochytrium dendrobatidis; thought to be a major cause of the global amphibian decline
- exotic species
- (also, invasive species) species that has been introduced to an ecosystem in which it did not evolve
- tragedy of the commons
- economic principle that resources held in common will inevitably be overexploited
- white-nose syndrome
- disease of cave-hibernating bats in the eastern United States and Canada associated with the fungus Geomyces destructans