most exotic species are introduced into a new environment accidentally as a result of human travel.
most exotic species are introduced into a new environment accidentally as a result of human travel.
most exotic species are introduced into a new environment accidentally as a result of?
human travel
unintentional introductions occur when species are transported by human vectors. increasing rates of human travel are providing accelerating opportunities for species to be accidentally transported into areas in which they are not considered native. for example, three species of rat (the black, norway and polynesian) have spread to most of the world as hitchhikers on ships, and arachnids such as scorpions and exotic spiders are sometimes transported to areas far beyond their native range by riding in shipments of tropical fruit. there are also numerous examples of marine organisms being transported in ballast water, one being the zebra mussel. over 200 species have been introduced to the san francisco bay in this manner making it the most heavily invaded estuary in the world. there is also the accidental release of the africanized honey bees (ahb), known colloquially as "killer bees" or africanized bee to brazil in 1957 and the asian carps to the united states. the insect commonly known as the brown marmorated stink bug ("halyomorpha halys") was introduced accidentally in pennsylvania. another form of unintentional introductions is when an intentionally introduced plant carries a parasite or herbivore with it. some become invasive, for example the oleander aphid, accidentally introduced with the ornamental plant, oleander.
introduced species
fish species and the development of fisheries in lugu lake have been researched during 2001, 2002 and 2004. the studies reported that there are now 12 fish species in lugu lake, which belong to 10 genera, four families and three orders. changes to the proliferation of fish in the lake has been due to the deposition of silt in the lake following heavy deforestation of lake's catchment. in addition to the four endemic species, eight exotic species were identified and these dominate the fish population in the lake to the detriment of the endemic species. fishing is normally carried out using gillnets. the nets are spread over the lake’s entire length and width at different depths with mesh size varying to suit needs; they are usually spread from late afternoon to the morning hours of the following day. the eight exotic species, introduced to the lake in 1958 as part of commercial fishing activity, dominate the fishing resources of the lake, and three of the native species have been declared endangered. as a result of commercial fishing activity, the fish resources initially netted amounted to 500 tonnes. however, overfishing in the last few decades by trawlers has resulted in a drastic decline of the yield and in 1980 it was reported to be only 30 tonnes. the main reasons attributed for this decline are the heavy deforestation that occurred once in 1970 and then again between 1980 and 1990, which caused heavy siltation of the lake; the siltation advanced into the lake causing destruction of many spawning grounds of the three "schizothorax" fishes, followed by the decrease of their stocks. another reason given for the decrease in endemic fish stocks is the introduction of the exotic species, which has led to a decline in the indigenous "schizothoracid" species.
lugu lake