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‫‪‬‬

‫‪‬‬
‫‪‬‬

‫‪ ‬‬ ‫‪‬‬ ‫‪‬‬
‫‪‬‬

‫‪ í‬ﺍﻟﺸـﻜﻞ ‪ 4-10‬ﻳﺆﺛﺮ ﻧﻘﺺ ﺃﺣﺪ ﺍﻷﻧﻮﺍﻉ‬ ‫ا‪‬س‪‬را‪ ‬المو‪ ‬البيئ‪ Disruption of habitat ‬ﻗـﺪ ﻻ ﹸﺗﺪﻣـﺮ ﺍﻟﻤﻮﺍﻃـﻦ ﺍﻟﺒﻴﺌﻴﺔ ﺑﻞ‬
‫ﰲ ﺍﻟﻨﻈـﺎﻡ ﺍﻟﺒﻴﺌﻲ ﻛﺎﻣ ﹰﻼ‪ .‬ﻓﻌﻨﺪﻣـﺎ ﺗﻨﻘﺺ ﺃﻋﺪﺍﺩ‬ ‫ﻳﺤﺪﺙ ﻓﻴﻬﺎ ﺍﺧﺘﺰﺍﻝ‪ .‬ﻓﻤﺜ ﹰﻼ ﻇﻬﺮﺕ ﺳﻠﺴﻠﺔ ﺃﺣﺪﺍﺙ ﻓﻲ ﺍﻟﺴﺒﻌﻴﻨﻴﺎﺕ ﻣﻦ ﻫﺬﺍ ﺍﻟﻘﺮﻥ ﺗﻮﺿﺢ‬
‫ﻓﻘﻤﺔ ﺍﳌﻮﺍﻧﺊ ﻭﺃﺳﻮﺩ ﺍﻟﺒﺤﺮ‪ ،‬ﻳﺒﺪﺃ ﺍﳊﻮﺕ ﺍﻟﻘﺎﺗﻞ‬ ‫ﺃﻥ ﻧﻘﺺ ﺃﻋﺪﺍﺩ ﺃﺣﺪ ﻋﻨﺎﺻﺮ ﺍﻟﺸﺒﻜﺔ ﺍﻟﻐﺬﺍﺋﻴﺔ ﻳﺆﺛﺮ ﻓﻲ ﺍﻟﻌﻨﺎﺻﺮ ﺍﻷﺧﺮ￯‪ .‬ﻭﻛﻤﺎ ﺗﻼﺣﻆ ﻣﻦ‬
‫ﺑﺎﻟﺘﻐﺬﻱ ﻋﲆ ﺍﻟﻘﻀﺎﻋـﺔ‪ ،‬ﻭﻧﺘﻴﺠﺔ ﻟﻨﻘﺼﺎﻥ ﻋﺪﺩ‬ ‫ﺍﻟﻤﺨﻄﻂ ﺍﻟﻤﺒﻴﻦ ﻓﻲ ﺍﻟﺸﻜﻞ ‪ 4-10‬ﻓﺈﻥ ﻧﻘﺺ ﺃﺣﺪ ﺍﻷﻧﻮﺍﻉ ﻳﺆﺛﺮ ﻓﻲ ﺍﻟﻨﻈﺎﻡ ﺍﻟﺒﻴﺌﻲ ﺑﺄﻛﻤﻠﻪ‪.‬‬
‫ﺍﻟﻘﻀﺎﻋـﺎﺕ ﺗـﺰﺩﺍﺩ ﺃﻋـﺪﺍﺩ ﻗﻨﺎﻓـﺬ ﺍﻟﺒﺤـﺮ ﺍﻟﺘﻲ‬ ‫ﻭﺇﺫﺍ ﻛﺎﻥ ﻷﺣﺪ ﺍﻷﻧﻮﺍﻉ ﺩﻭﺭ ﻛﺒﻴﺮ ﻓﻲ ﺍﻟﻨﻈﺎﻡ ﺍﻟﺒﻴﺌﻲ ﻓﻴﺴﻤﻰ ﻫﺬﺍ ﺍﻟﻨﻮﻉ ﺣﺠﺮ ﺍﻷﺳﺎﺱ‪ .‬ﻓﻤﺜ ﹰﻼ‬
‫ﺗﺘﻐـﺬ￯ ﻋـﲆ ﻋﺸـﺐ ﺍﻟﺒﺤـﺮ‪ ،‬ﻭﻫﺬﺍ ﻳـﺆﺩﻱ ﺇﱃ‬ ‫ﻧﻘﺼﺎﻥ ﻣﺠﻤﻮﻋﺎﺕ ﺍﻟﺴـﻤﻚ ﺍﻟﻤﺨﺘﻠﻔـﺔ ﻧﺘﻴﺠ ﹰﺔ ﻟﻠﺼﻴﺪ ﺍﻟﺠﺎﺋﺮ ﻳـﺆﺩﻱ ﺇﻟﻰ ﻧﻘﺺ ﻓﻲ ﺃﻋﺪﺍﺩ‬
‫ﺃﺳـﺪ ﺍﻟﺒﺤﺮ ﻭﻓﻘﻤﺔ ﺍﻟﻤﻮﺍﻧـﺊ‪ .‬ﻭﻗﺪ ﺍﻓﺘﺮﺽ ﺑﻌﺾ ﺍﻟﻌﻠﻤﺎﺀ ﺃﻥ ﻇﺎﻫـﺮﺓ ﺍﻻﺣﺘﺒﺎﺱ ﺍﻟﺤﺮﺍﺭﻱ‬
‫ﺍﻻﺧﺘﻼﻝ ﰲ ﻏﺎﺑﺎﺕ ﻋﺸﺐ ﺍﻟﺒﺤﺮ‪.‬‬ ‫ﺍﻟﻌﺎﻟﻤـﻲ ﻟﻜﻮﻛﺐ ﺍﻷﺭﺽ ﻗـﺪ ﻟﻌﺒﺖ ﺩﻭ ﹰﺭﺍ ﻓﻲ ﻫﺬﺍ ﺍﻟﻨﻘﺼﺎﻥ‪ ،‬ﻓﻘـﺪ ﺃﺩﺕ ﻫﺬﻩ ﺍﻟﻈﺎﻫﺮﺓ ﺇﻟﻰ‬

‫ﺳﻠﺴﻠﺔ ﺗﻔﺎﻋﻼﺕ ﺩﺍﺧﻞ ﺍﻟﻨﻈﺎﻡ ﺍﻟﺒﻴﺌﻲ ﺍﻟﺒﺤﺮﻱ ﺍﻟﺬﻱ ﺃ ﹼﺛﺮ ﻓﻲ ﺍﻟﻜﺜﻴﺮ ﻣﻦ ﺍﻷﻧﻮﺍﻉ‪.‬‬

‫م‪‬ا ‪‬راأ‪ ‬س‪ ‬م ﺍﻟﺤﻴـﻮﺍﻥ ﺍﻟـﺬﻱ ﻳﻌـ ﹼﺪ ﺣﺠـﺮ ﺍﻷﺳـﺎﺱ ﻓـﻲ ﺍﻟﻨﻈـﺎﻡ ﺍﻟﺒﻴﺌـﻲ ﻓـﻲ‬
‫ﺍﻟﺸﻜﻞ ‪.4-10‬‬

‫‪‬ة المو‪ ‬البيئ‪ Fragmentation of habitat ‬ﻳﺴﻤﻰ ﺍﻧﻔﺼﺎﻝ ﺍﻟﻨﻈﺎﻡ ﺍﻟﺒﻴﺌﻲ‬

‫ﺇﻟﻰ ﺃﺟﺰﺍﺀ ﺻﻐﻴﺮﺓ ﻣﻦ ﺍﻷﺭﺽ ﺗﺠﺰﺋﺔ ﺍﻟﻤﻮﻃﻦ ﺍﻟﺒﻴﺌﻲ ‪ .habitat Fragmentation‬ﺗﺒﻘﻰ‬
‫ﺍﻟﺠﻤﺎﻋـﺎﺕ ﺍﻟﺤﻴﻮﻳـﺔ ﺍﻟﺤﺎﻟﻴﺔ ﻏﺎﻟ ﹰﺒﺎ ﺿﻤـﻦ ﺣﺪﻭﺩ ﻗﻄﻌﺔ ﺍﻷﺭﺽ ﺍﻟﺼﻐﻴـﺮﺓ ﻫﺬﻩ ﻷﻧﻬﺎ ﻏﻴﺮ‬
‫ﻗﺎﺩﺭﺓ ﺃﻭ ﻏﻴﺮ ﺭﺍﻏﺒﺔ ﻓﻲ ﻋﺒﻮﺭ ﺍﻟﺤﻮﺍﺟﺰ ﺍﻟﺘﻲ ﺻﻨﻌﻬﺎ ﺍﻹﻧﺴـﺎﻥ‪ .‬ﻭﻳﺆﺩﻱ ﻫﺬﺍ ﺇﻟﻰ ﺍﻟﻌﺪﻳﺪ ﻣﻦ‬

‫ﺍﻟﻤﺸﻜﻼﺕ ﺍﻟﺘﻲ ﺗﺆﺛﺮ ﻓﻲ ﺑﻘﺎﺀ ﺍﻷﻧﻮﺍﻉ ﺍﻟﺤﻴﺔ ﺍﻟﻤﺘﻨﻮﻋﺔ‪ ،‬ﻭﻣﻨﻬﺎ‪:‬‬

‫ﺃﻭ ﹰﻻ‪ :‬ﻛﻠﻤـﺎ ﻛﺎﻧـﺖ ﻗﻄﻌﺔ ﺍﻷﺭﺽ ﺃﺻﻐـﺮ ﻓﺈﻧﻬﺎ ﺗﺪﻋﻢ ﻋـﺪ ﹰﺩﺍ ﺃﻗﻞ ﻣﻦ ﺍﻷﻧـﻮﺍﻉ‪ .‬ﺛﺎﻧ ﹰﻴﺎ‪ :‬ﺗﻘ ﱢﻠﻞ‬
‫ﺍﻟﺘﺠﺰﺋـﺔ ﻣﻦ ﻓﺮﺹ ﺗﻜﺎﺛﺮ ﺍﻷﻓﺮﺍﺩ ﻓﻲ ﻣﻨﻄﻘﺔ ﻣﺎ ﻣﻊ ﺃﻓـﺮﺍﺩ ﺁﺧﺮﻳﻦ ﻣﻦ ﻣﻨﻄﻘﺔ ﺃﺧﺮ￯‪ .‬ﻭﻟﻬﺬﺍ‬
‫ﺍﻟﺴـﺒﺐ ﻏﺎﻟ ﹰﺒـﺎ ﻣﺎ ﻳﻘﻞ ﺍﻟﺘﻨـﻮﻉ ﺍﻟﻮﺭﺍﺛﻲ ﻣﻊ ﻣـﺮﻭﺭ ﺍﻟﻮﻗﺖ ﻓﻲ ﺣﺎﻟﺔ ﺗﺠﺰﺋـﺔ ﺍﻟﻤﻮﻃﻦ ﺍﻟﺒﻴﺌﻲ‪.‬‬
‫ﻓﺎﻟﺠﻤﺎﻋـﺎﺕ ﺍﻟﺤﻴﻮﻳـﺔ ﺍﻷﺻﻐﺮ ﻭﺍﻟﻤﻨﻔﺼﻠـﺔ ﻭﺫﺍﺕ ﺍﻟﺘﻨﻮﻉ ﺍﻟﻮﺭﺍﺛﻲ ﺍﻟﺒﺴـﻴﻂ ﺃﻗـﻞ ﻣﻘﺎﻭﻣ ﹰﺔ‬

‫ﻟﻸﻣﺮﺍﺽ ﺃﻭ ﺍﺳﺘﺠﺎﺑ ﹰﺔ ﻟﺘﻐﻴﺮﺍﺕ ﺍﻟﻈﺮﻭﻑ ﺍﻟﺒﻴﺌﻴﺔ‪.‬‬

‫ﻣﺩﺭﺳﺔ ﺍﻟﺟﻳﻭﻟﻭﺟﻳﺎ ‪115‬‬
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