They examined differences between red squirrels and gray squirrels in the American state of Indiana.The scientists wanted to know how these differences could affect the growth of black walnut trees.The black walnut is the nut of choice for both kinds of squirrels.The black walnut tree is also a central part of some hardwood forests.
Rob Swihart of Purdue University did the study with Jake Goheen, a former Purdue student now at the University of New Mexico.The two researchers estimate that several times as many walnuts grow when gathered by gray squirrels as compared to red squirrels.Gray squirrels and red squirrels do not store nuts and seeds in the same way.Gray squirrels bury nuts one at a time in a number of places.But they seldom remember where they buried every nut.So some nuts remain in the ground.Conditions are right for them to develop and grow in the following spring.Red squirrels, however, store large groups of nuts above ground.Professor Swihart calls “death_traps_for_seeds”.
Gray squirrels are native to Indiana.But Professor Swihart says their numbers began to decrease as more forests were cut for agriculture.Red squirrels began to spread through the state during the past century.
The researchers say red squirrels are native to forests that stay green all year, unlike walnut trees.They say the cleaning of forest land for agriculture has helped red squirrels invade Indiana.Jake Goheen calls them a sign of an environmental problem more than a cause.
【全优课堂2017届高考总复习限时规范训练:选修6 unit 5《The power of nature》(新人教版含解析)】相关文章:
★ 2014年牛津译林版高中英语总复习(第1轮)同步练习 M10《Unit 3 Protecting ourselves》Word版含解析
★ 2014届高考英语一轮复习课时作业(四十四)选修8Module 2《The Renaissance》(外研版)
★ 2017届高考英语二轮复习大题冲关秘籍阅读理解七选五:名校模拟(含解析)
★ 2017届高考英语二轮复习书面表达限时测验:5(含解析)
★ 【课堂新坐标】2017届高考英语(通用版)二轮复习书面表达专题训练:Ⅱ卷强化增分练 训练3(含解析)
★ 【优化方案】2017届高考英语二轮复习全国卷Ⅱ规范练:4(含解析)
★ 2014届高考英语一轮复习课时作业(二十五)必修5Module 1《British and American English》(外研版)
★ 【课堂新坐标】2017届高考英语(通用版)二轮复习书面表达专题训练:Ⅱ卷强化增分练 训练1(含解析)
★ 【课堂新坐标】2017届高考英语(通用版)二轮复习书面表达专题训练:训练5 书信、邮件+说明文(含解析)
★ 【北师大版】2014届高考英语一轮复习指导课时作业:Unit 9 B卷 Word版含解析
最新
2017-04-24
2017-04-24
2017-04-24
2017-04-24
2017-04-21
2017-04-21