1 . Mutualism—win-win ecological partnerships perfected over evolutionary time-lengths—is a less-known ecological relationship that is also weak and easily hurt by the effect of a rapidly changing planet.
Bees and flowers are typical examples of mutualism. Some bee tongues are perfectly evolved to tap into certain flowers. By specializing in those plants, the longer-tongued bees reduce competition with insects that can't access those sweet foods.
That mutualistic relationship, however, has been impacted in at least one population of bees and flowers. As certain flowers in Colorado have become rarer due to warming temperatures, the tongues of the bumblebees（大黄蜂）that historically fed on them have become shorter.
Like many of their relatives, bumblebees are on the decline. To find out what's going on, a team of researchers headed to Colorado. The researchers examined bumblebee samples collected on three mountains from 1966 to 1980 and also gathered a fresh set, which they collected in the same places from 2012 to 2014. They performed the task of measuring all the historic and recently caught bees' tongues.
As the team reports in Science, both of the species tongues have declined in length over time. The team found a nearly 25-percent decrease in tongue length between the bees collected decades ago and those living in the same region today.
Next they turned to the flowers. Looking at contemporary and historic botanical data, the scientists confirmed that the number of flowers with short tubes did not increase in large quantities. They found that in response to warmer temperatures, flowers have been moving up the mountains and becoming rarer at lower altitudes. This altitude-climbing effect has ultimately resulted in an approximate loss of millions of flowers.
The findings paint a telling picture: hotter summers caused bumblebees' choice flower species to disappear, forcing them to evolve shorter tongues to tap into the remaining food sources. Then, competition with generalist species, more time and energy needed and a forced reliance on alternative sources all likely contributed to the bees' overall decline.
1. What was the cause of bumblebees' tongues shortening in Colorado?| A．Decrease of certain flowers. | B．Fight within populations. |
| C．The pollution of their food. | D．Common growth problems. |
| A．Clear results were published. | B．It was based on assumptions. |
| C．It was carried out for decades. | D．It intended to study bee diseases. |
| A．For more sunlight. | B．For cooler environment. |
| C．For more growing space. | D．For defence against insects. |
| A．A research on bees' tongues. | B．Facts and causes of bees' decline. |
| C．The relation of flowers and bees. | D．The climate influence on mutualism. |
