Tuesday, April 10, 2012

The good, the bad and the noisy

I thought I would take a break from the complicated molecular pathways for a week and do an ecology paper.  It was interesting to read an ecology paper because it was written in a totally different style.  I made it half way through the methods section before I realized it wasn’t the results section.  The paper is by Francis et al. and was published in the Proceedings of the Royal Society B (what royal society?  B for Biology?  I think so).

The authors were looking at the effects of noise pollution on an ecological system.  Many papers have examined how increased noise can affect the behaviors of individual species, but this paper focuses on how changes in one species can alter the ecosystem.  The results are not surprising at all, but what I found most interesting were the methods.  There were two main experiments: one looking at hummingbirds and pollination, the other examining seed dispersal by scrub jays.

Noise increases pollination
Turns out hummingbirds like noise.  This may seem surprising at first, but lets think about it.  Have you ever heard a hummingbird sing?  Vocalization doesn’t seem to be that important to them, so from their perspective, noisy areas are good because it drives away their competitors and predators.  Since hummingbirds are important pollinators, it goes to reason that a noisy area would attract more hummingbirds, which would pollinate more flowers, leading to an increased population and diversity of flowering plants. 

How do the authors actually test this, though?  For all their experiments, they went to New Mexico, which has natural gas wells.  Some of these wells are quiet and some of them have noisy compressors.  This provides a great experimental setting where the only variable is noise, because the type of human activity and the vegetation features are nearly the same at all the wells.  In order to measure how often flowers are visited by hummingbirds and if pollination has occurred, the authors set up some artificial flowers.  In this way, they can control for random variations in flowers at the noisy wells versus the quiet wells.  From what I gathered from their description, they used pipettes filled with sweet nectar that was replenished each day.  They “decorated” the pipettes with colored tape to imitate the colors of flowers.  Yarn and colored tape?  That sounds fun!  The hummingbirds totally fell for it and started visiting the artificial flowers.  As expected, the hummingbirds went to the flowers near the noisy wells more often than the quiet control wells.

When hummingbirds visit flowers, some of the pollen (containing sperm) brushes off onto their bodies.  As they fly to a new flower, they bring the pollen with them, which may fall off onto the female parts of another flower, thus completing pollination.  To test if the increased visits to noisy wells would lead to more pollination, the researchers put fluorescent dyes onto some of the artificial flowers.  They followed the transfer of the dyes between different flower patches, and found that near noisy wells, more of the dye was transferred from flower to flower.  In other words, there would most likely be an increase in pollination of these flowers near noisy areas. 

Noise impairs seed dispersal
Many trees depend on animals to carry their seeds away to new environments where they can germinate.  For this experiment, the authors focused on the seeds of the pine Pinus edulis.

The authors scattered seeds under pine trees and set up motion-triggered cameras.  Every time a seed was removed, a photo of the culprit was taken.  They found that one species of mice preferentially took seeds from trees near the noisy wells.  The mice probably like noisy areas for the same reason as hummingbirds: less predators around (like owls).  Unfortunately for the pine, the mice mostly ate the seeds and didn’t help disperse them.  On the other hand, scrub jays collect lots of seeds, hide them and then forget about them; this is the optimal situation for the pine seeds, because they don’t get eaten and they get to grow in new places.  Scrub jays, unlike the mice, avoid the noisy wells, probably because they rely a lot on vocal communication.  The unhelpful mice are more prominent at noisy wells and the helpful jays avoid the noisy wells, so all this leads to decreased seed dispersal and fewer pine seedlings growing near the noisy areas.

Changes in the number of the hummingbird-pollinated flowers (positively) and pine seedlings (negatively) can have all sorts of other effects on the ecosystem near noisy wells.  As we all expected, noise may only affect one species directly, but it can have long reaching consequences for all the integral members of the environment.  Bad news in our industrial world.

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