Importance of rainfall highlighted for tropical animals

Date:
August 25, 2020
Source:
University of Illinois College of Agricultural, Consumer and
Environmental Sciences
Summary:
Imagine a tropical forest, and you might conjure up tall trees
hung with vines, brightly colored birds, howling monkeys, and
... rain. Indeed, precipitation patterns, along with temperature,
dictate where tropical forests are distributed around the world,
but surprisingly, scientists know very little about the direct
effects of rainfall on animals. A new conceptual framework calls
for the scientific community to formally consider the role of
precipitation in an organism's ecological niche.



FULL STORY ========================================================================== Imagine a tropical forest and you might conjure up tall trees hung with
vines, brightly colored birds, howling monkeys, and ... rain. Indeed, precipitation patterns, along with temperature, dictate where tropical
forests are distributed around the world, but surprisingly, scientists
know very little about the direct effects of rainfall on animals.


==========================================================================
A new conceptual framework, developed by University of Illinois and
Kansas State University researchers, calls for the scientific community to formally consider the role of precipitation in an organism's ecological
niche -- the set of biological and environmental factors that optimize
life for a given critter.

"We understand exactly how most animals respond to temperature, but the
same is not true for rain," says Alice Boyle, associate professor in
the Division of Biology at Kansas State and lead author on the Trends
in Ecology & Evolution article. "When animal biologists see rainfall
effects in their studies, they assume it must be about how plants
are responding to rainfall and how that affects the food supply for
the organisms they're studying. But there can be direct physiological consequences of rain related to feeding behavior, predation, pathogens,
and more. There's a lot more going on than food supply." In the article,
Boyle and co-authors Elsie Shogren and Jeff Brawn propose and define what
they call the hygric niche: the collection of physiological, behavioral,
and ecological processes and interactions predicting how endothermic,
or warm-blooded, organisms perform under a given precipitation scenario.

"Prior to this, there was no unifying conceptual framework to understand
why responses to precipitation might differ between species or even
within the same species, depending on the location of the study," Boyle
says. "We've heard from scientists who have said, 'Wow, how come I've
never thought about this before?' I think this new framework is probably
going to change the way many people study the distributions, physiology,
and demographic responses of endotherms." Brawn, professor in the
Department of Natural Resources and Environmental Sciences at Illinois,
adds, "This concept has implications for conservation of sensitive
organisms, long term. In terms of planning where to invest conservation
dollars or where to prioritize habitat, we should be looking at rainfall refugia where precipitation regimes are likely to stay intact over time." Because the effects of temperature and moisture are so difficult to disentangle, the team developed the concept of the hygric niche using
decades of bird and mammal research from the tropics. Temperature
in these equatorial landscapes varies little on an annual basis, but
rainfall can vary widely, with some locations experiencing distinct dry
and wet seasons and others experiencing daily precipitation throughout the year. But unfortunately, in many tropical locations, these millennia-old patterns are now shifting due to climate and land use change.



========================================================================== "Human-caused changes to climate are resulting in some areas getting
wetter, and other areas getting drier. Also, it is not just the amount
of precipitation that is changing; the timing and magnitude of storms
are also changing, and we have very little idea of how any of this will
affect animals," according to the authors.

In their article, Brawn and Boyle describe ways in which precipitation
(too little or too much) can affect organisms at the individual,
population, and community levels. While rain clearly affects food supply,
it also can affect foraging behavior, reproductive and population growth
rates, and competitive interactions in subtle ways that might be difficult
for researchers to trace back to any particular source. And even small
shifts in tropical rainfall patterns could have large effects.

"Even if you can see intact forest out to the horizon, if the
precipitation regimes change, the integrity of that ecosystem may be compromised. And that's concerning," Brawn says.

Although the concept was conceived with tropical systems in mind,
the researchers suggest it can and should be applied to ecosystems and organisms outside the tropics, with a bit of tweaking and further study.

"I work in both tropical and grassland systems and my major focus of
research in grassland birds, one of the most threatened group of birds in
North America, is understanding how temporal variation in precipitation
affects those populations. So the questions and the concepts are
broadly applicable," Boyle says. "It's just that it was more tractable
to lay them out and argue for their importance in tropical systems."
Laying out a new ecological concept requires lots of testing by the
research community to identify its limitations, and that's just what
Boyle and Brawn hope will happen.



==========================================================================
"The next steps involve the research community testing key assumptions
and predictions of our model," they say. "One of the hardest but most
important tasks is to understand whether rainfall affects different animal species for the same or different reasons. Is it really mostly about
food, or are these less-obvious physiological costs more important than
we thought? Answering these questions will be crucial to doing effective conservation and climate change mitigation in the tropics." The work
was supported by the National Science Foundation (grant #1646806).

The Department of Natural Resources and Environmental Sciences is in
the College of Agricultural, Consumer and Environmental Sciences at the University of Illinois.


========================================================================== Story Source: Materials provided by University_of_Illinois_College_of_Agricultural,_Consumer and_Environmental_Sciences. Original written by Lauren Quinn. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. W. Alice Boyle, Elsie H. Shogren, Jeffrey D. Brawn. Hygric
Niches for
Tropical Endotherms. Trends in Ecology & Evolution, 2020; DOI:
10.1016/ j.tree.2020.06.011 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/08/200825121829.htm

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