Earth’s Seasonal Rhythms Are Changing, Putting Species And Ecosystems At Risk

Seasonality shapes much of life on Earth. Most species,
including
humans, have synchronised
their own rhythms with those of Earth’s
seasons.

Plant growth cycles, the migration of
billions of animals, and even aspects of human culture –
from harvest rituals to Japanese cherry blossom viewings –
are dictated by these dominant rhythms.

However,
climate change and many other human impacts are altering
Earth’s cycles. While humans can adapt their behaviour by
shifting
the timing of crop harvests or Indigenous fire-burning
practices, species are less able to adapt through
evolution or range shifts.

Our
new research highlights how the impacts of shifting
seasons can cascade through ecosystems, with widespread
repercussions that may be greater than previously
thought.

This puts species and ecosystems at risk the
world over. We are still far from having a full picture of
what changes in seasonality mean for the future of
biodiversity.

Almost every ecosystem on Earth has
seasons

From tropical forests to polar ice caps and
abyssal depths, the annual journey of Earth around the Sun
brings distinct seasons to all corners of the
planet.

These seasonal rhythms shape ecosystems
everywhere, whether through monsoonal rains in equatorial
regions or the predictable melt of snowpack in mountain
ranges.

But the seasonality of these processes is
changing rapidly due to local human impacts. This includes
dams in many rivers, which
completely and abruptly disrupt their natural flow, and
deforestation,
which changes the timing of the onset of the rain
season.

These local influences are compounded by
climate change, which is systematically modifying seasonal
patterns in snow cover, temperature
and rainfall
around the world.

From the earlier seasonal melting of
glaciers and the snowpack to the disruption of monsoonal
rain cycles, the effects of these changes are being felt
widely.

Many important ecological processes we rely on
could be affected. A mismatch
between plankton blooms and the life cycles of fish
could affect the health of fisheries. Tourism
dependent on seasonal migrations of large mammals could
suffer. Even the regulation
of the climate system itself is tightly controlled by
seasonal processes.

Changing seasonality threatens to
destabilise key ecological processes and human
society.

Evolutionary adaptations to seasonal
fluctuations

The seasonal rhythms of ecosystems are
obvious to any observer. The natural timing of annual
flowers and deciduous trees – tuned to match seasonal
variations in rainfall, temperature and solar radiation –
transforms the colours of whole landscapes throughout the
year.

The arrival and departure of migratory birds,
the life cycle of insects and amphibians, and the mating
rituals of large mammals can completely change the
soundscapes with the seasons.

These examples
illustrate how seasonality acts as a strong evolutionary
force that has shaped the life cycles and behaviour of most
species. But, in the face of unprecedented changes to
Earth’s natural rhythms, these adaptations can lead to
complex negative impacts.

For instance, snowshoe
hares change coat colour between winter and summer to
blend in with their surroundings and hide from predators.
They are struggling to adapt to shifts in the timing of the
first snow and snowmelt. The impact of changing seasonality
on hare populations is linked with changes in predation
rates. But predators themselves may also be out of sync with
the new onset of seasons.

Our research highlights that
these kinds of complex interactions can propagate impacts
through ecosystems, linking individual species’ seasonal
adaptations to broader food web dynamics, or even ecosystem
functions such as carbon sequestration.

Although
biologists have studied seasonal processes for centuries, we
know surprisingly little about how they mediate any
ecological impacts of altered seasonality. Our findings show
we are likely underestimating these impacts.

The
distinct mechanisms involved deserve further attention.
Until we account for these complex processes, we risk
overlooking important ecological and human
consequences.

The more we understand, the better
prepared we are

Understanding the extent to which
impacts of altered seasonality can interact and propagate
from individuals to whole ecosystems is a big challenge. It
will require different types of research, complex
mathematical modelling and the design of new experiments.
But it is not easy to manipulate the seasons in an
experiment.

Scientists have come up with inventive
ways of experimentally testing the effects of altered
seasonality. This includes manually
removing snow early in spring, manipulating
rainfall patterns through irrigation and moving
plants and animals to places with different
seasonality.

Some researchers have even recovered
seeds from centuries-old collections to sprout them and
look at how recent changes in climate have affected plant
populations.

These efforts will be of great value for
forecasting impacts and designing effective management
strategies beneficial for ecosystems and humans alike. Such
efforts help to anticipate future shocks and prioritise
interventions.

For instance, understanding the
mechanisms that allow native and non-native species to
anticipate seasonal changes has proven useful for “tricking”
non-native plants into sprouting only in the wrong season.
This gives an advantage to native plants.

Similarly,
studies
on the molecular mechanisms involved in the response to
seasonality can help us determine whether certain
species are likely to adapt to further changes in seasonal
patterns. This research can also point out genes that could
be targeted for improving the resilience and productivity of
crops.

Not only are we likely underestimating the
ecological risks of shifting seasons, we tend to forget how
much our everyday lives depend on them. As Earth’s rhythms
change, the risks multiply. But so does our opportunity to
better understand, anticipate and adapt to these
changes.

Daniel
Hernández Carrasco, PhD Candidate in Ecology,
University
of Canterbury and Jonathan
Tonkin, Associate Professor of Ecology and
Rutherford Discovery Fellow, University
of Canterbury

This article is republished
from The
Conversation under a Creative Commons license.
Read the original
article.

Disclosure
statement

Daniel Hernández Carrasco receives
funding from a Doctoral Scholarship by the University of
Canterbury.

Jonathan Tonkin receives funding
from a Rutherford Discovery Fellowship administered by the
Royal Society Te Apārangi and the Centres of Research
Excellence Bioprotection Aotearoa and Te Pūnaha
Matatini.

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