Smaller habitats worse than expected for biodiversity
New international research breaks ground for the next generation of biodiversity forecasts

Date:
July 29, 2020
Source:
German Centre for Integrative Biodiversity Research (iDiv)
Halle-Jena- Leipzig
Summary:
Biodiversity's ongoing global decline has prompted policies
to protect and restore habitats to minimize animal and plant
extinctions. However, biodiversity forecasts used to inform these
policies are usually based on assumptions of a simple theoretical
model describing how the number of species changes with the
amount of habitat. A new study shows that the application of
this theoretical model underestimates how many species go locally
extinct when habitats are lost.



FULL STORY ========================================================================== Biodiversity's ongoing global decline has prompted policies to protect
and restore habitats to minimize animal and plant extinctions. However, biodiversity forecasts used to inform these policies are usually based
on assumptions of a simple theoretical model describing how the number
of species changes with the amount of habitat. A new study published
in the journal Nature shows that the application of this theoretical
model underestimates how many species go locally extinct when habitats
are lost. Scientists from the German Centre for Integrative Biodiversity Research (iDiv), Martin Luther University Halle-Wittenberg (MLU) and the Helmholtz Centre for Environmental Research (UFZ) used data from 123
studies from across the world to set the path for the next generation
of biodiversity forecasts in the face of habitat loss and restoration.


==========================================================================
One of the most fundamental theories in biodiversity science describes
how the number of species increases as the area of habitat increases; conversely, as habitat is destroyed, species are lost. This theory allows ecologists to predict how many species will go extinct as humans destroy natural habitats, and how many species will be protected when habitats
are protected. There is a potential flaw, however, in how the theory is
applied to biodiversity forecasts.

'Ecosystem decay' refers to the case when some species are more likely
to go extinct when habitat is lost than predicted by theory. Pioneering conservation biologist, Thomas Lovejoy, coined the term to describe
results from studies in small forest islands left behind after
clearcutting in the Brazilian Amazon.

High levels of sunlight encroached into the normally dark forest
understory, harming plants adapted to lowlight conditions. Larger animals,
like monkeys and big cats, left or went locally extinct.

A global analysis Using rigorous statistical tools and a database of 123 studies of habitat islands from across the world, Prof Dr Jonathan Chase,
head of the Biodiversity Synthesis research group at iDiv and professor
at MLU, and colleagues provide conclusive evidence that ecosystem decay
is pervasive and point to a way to develop more realistic biodiversity forecasting models. Specifically, the scientists found fewer individuals,
fewer species, and less even communities in samples taken from a small
habitat compared to samples of the same size and effort taken from a
larger habitat.

Jonathan Chase said: "Mathematical models that are used for biodiversity forecasts typically ignore the effects of ecosystem decay. This is
because we have not, until now, had systematic evidence for just how
strong its effects are across ecosystems and species groups." He added:
"This means that most forecasts underestimate how much biodiversity is
being lost as habitats are lost." The scientists spent years compiling
data from published habitat loss studies from across the world. These
included data from tropical forest islands left within agricultural
matrices of oil palm, coffee, chocolate and banana trees.

From islands in lakes that were created during the construction of dams
for hydroelectricity. And from nature reserves isolated within expanding agriculture and urbanization across the world. They included data from
studies on plants and a wide variety of animals, including birds, bats,
frogs and insects. In many cases, the data Chase and colleagues needed
weren't available in the published paper. "We often went back to the
authors of the studies. Many of them went above and beyond, digging up
old field notebooks and cracking long-expired versions of software and
hardware to get us what we needed for our analyses," said Chase.

Variation in the patterns While the overall effect of ecosystem decay
was clear, the scientists found some interesting variation in their
dataset. "The quality of the land between the habitat islands, which
we call the matrix, influenced just how strong the effect of ecosystem
decay was," said Dr Felix May, formerly from iDiv and now a senior
scientist at Freie Universita"t Berlin. May added: "When the matrix was
very distinct from the habitat islands, like in landscapes with intense agriculture or urbanization, ecosystem decay in the habitat islands was
quite intense. However, when the matrix was less hostile, like in bird-
and bee- friendly agriculture, we found fewer extinctions in the habitat islands." Another co-author, Prof Dr Tiffany Knight, from MLU, UFZ and
iDiv, added: "One surprise was that we found weaker ecosystem decay in
studies from Europe, where habitat loss often occurred many hundreds of
years ago, compared to studies from other places where losses occurred
more recently." Knight continued: "We expected the opposite, because
ecosystem decay is thought to emerge slowly as species go extinct. But
what we found is that different species replaced those that were lost."
A way forward The results of this new study could be seen as dire because
it concludes that many biodiversity loss forecasts are too optimistic. But
the authors prefer to see the brighter side. "What we have found is that
it is possible to make more realistic projections for how biodiversity
will be lost as habitats are lost," Chase said. He added: "This will
allow us to make more informed policies regarding habitat protection
and provides added incentives for restoring habitats to restore the biodiversity within."

========================================================================== Story Source: Materials provided by German_Centre_for_Integrative_Biodiversity_Research_
(iDiv)_Halle-Jena-Leipzig. Note: Content may be edited for style and
length.


========================================================================== Journal Reference:
1. Jonathan M. Chase, Shane A. Blowes, Tiffany M. Knight, Katharina
Gerstner, Felix May. Ecosystem decay exacerbates biodiversity loss
with habitat loss. Nature, 2020; DOI: 10.1038/s41586-020-2531-2 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/07/200729114822.htm

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