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Damage of tropical forests by insects decreases as warming progresses
Summary: Damage to woody plant’s foliage caused by insects significantly decreased
during the past 50 years in tropical forests, but remained unchanged in temperate forests.
Insect herbivory affects the productivity of ecosystems, modifies nutrient cycling, maintains
the diversity of plant communities and influences a number of ecosystem services. The
existing scenarios generally predict that increasing temperature will cause faster increases in
herbivory than in plant productivity, i.e. forest damage may be expected to increase as the
climate warms.
The analysis of the data published during the past 50 years provided no support for the
hypothesis proposing an increase in the background herbivory (i.e. in losses that occur when
insect populations are at their ‘normal’ densities, in contrast to occasional outbreaks of
eruptive species) with global environmental changes. Instead, we detected no temporal trend
in damage to woody plant’s foliage caused by insects within the temperate climate zone from
1952 to 2013, and a significant decrease in this damage in the tropics. From 1964 to 1990,
insect herbivory in the tropics was 39% higher than in the temperate region, but these
differences disappeared by the beginning of the 2000s.
We attribute the decrease in damage of tropical forests by insects to adverse effects of
increasing temperature, because fitness of insects declines sharply under temperatures beyond
the thermal optimum. Insects in the tropics are currently living very close to their optimal
temperatures; thus, even relatively minor temperature increases may have detrimental effects.
The observed absence of temporal trends in herbivory within the temperate zone can be
explained by a broad thermal tolerance of insect species living in this zone, which results in
their lower sensitivity to climate warming compared to tropical species.
Thus, environmental changes have already disturbed one of the global ecological patterns—
the decrease in herbivory with latitude—by affecting ecosystem processes differently in
tropical and temperate climate zones.
Reference: Kozlov, M. V. & Zvereva, E. L. (2015). Changes in the background losses of
woody plant foliage to insects during the past 60 years: are the predictions fulfilled? Biology
Letters, 11, 20150480 (doi: 10.1098/rsbl.2015.0480).
Link to the publisher's web site:
http://rsbl.royalsocietypublishing.org/content/11/7/20150480