threatened than birds (17%), with mammals and
reptiles experiencing intermediate threat levels (27).
Although defaunation is a global pattern,
geographic distribution patterns are also de-
cidedly nonrandom (28). In our evaluation of
mammals (1437 species) and birds (4263 spe-
cies), the number of species per 10,000 km2 in
decline (IUCN population status “decreasing”)
varied across regions from a few to 75 in mam-
mals and 125 in birds (Fig. 2), with highest
numbers in tropical regions. These trends per-
sist even after factoring in the greater species
diversity of the tropics (29, 30). Similarly, most
of 177 mammal species have lost more than 50%
of their range (9).
The use of statistical models based on life his-
tory characteristics (traits) has gained traction as
a way to understand patterns of biodiversity loss
(31). For many vertebrates, and a few inverte-
brates, there has been excellent research exam-
ining the extent to which such characteristics
correlate with threat status and extinction risk
(32–34). For example, small geographic range
size, low reproductive rates, large home range
size, and large body size recur across many studies
and diverse taxa as key predictors of extinction
risk, at least among vertebrates. However, these
“extinction models” have made little impact on
conservation management, in part because trait
correlations are often idiosyncratic and context-
dependent (31).
We are increasingly aware that trait correlations are generally weaker at the population level
than at the global scale (31, 35). Similarly, we now
recognize that extinction risk is often a synergistic
function of both intrinsic species traits and the
nature of threat (32, 34–37). For example, large
body size is more important for predicting risk in
island birds than mainland birds (34) and for
402 25 JULY 2014 • VOL 345 ISSUE 6195
sciencemag.org SCIENCE
Fig. 1. Evidence of declines in invertebrate abundance. (A) Of all insects with IUCN-documented
population trends, 33% are declining, with strong
variation among orders (19). (B) Trends among UK
insects (with colors indicating percent decrease
over 40 years) show 30 to 60% of species per order
have declining ranges (19). (C) Globally, a compiled index of all invertebrate population declines
over the past 40 years shows an overall 45% decline, although decline for Lepidoptera is less severe
than for other taxa (19). (D) A meta-analysis of
effects of anthropogenic disturbance on Lepidoptera,
the best-studied invertebrate taxon, shows considerable overall declines in diversity (19).
A
Percent of insect species
100
80
B
Percent decrease over 40 years
C
Global index of invertebrate abundance
D
Efects of disturbance on Lepidoptera
50
25
0
60
Col Hym Lep
Order Order
Odo Orth Col Hym Lep Odo
40
20
0
1970
0 4 -4
0.0
1.0
1.5
0.5
1980 1990
Diversity lower in
disturbed areas
Diversity higher in
disturbed areas 2000 2010
Stable
Increasing
Decreasing
All other invertebrates
Overall efect
> 0%
> 10%
> 20%
> 30%
> 40%
Lepidoptera
Fig. 2. Global population declines in mammals
and birds. The number of species defined by IUCN
as currently experiencing decline, represented in
numbers of individuals per 10,000 km2 for mammals and birds, shows profound impacts of defaunation across the globe.
