ArticlePublisher preview available

Impacts of wildlife trade on terrestrial biodiversity

April 2021
Nature Ecology & Evolution 5(4):1-9

DOI:10.1038/s41559-021-01399-y

Authors:

Oscar Morton

University of Cambridge

Brett R Scheffers

University of Florida

Torbjørn Haugaasen

Norwegian University of Life Sciences

David P Edwards

University of Cambridge

The wildlife trade is worth billions of dollars annually and affects most major taxonomic groups. Despite this, a global understanding of the trade’s impacts on species populations is lacking. We performed a quantitative meta-analysis of the wildlife trade that synthesized 506 species-level effect sizes from 31 studies, estimating trade-driven declines in mammals (452 effect sizes), birds (36) and reptiles (18). Overall, species declined in abundance by 62% (95% confidence interval (CI), 20 to 82%) where trade occurs. Reductions involving national or international trade were greatest, driving declines of 76% (95% CI, 36 to 91%) and 66% (95% CI, 12 to 87%), respectively. The impacts of trade were pervasive, requiring over 102 hours of travel time from settlements for trade to have no mean effect. Current protective measures fail species, with significant declines even where the harvesting for trade occurs in protected areas. Population declines tracked species threat status, indicating heightened extirpation and extinction risk in traded species. Critically, for such a severe global threat to wildlife, our analysis unearthed a limited number of studies using treatment versus control comparisons, and no studies on amphibians, invertebrates, cacti or orchids. Improved management, tackling both unsustainable demand and trade reporting, must be a conservation priority to prevent rampant trade-induced declines.

Distribution of the data sources and the extracted effect sizes for birds, mammals and reptiles included in the meta-analysis a, Distribution of the 31 data sources. b, Distribution of the 506 extracted effect sizes. The shaded countries each contain at least one study, and the points denote the locations of individual study sites. Antarctica was removed from this graphic as no studies were present.

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Individual, class and purpose effect size estimates a, 506 taxon-wide effect size estimates showing the 95% CIs. Weighted mean population declines of 61.6% (95% CI, 20.0–81.6%) are shown by the red line, and the dashed black line denotes no impact of trade. Extremely negative results indicate local extirpations (population declines of 100%). b, Taxon-specific effect size estimates. c, Stated trade-purpose estimates of effect size. ‘Assorted’ includes ivory, traditional medicine and laboratory use. The points show the weighted means, and the lines show the 95% CIs. The estimates were obtained through single mixed meta-regressions.

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Effect of trade on species abundance with travel time to settlements (with a population greater than 5,000) a, Effect size estimates across levels of trade. The error bars correspond the estimates’ 95% CIs. b, The effect of travel time on species across all trade levels, from local to international. c–e, Effect sizes of travel time for local (c), national (d) and international trade (e). Extremely negative results indicate local extirpations (population declines of 100%). The points denote the raw effect sizes, the solid red line indicates the mean predicted effect size, the dotted red line is the model extrapolation and the black lines denote the 95% CIs. The point size corresponds to each effect’s sampling variance.

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Impact of trade on species conservation and protected area status a, Trade-induced population declines by International Union for Conservation of Nature (IUCN) threat status. Aggregated species effect sizes are excluded. LC, least concern; NT, near threatened; VU, vulnerable; EN, endangered; CR, critically endangered; DD, data deficient. b, Effect of internationally listed protected areas. WDPA, World Database on Protected Areas. c, Effect of local protection; see Methods for details on the classification. The points denote the mean weighted effect sizes, the lines indicate the corresponding 95% CIs and the dashed black lines indicate no impact of trade. The estimates were obtained through single mixed meta-regressions. Tukey’s HSD post hoc tests were used to assess differences within b and c.

…

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Articles

https://doi.org/10.1038/s41559-021-01399-y

1Department of Animal and Plant Sciences, University of Sheffield, Sheffield, UK. 2Department of Wildlife Ecology and Conservation, Institute of Food and

Agricultural Sciences, University of Florida, Gainesville, FL, USA. 3Faculty of Environmental Sciences and Natural Resource Management, Norwegian University

of Life Sciences, Ås, Norway. ✉e-mail: omorton1@sheffield.ac.uk; david.edwards@sheffield.ac.uk

The wildlife trade is a burgeoning global industry worth

US$4−20 billion per year1. This encompasses both regulated,

legal trade and poorly regulated, illegal trade, co-occurring

at local to international levels2–4. At least 100 million plants and

animals are internationally trafficked each year5, involving a hyper-

diversity of species6. For instance, 24% (N = 7,638) of terrestrial ver-

tebrate species, spanning 75% of terrestrial vertebrate families, have

recently been or are currently traded6. Understanding the drivers

and impacts of wildlife trade is therefore one of the key challenges

for modern conservation7.

Local-scale trade for both food and income security supports an

estimated 150 million rural households involved with the extrac-

tion or commercialization of bushmeat8. Conversely, the national

to international trade in pets, medicines and luxury meats often

involves a small number of highly specialized parties extracting

and trafficking species of high commercial value. At all scales, trade

has the potential to support livelihoods and even protect species

from extinction9,10, with sustainable trade potentially as lucrative as

unsustainable methods11. But at its worst, intensive extraction and

trade is a prominent driver of extinction risk and a global threat

to species12. This is demonstrated by the ivory-fuelled declines of

African elephants13, the killing of the last Javan rhinoceros of the

subspecies annamiticus for its horn in Vietnam in 2010 (ref. 14) and

the rapid demise of pangolin species across Asia and Africa15.

A quantitative global assessment of trade impacts on individual

species and the prevalence and strength of positive and negative

effects is sorely lacking. Studies inferring positive outcomes of trade

have synthesized evidence from secondary literature and market

trends to assess sustainability, but they generally have not directly

examined trade impacts on species abundances in the wild9,16,17.

Potentially positive results include the sustainable extraction and

trade of more tolerant species, although at the cost of less tolerant

species16. Those inferring negative outcomes of trade synthesized

evidence from multispecies market surveys, combining expert

opinion with market share trends, to infer population changes18.

Such studies suggest that the current volumes of animals traded are

unsustainable and probably contribute to species declines. However,

they can be confounded by pre-existing market trends19 and con-

current threats driving species losses, including deforestation,

subsistence hunting and climate change20–22.

Our study quantifies the impact of wildlife trade on species

abundances via a meta-analysis comparing traded sites with unex-

ploited, control sites. We answer three key questions: (1) what is

the impact of wildlife trade on species abundance, (2) how does

the impact of trade vary with spatial scale and access to markets,

and (3) how effective are current measures designed to protect spe-

cies? Without precise quantification of the effects of trade, policies

managing trade fail to be evidence-based and thus cannot claim to

safeguard species.

Results and discussion

Trade-induced impacts on species’ abundance. We performed a

systematic search of the primary and secondary literature for stud-

ies comparing the impact of wildlife trade between traded (treat-

ment) and untraded (control) sites on vertebrate, invertebrate,

orchid and cactus species abundance. We incorporated all forms

of wildlife trade, ranging from local to national and international

scales, and spanning both legal and illegal trade. From the suitable

studies (Supplementary Information), we extracted the location,

reported purpose, scale of trade, species abundance and associated

variance. We calculated effect sizes as the log response ratio (RR) of

the abundances in traded and untraded sites; for clarity in interpre-

tation, in the main text we present the RR as the percentage change

in abundance (see Methods). Our systematic search obtained 506

effect sizes (452 for mammals, 36 for birds and 18 for reptiles; no

suitable studies were found for other taxa) from 31 studies com-

paring the impact of wildlife trade between traded (treatment) and

untraded (control) sites (all using space-for-time substitution, none

using before–after comparisons; Fig. 1 and Supplementary Table 1).

We uncovered several alarming patterns in the geographic

coverage and taxonomic representation of studies using robust

methods to characterize abundance responses to trade. First, there

Impacts of wildlife trade on terrestrial biodiversity

Oscar Morton 1 ✉ , Brett R. Scheffers 2, Torbjørn Haugaasen 3 and David P. Edwards 1 ✉

The wildlife trade is worth billions of dollars annually and affects most major taxonomic groups. Despite this, a global under-

standing of the trade’s impacts on species populations is lacking. We performed a quantitative meta-analysis of the wildlife trade

that synthesized 506 species-level effect sizes from 31 studies, estimating trade-driven declines in mammals (452 effect sizes),

birds (36) and reptiles (18). Overall, species declined in abundance by 62% (95% confidence interval (CI), 20 to 82%) where

trade occurs. Reductions involving national or international trade were greatest, driving declines of 76% (95% CI, 36 to 91%)

and 66% (95% CI, 12 to 87%), respectively. The impacts of trade were pervasive, requiring over 102 hours of travel time from

settlements for trade to have no mean effect. Current protective measures fail species, with significant declines even where the

harvesting for trade occurs in protected areas. Population declines tracked species threat status, indicating heightened extirpa-

tion and extinction risk in traded species. Critically, for such a severe global threat to wildlife, our analysis unearthed a limited

number of studies using treatment versus control comparisons, and no studies on amphibians, invertebrates, cacti or orchids.

Improved management, tackling both unsustainable demand and trade reporting, must be a conservation priority to prevent

rampant trade-induced declines.

NATURE ECOLOGY & EVOLUTION | VOL 5 | APRIL 2021 | 540–548 | www.nature.com/natecolevol

540

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