Figure 1.
IUCN Red List threat levels by geographic region.
a) Threat levels for vertebrate seed dispersers. b) Threat levels for vertebrate pollinators. Geographic regions are as provided in the IUCN Red List (www.iucnredlist.org). DD = Data Deficient. EW = Extinct in the Wild. CR = Critically Endangered. EN = Endangered. VU = Vulnerable. NT = Near Threatened. LC = Least Concern.
Figure 2.
PRISMA flowchart providing the steps of data collection for this systematic review.
Figure 3.
A review of pollinator exclusion studies yielded weighted mean seed set reductions for widows previously pollinated by different vertebrate classes.
a) Seed set reductions after bat exclusion for bat-pollinated plants. b) Seed set reductions after nonvolant mammal exclusion for nonvolant mammal-pollinated plants. c) Seed set reductions after bird exclusion for bird-pollinated plants. d) Seed set reductions after lizard exclusion for lizard-pollinated plants. Bars depict weighted means. Vertical lines represent standard error. The minimum seed set observed in any exclusion study is indicated with an asterisk (*); this is the minimum predicted effect of loss of vertebrate pollinators for a given plant species. Bold numbers at the top of each bar provide the number of independent publications used to calculate each weighted mean.
Table 1.
Constituent values used to estimate the number of plants likely to be widowed if currently threatened vertebrate species become extinct.
Table 2.
Average number of vertebrate partners per plant (P), proportion of vertebrate partners that are threatened with extinction (T), and proportion of total vertebrate-mutualist plants at risk of losing all vertebrate partners (TP), by geographic region.
Figure 4.
Existing widow plants demonstrate reduced reproduction, while threatened vertebrates suggest that many more species may become widowed, especially on islands.
a) The extinction of honeycreepers including (i) Hawaii's black mamo (Drepanis funerea) resulted in widowhood for lobelioids including (ii) Cyanea stictophylla [29]. The near extinction of (iii) New Zealand's greater short-tailed bat (Mystacina robusta) widowed (iv) Freycinetia baueriana [30]. The island-scale extinction of (v) the lizard Podarcis lilfordi in the Balearic Islands disrupted the pollination of (vi) Euphorbia dendroides [31]. b) IUCN conservation status rankings for vertebrate pollinators and dispersers reveal that island endemic species (red bars) are more vulnerable by percent threatened than are vertebrate mutualists globally (green bars). Photo/image credits: F. W. Frowahk (Drepanis funerea); C. Aslan (Cyanea stictophylla); B. Duperron (Mystacina robusta); Armchair Travel and Kew Gardens (Freycinetia baueriana); D. André (Podarcis lilfordi); K. Kozminski (Euphorbia dendroides).