onto ecosystem functioning and human well-being. Much remains unknown about 28 this "Anthropocene defaunation"; these knowledge gaps hinder our capacity to 29 predict and limit defaunation impacts. Clearly, however, defaunation is both a 30 pervasive component of the planet's sixth mass extinction, and also a major driver of 31 global ecological change. 32 33In the past 500 years, humans have triggered a wave of extinction, threat, and local 34 population declines that may be comparable in both rate and magnitude to the five 35 previous mass extinctions of Earth's history (1). Similar to other mass extinction events, 36 the effects of this "sixth extinction wave" extend across taxonomic groups, but are also 37 selective, with some taxonomic groups and regions being particularly affected (2). Here, 38we review the patterns and consequences of contemporary anthropogenic impact on 39 terrestrial animals. We aim to portray the scope and nature of declines of both species and 40 abundance of individuals, and examine the consequences of these declines. So profound 41 is this problem, that we have applied the term defaunation to describe it. This recent pulse 42 of animal loss, hereafter referred to as the Anthropocene defaunation, is not only a 43 conspicuous consequence of human impacts on the planet, but also a primary driver of 44 global environmental change in its own right. In comparison, we highlight the profound 45 ecological impacts of the much more limited extinctions, predominantly of larger 46vertebrates, that occurred during the end of the last Ice Age. These extinctions altered 47 ecosystem processes and disturbance regimes at continental scales, triggering cascades of 48 extinction thought to still reverberate today (3, 4). 49The term defaunation, used to denote the loss of both species and populations of 50 wildlife (5), as well as local declines in abundance of individuals, needs to be considered 51 in the same sense as deforestation, a term that is now readily recognized and influential in 52 focusing scientific and general public attention on biodiversity issues (5). However, 53 whilst remote sensing technology provides rigorous quantitative information and 54 compelling images of the magnitude, rapidity and extent of patterns of deforestation, 55 defaunation remains a largely cryptic phenomenon. It can occur even in large protected 56 habitats (6) and, yet, some animal species are able to persist in highly modified habitats, 57 making it difficult to quantify without intensive surveys. 58Analyses of the impacts of global biodiversity loss typically base their 59 conclusions on data derived from species extinctions (1, 7, 8) and typically evaluations of 60 the effects of biodiversity loss draw heavily from small scale manipulations of plants and 61 small sedentary consumers (9). Both of these approaches likely underestimate the full 62 impacts of biodiversity loss. While species extinctions are of great evolutionary 63 significance, declines in the number of individuals in local populations and chan...

The collapsing populations of large herbivores will have extensive ecological and social consequences.

Local extinctions have cascading effects on ecosystem functions, yet little is known about the potential for the rapid evolutionary change of species in human-modified scenarios. We show that the functional extinction of large-gape seed dispersers in the Brazilian Atlantic forest is associated with the consistent reduction of the seed size of a keystone palm species. Among 22 palm populations, areas deprived of large avian frugivores for several decades present smaller seeds than nondefaunated forests, with negative consequences for palm regeneration. Coalescence and phenotypic selection models indicate that seed size reduction most likely occurred within the past 100 years, associated with human-driven fragmentation. The fast-paced defaunation of large vertebrates is most likely causing unprecedented changes in the evolutionary trajectories and community composition of tropical forests.

Summary1. The effects of the present biodiversity crisis have been largely focused on the loss of species. However, a missed component of biodiversity loss that often accompanies or even precedes species disappearance is the extinction of ecological interactions. 2. Here, we propose a novel model that (i) relates the diversity of both species and interactions along a gradient of environmental deterioration and (ii) explores how the rate of loss of ecological functions, and consequently of ecosystem services, can be accelerated or restrained depending on how the rate of species loss covaries with the rate of interactions loss. 3. We find that the loss of species and interactions are decoupled, such that ecological interactions are often lost at a higher rate. This implies that the loss of ecological interactions may occur well before species disappearance, affecting species functionality and ecosystems services at a faster rate than species extinctions. We provide a number of empirical case studies illustrating these points. 4. Our approach emphasizes the importance of focusing on species interactions as the major biodiversity component from which the 'health' of ecosystems depends.

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Trophic rewilding is an ecological restoration strategy that uses species introductions to restore top-down trophic interactions and associated trophic cascades to promote self-regulating biodiverse ecosystems. Given the importance of large animals in trophic cascades and their widespread losses and resulting trophic downgrading, it often focuses on restoring functional megafaunas. Trophic rewilding is increasingly being implemented for conservation, but remains controversial. Here, we provide a synthesis of its current scientific basis, highlighting trophic cascades as the key conceptual framework, discussing the main lessons learned from ongoing rewilding projects, systematically reviewing the current literature, and highlighting unintentional rewilding and spontaneous wildlife comebacks as underused sources of information. Together, these lines of evidence show that trophic cascades may be restored via species reintroductions and ecological replacements. It is clear, however, that megafauna effects may be affected by poorly understood trophic complexity effects and interactions with landscape settings, human activities, and other factors. Unfortunately, empirical research on trophic rewilding is still rare, fragmented, and geographically biased, with the literature dominated by essays and opinion pieces. We highlight the need for applied programs to include hypothesis testing and science-based monitoring, and outline priorities for future research, notably assessing the role of trophic complexity, interplay with landscape settings, land use, and climate change, as well as developing the global scope for rewilding and tools to optimize benefits and reduce human-wildlife conflicts. Finally, we recommend developing a decision framework for species selection, building on functional and phylogenetic information and with attention to the potential contribution from synthetic biology.conservation | megafauna | reintroduction | restoration | trophic cascades

BackgroundSome neotropical, fleshy-fruited plants have fruits structurally similar to paleotropical fruits dispersed by megafauna (mammals >103 kg), yet these dispersers were extinct in South America 10–15 Kyr BP. Anachronic dispersal systems are best explained by interactions with extinct animals and show impaired dispersal resulting in altered seed dispersal dynamics.Methodology/Principal FindingsWe introduce an operational definition of megafaunal fruits and perform a comparative analysis of 103 Neotropical fruit species fitting this dispersal mode. We define two megafaunal fruit types based on previous analyses of elephant fruits: fruits 4–10 cm in diameter with up to five large seeds, and fruits >10 cm diameter with numerous small seeds. Megafaunal fruits are well represented in unrelated families such as Sapotaceae, Fabaceae, Solanaceae, Apocynaceae, Malvaceae, Caryocaraceae, and Arecaceae and combine an overbuilt design (large fruit mass and size) with either a single or few (<3 seeds) extremely large seeds or many small seeds (usually >100 seeds). Within-family and within-genus contrasts between megafaunal and non-megafaunal groups of species indicate a marked difference in fruit diameter and fruit mass but less so for individual seed mass, with a significant trend for megafaunal fruits to have larger seeds and seediness.Conclusions/SignificanceMegafaunal fruits allow plants to circumvent the trade-off between seed size and dispersal by relying on frugivores able to disperse enormous seed loads over long-distances. Present-day seed dispersal by scatter-hoarding rodents, introduced livestock, runoff, flooding, gravity, and human-mediated dispersal allowed survival of megafauna-dependent fruit species after extinction of the major seed dispersers. Megafauna extinction had several potential consequences, such as a scale shift reducing the seed dispersal distances, increasingly clumped spatial patterns, reduced geographic ranges and limited genetic variation and increased among-population structuring. These effects could be extended to other plant species dispersed by large vertebrates in present-day, defaunated communities.

Biodiversity is essential to human well-being, but people have been reducing biodiversity throughout human history. Loss of species and degradation of ecosystems are likely to further accelerate in the coming years. Our understanding of this crisis is now clear, and world leaders have pledged to avert it. Nonetheless, global goals to reduce the rate of biodiversity loss have mostly not been achieved. However, many examples of conservation success show that losses can be halted and even reversed. Building on these lessons to turn the tide of biodiversity loss will require bold and innovative action to transform historical relationships between human populations and nature.