Introduction

Over the last few centuries, as the human population has grown and disproportionately increased its use of resources, many species have lost their habitats through direct destruction or through changes in their biological or physical properties.

These changes have precipitated a major increase in the rate of species extinctions and loss of diversity. The 2021 analysis of the Red List of Threatened Species, compiled by the International Union for Conservation of Nature and Natural Resources (IUCN), estimates that 41,459 species are threatened with extinction—28% of the species that have been evaluated and almost 2% of all described species worldwide (TABLE 23.1). This number is certainly an underestimate, as only 7% of the species that have been described have been evaluated, and many species have yet to be taxonomically described.

TABLE 23.1 Global Summary of the Number of Documented Imperiled Species

Group	Estimated number of described species	Number of species evaluated by 2022	Number of threatened species by 2022	Estimated percentage of species threatened in 2022
Vertebrates
Mammals	6,577	5,969	1,337	26%
Birds	11,162	11,162	1,409	13%
Reptiles	11,690	10,150	1,845	21%
Amphibians	8,463	7,316	2,515	41%

Fishes	36,248	24,356	3,548	*
Subtotal	74,140	58,953	10,654
Invertebrates
Insects	1,053,578	12,161	2,291	*
Molluscs	84,528	9,017	2,384	*
Crustaceans	80,122	3,197	745	_*
Corals	5,574	846	232	_*
Arachnids	110,615	441	251	_*
Velvet worms	210	11	9	_*
Horseshoe crabs	4	4	2	100%
Others	157,543	904	152	_*
Subtotal	1,492,174	26,581	6,066
Plants
Mosses	21,925	282	165	_*
Ferns and allies	11,800	747	288	_*
Gymnosperms	1,113	1,046	436	42%
Flowering plants	369,000	59,222	23,551	_*
Green algae	12,382	16	0	_*
Red algae	7,480	58	9	_*
Subtotal	433,700	61,371	24,449
Fungi & Protists
Lichens	17,000	86	62	_*

Mushrooms, etc.	120,000	511	222	*
Brown algae	4,485	15	6	*
Subtotal	141,485	612	290	*
Total	2,131,499	147,517	41,459

Source: IUCN. 2022.

Summary Statistics Table 1a. In: The IUCN Red List of Threatened Species. Version 2022-1. >⅛⅝ https://www.iucnredlist.org/resources/summary-statistics. Downloaded on September 5, 2022. Note: “Imperiled” includes the IUCN Red List categories “critically endangered,” “endangered,” and “vulnerable.” Some groups have been more thoroughly evaluated (mammals, birds) for conservation status than other groups, for which only a small percentage of described species have been evaluated. For those groups, there may be a bias toward completing assessments of imperiled species and making assessments of more common species a lower priority, and thus the estimate of the percent of species is not included. That only 1% of described species are shown as imperiled is an artifact of incomplete evaluation, as the percentage is believed to be much higher. An asterisk (*) indicates insufficient coverage for accurate estimate.

Ecologists play an important role in measuring the losses of species and their underlying causes. As we'll see in this chapter and the next, ecologists are also one part of a diverse team working to find ways to slow the decline of species and their habitats. We'll begin by introducing you to the field of biology dedicated to reversing those declines: conservation biology.

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Source: Bowman W., Hacker S.. Ecology. 6th ed. — Oxford University Press,2023. — 744 p.. 2023

Introduction

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