Chapter 3 Extinction © 2002 by Prentice Hall, Inc. Upper Saddle River, NJ 07458

#2Chapt. 03 Outline Rate of extinction Causes of extinction Risks confronted by endangered species Characteristics of species and their relationship to extinction

#3Chapt. 03 The Extinction Crisis Extinction –All individuals die without producing progeny Pseudoextinction –Species disappear over evolutionary time

#4Chapt. 03 The Extinction Crisis Pseudoextinction –Lineage transformed into separate lineages Fossil Record –Extinct species to living species – 1,000:1

#5Chapt. 03 Extinction Crisis (cont.) Fossil Record (cont.). –Average life span of a species – 4 million years –Average extinction rate – 2.5 species per year

#6Chapt. 03 Extinction Crisis Fossil Record –Total number of species over time – 10 million Biased fossil record –Favors successful, geographically wide-ranging species –Persist longer than the average

#7Chapt. 03 Extinction Crisis Biased fossil record (cont.) –Biased toward vertebrates and mollusks –Background extinction rates are probably higher than indicated in fossil record. Example Extinction rates 10 times higher than predicted by fossil record

#8Chapt. 03 Extinction Crisis –Background extinction rates are probably higher than indicated in fossil record (cont.). 1 every 50 years for birds living today

#9Chapt. 03 Extintion Crisis Present extinction rate much high than in the past or predicted. –Effects due to humans – Distant Past Correlation between human population growth and the number of extinctions (Figure 3.1)

#10Chapt. 03 Number of humans ( billions ) Birds Mammals Number of extinct species Year

#11Chapt. 03 Extinction Crisis Effects due to humans (cont.). –Large scale extinctions in North and South America coinciding with the arrival of humans (11 thousand years ago) North America lost 73% of its genera of large mammals

#12Chapt. 03 Extinction Crisis Effects due to humans (cont.). –Large scale extinctions in North and South America (cont.). South America lost 80% of its genera of large mammals

#13Chapt. 03 Extinction Crisis (cont.) Effects due to humans (cont.). –Large scale extinctions in Australia coinciding with the arrival of humans (13 thousand years ago) Lost nearly all of its large mammals, giant snakes, and reptiles Nearly half of its large flightless birds

#14Chapt. 03 Extinction Crisis (cont.) –Probable causes of these extinctions Hunting Some climate change

#15Chapt. 03 Extinction Crisis Effects due to humans – Recent Past –Devastating effects on islands Hawaii – 4 th and 5 th century Polynesians arrived –Exterminated 50 out of 100 species of endemic land birds.

#16Chapt. 03 Extinction Crisis –Devastating effects on islands (cont.) New Zealand – End of the 18 th century –Entire avian megafauna consisting of huge land birds was exterminated –Accomplished through hunting and habitat destruction

#17Chapt. 03 Extinction Crisis –Devastating effects on islands (cont.) Madagascar – last 1,500 years –Exterminated –Giant elephant bird, largest bird ever recorded –20 species of lemur, most larger than any surviving species –2 giant land tortoises

#18Chapt. 03 Patterns of Extinction Islands vs. continental areas (Table 3.1)

#19Chapt. 03

#20Chapt. 03 Patterns of Extinction –Reasons for differences in extinction rate Island species may consist of a single population –Single climatic event can lead to extinction

#21Chapt. 03 Patterns of Extinction –Reasons for differences in extinction rate (cont.) Island species may have evolved in the absence of terrestrial predators –Characteristics contributing to extinction »Flightlessness »Tameness »Reduced reproductive rates –Ex. Hawaii (Figure 3.2)

Percent endangered Habitat loss Exotic species Pollution Hunting Disease Continental U.S. birds Hawaiian Birds Continental U.S. plants Hawaiian plants

#23Chapt. 03 Patterns of Extinction Causes of extinction (Figure 3.3)

#24Chapt. 03 No cause assigned Introduced animals Habitat destruction Hunting Other causes 56% 17% 16% 10% 1%

#25Chapt. 03 Patterns of Extinction –Introduced species effects Competition –Not been shown to eliminate an entire species Predation –Rats, cats, and mongooses have accounted for at least 112 of 258 extinctions of birds on islands (43%).

#26Chapt. 03 Patterns of Extinction Introduced species effects (cont.) –Disease and parasitism Avain malaria in Hawaii accounted for the loss of 50% of the local Hawaiian bird species

#27Chapt. 03 Patterns of Extinction –Causes of Extinction (Cont.) Habitat destruction –A prime cause of extinction –Ex. Deforestation –Subtle alterations (e.g. pollution) have not yet been shown to cause extinction Direct exploitation – Hunting –Caused numerous extinctions –Ex. Figure 3.4

#28Chapt. 03 Endangered Species Definition – a species that is thought to be at risk of extinction in the foreseeable future. Factors threatening species with Extinction –Habitat loss or modification

#29Chapt. 03 Endangered Species Factors threatening species with Extinction (cont.). –Hunting –Accidental or deliberate introduction of exotic species –Deliberate eradication

#30Chapt. 03 Endangered Species Factors threatening species with Extinction (cont.). –Incidental –Disease, both exotic and endemic

#31Chapt. 03 Endangered Species Characteristics of Factors –Human in origin –Species are threatened with several factors simultaneously –Relative importance as measured by frequency of occurrence

#32Chapt. 03 Endangered Species Characteristics of Factors (cont.) –Ex. Threats facing terrestrial mammals in Australia and the Americas 119 species considered endangered 75% threatened by more than one factor 27 species face four or more threats Major threat – 76% of the species are experiencing habitat loss or modification Figure 3.5

Threat and classes of threatsPercent of species affected Habitat loss & modification: 76% Cultivation & settlement Pastoral development Logging & plantations Other Exploitation: 50% Meat Fur and hides Live trade Predators Competitors Limited distribution Persecution Disturbance Incidental take Disease Introductions: 18% Others

#34Chapt. 03 Endangered Species Significance of hunting – Valuable fur and wood (Figure 3.6) Overexploitation –Overharvesting for commercial interests

#35Chapt. 03 Endangered Species Overexploitation (cont.). 1998, –Rare plants are threatened by collectors David Wilcove categorized threats to plants and animals in the US –Five categories

#36Chapt. 03 Endangered Species –Five categories (cont.) Habitat destruction Alien species Overharvesting Disease (both native and alien) Pollution

#37Chapt. 03 Endangered Species –Sample size: 1880 species –Results (Figure 3.7)

All species Percent of species threatened Habitat lossExotic speciesPollutionOver exploitationDisease Invertebrates Vertebrates Plants Mammals Birds Reptiles Amphibians Fish Freshwater mussels Butterflies Other invertebrates

#39Chapt. 03 Endangered Species Categorization of threats by class of species (Figure 3.8)

#40Chapt. 03 Percentage endangered Mammals Fish Birds Reptiles Amphibians All invertebrates

#41Chapt. 03 Endangered Species Categorization of threats by geographic areas (Table 3.2)

#42Chapt. 03

#43Chapt. 03 Endangered Species –The majority of threatened mammals occur in tropical countries Tropical countries have more species (therefore should have more endangered species Tropical countries have a higher percentage of endangered species as well.

#44Chapt. 03 Endangered Species (cont.) –Bigger countries have more endangered species than smaller countries (Figure 3.9)

#45Chapt Number of threatened mammals 10,00020,00050,000100, , ,0001,000,0002,000,000 Madagascar Indonesia India Brazil China Australia Zaire United States Argentina Mexico South Africa Nigeria Thailand Laos Vietnam Cameroon Tanzania Peru Colombia Country area (1000 ha)

#46Chapt. 03 Endangered Species (cont.) –US and endangered reptiles, amphibians, and fishes Better monitoring and documenting activities

#47Chapt. 03 Endangered Species Correlations between human factors and extinction –1995, Kerr and Currie Compared 90 countries –Six indices of human activities (Table 3.3)

#48Chapt. 03

#49Chapt. 03 Endangered Species (cont.) Correlation between human factors and extinction (cont.) Human population explained the most variation in the proportion of endangered species of birds. Per capita GNP explained the most variation in mammals

#50Chapt. 03 Species Characteristics and Extinction Rarity (Fig. 3.10) –Determined by Geographic range, Breadth of habitat Local population size Ability to disperse (Fig. 3.10)

#51Chapt. 03 Species Characteristics and Extinction (cont.) –Rescuing a population through immigration Degree of specialization (Fig. 3.10)

#52Chapt. 03 Species Characteristics and Extinction (cont.) Degree of specialization (cont.) –Organisms that are specialized are more likely to become extinct Limited food Limited habitat

Rare Common Poor dispersal Good dispersal Habitat destroyed More prone to extinction Less prone to extinction NN t t Can reach new fragment Not able to reach new fragment High specializationLow specialization Habitat fragments 3) Degree of specialization 2) Dispersal ability 1) Rarity

#54Chapt. 03 Species Characteristics and Extinction (cont.) Population variability (Fig. 3.10) –Stable populations are less likely to go extinct Trophic status (Fig. 3.10) –Applies to animals only –Higher trophic levels more at risk

#55Chapt. 03 Sudden population decline can lead to extinction Population size relatively constant: extinction unlikely Pyramid of numbers High trophic status NN t t Low trophic status More prone to extinctionLess prone to extinction Low variability High variability 4) Population variability 5) Trophic status Plants - thousands Herbivores - hundreds Carnivores - tens Top carnivores are very few, so prone to extinction as in 1

#56Chapt. 03 Species Characteristics and extinction (cont.) Life span (Fig. 3.10) Reproductive ability (Fig. 3.10)

#57Chapt. 03 More prone to extinctionLess prone to extinction 6) Life span Short life span Long life span 7) Reproductive ability High reproductive abilityLow reproductive ability

#58Chapt. 03 Summary Important causes of extinction –Introduced species (39%) –Habitat destruction (36%) –Direct exploitation (23%)

#59Chapt. 03 Summary (cont.) Factors threatening species –Habitat destruction Deforestation and ecosystem conversion

#60Chapt. 03 Summary (cont.) Species characteristics affecting the sensitivity to extinction –Rarity –Ability to Disperse –Degree of Specialization –Population variability

#61Chapt. 03 Summary Species characteristics affecting the sensitivity to extinction (cont.) –Trophic Status –Longevity –Reproductive ability

#62Chapt. 03 Discussion Question #1 Which type of organisms do you think deserve priority in conservation efforts and why?

#63Chapt. 03 Discussion Question #2 What ecological information would you need in order to list a species as endangered?

#64Chapt. 03 Discussion Question #3 If we are concerned with protecting rare species, should we also be concerned with protecting subspecies (or races) or even individual populations? Discuss the pros and cons of this issue.