Exam 2 Conservation Biology

Demographic causes of extinction

Variation in population size

• random variation in reproduction and death rates

  • species with highly variable birth and death rates

• small populations more susceptible to demographic fluctuations

• low birth rates

• uneven sex ratio

  • especially if their birth rate relies on uneven sex ratio

  • one male = some females will have no kin

Allee effect

Populations that fall below a certain “critical minimum” will have diminished survival and reproduction

• Group behaviors such as hunting and defense against predators become impossible

• Inadequate social cues for key behaviors

Allee example

African wild dogs are obligate group hunters

• They need to hunt in a pack

• The alpha pair will not reproduce if there isn’t enough members to raise the pups

Razor billed Auk

• There needs to be at least 7 individuals to initiate reproduction

• If below there is not enough social cue to reproduce

Musk Ox

• Protect young by facing outwards in packs

Environmental causes of extinction

Environmental stochasticity

• random changes in environmental conditions

• variation in predators, pathogens, and food

• fires, droughts, climate (regular cycle)

Catastrophe

• fires, droughts, climate (irregular cycle)

  • irregular fires from fire suppression

What is more important than random demographic variation in increasing the probability of extinction in small populations?

Environmental stochasticity

Lower effective population size = 

• More demographic variation

• Population more subdivided by fragmentation

• More imbreeding depression

• Less genetic variation

• Extinction

(Management Perspective) What is more valuable to understand than the factors that finally cause the extinction of a species?

The factors that cause a species to become imperiled

Living dead

Species or populations that are functionally extinct despite still having individuals

Extinction debt

A future loss of species due to past environmental impacts, like habitat destruction, that has not yet resulted in extinction

10:50 rule

If we preserve 10% of land, we preserve 50% of species

Primary human influences on living systems

• Habitat destruction

• Habitat fragmentation

• Habitat degradation (includes pollution)

• Global climate change

• Overexploitation

• Invasive species

• Disease

Habitat Destruction

Primary cause of biodiversity destruction

Threatened habitats

Tropical deciduous forests

• Converted for agriculture

Grasslands

• Converted for farm land and cattle ranching

Freshwater habitats

• Dams, channelization of watercourses, chemical pollution

• Ecosystem functions and services are lost

Marine coastal areas

• Invasive species, rising temperatures, sedimentation, pollution

Mangroves

• Important economically (commercial fisheries)

• Protection from storm surges

• Has a lot of dependent species that are at risk of extinction

Coral reefs

• 20% destroyed

• 20% degraded (over- fishing, harvesting, pollution, invasive species)

Arc of deforestation

Crescent-shaped region in the eastern and southeastern Amazon, primarily in Brazil, where deforestation rates are highest due to ranching, agriculture, and logging

• Tropical rainforests take up a small percent of surface area but take up most of the deforestation

Animals at risk due to palm oil production

• Norman Orangutan

• Sumatran Orangutan

• Sumatran Tiger

• Sumatran Rhino

• Borneo Elephant

Habitat fragmentation differs from original habitat in 3 ways

1. Greater amount of edge per area of habitat

2. The center is closer to an edge

3. Each fragment holds a smaller population

Edge influences

Invasive species, sun exposure, wind exposure, invasive species exposure, fire, drought

• As areas get smaller, more percent of the area will be exposed to an edge

Threats from Habitat Fragmentation

• Limits to dispersal and colonization

• Restricted access to food and mates

• Creation of smaller populations

  • Imbreeding depression, genetic drift

• Interspecies interactions

  • Wild and domestic animal interactions

• Edge effects

Habitat fragmentation example

Mountain lions

• Due to fragmentation, there have been isolated males that can’t find females, imbreeding, and smaller population sizes

Florida panther

• used to live in many states, but now is restricted to southern Florida

• intersected by highways that have been placed in the middle of the habitat

Pronghorn

• they will only go under fences, as they did not evolve with them; landowners need to have bottom rung unbarred

Habitat degradation

The process where a habitat is partially disrupted by human or natural activities, making it less suitable for its native species but not entirely destroying it

• Most widespread form of habitat destruction

Types of pollution

• Pesticides

• Oil spills

• Toxic metals

• Eutrophication

• Acid rain

• Pharmaceuticals and personal care products (PPCPs)

• Plastics

Biomagnification

The increasing concentration of toxic substances in organisms at successively higher levels in a food chain

Bioaccumulation

The process where a chemical’s concentration increases in an organism over time, as it is taken in faster than it can be broken down or excreted

Types of exposure from oil spills

Direct exposure

• physical contact with oil, such as touching it or breathing in fumes

Indirect exposure

• can affect people farther from the spill, typically through contaminated food or long-term environmental damage

Eutrophication

The process where a body of water becomes overly enriched with nutrients, particularly nitrogen and phosphorus, leading to excessive growth of algae and aquatic plants and the depletion of dissolved oxygen

Acid rain

Release of nitrogen and sulfur oxides into the air

• Creates nitric and sulfuric acids that lower pH in rainwater

• Weakens and kills trees

• Increased acidity in bodies of water

PPCP

Pharmaceuticals and personal care products

• Medicines used by people and livestock

• Personal health or cosmetics

• Discharged directly into surface waters or into plumbing and sewer systems

Plastics

• Entanglements

• Ingestion

• Don’t biodegrade

• Can photo-degrade into smaller particles (micro plastics <5mm)

Plastics examples

• Turtles ingest plastic bags they believe are jellyfish

• Albatros feed their young plastic

Disease effects

1. High rate of contact between host and pathogen encourages the spread of disease

2. Indirect effects of habitat destruction can increase an organism’s susceptibility to disease

3. Infectious disease can spread between wildlife populations, domestic animals, and humans as a result of increasing human densities

4. An animals usually removes itself when sick but with nowhere to go, they stay in contact with other individuals

How disease increase with habitat destruction

• Crowding and increased density leads to increased spread of disease

• Habitat fragmentation can cut off populations and decrease genetic diversity

• Decreased resources can make individuals more susceptible to disease

Wildlife and human disease dispersal

• Living close to wildlife can increase disease transmission

  • from humans and livestock to wildlife

  • from wildlife to humans

• Habitat destruction

• Exploitation of wild animals

• Smaller populations reduce animals resistance to disease

Zoonotic disease

Diseases that arise from animals and then can infect humans

Disease examples

North American bats

• Crowding

  • many bat species roost together in large colonies where disease can spread more easy

• Humans

  • humans spread white nose fungus when they travel from one cave to the next

Black footed ferret

• Habitat destruction

  • loss of their main prey (prairie dogs) led to population declines

  • sylvatic plague and canine distemper wiped out populations

Tasmanian devil

• Tasmanian devil facial tumor disease

• Social structure

  • biting is a way of playing, leading to spread of disease

Endemic Hawaiian Birds

• Habitat destruction

  • fewer spaces to occupy

• Endemic island habitat

• Invasive species

  • mosquitos (malaria)

Reasons for zoonotic disease spread

• Increased human densities increasing human-wildlife interactions

• Overexploitation of some species (bushmeat, wildlife trade, pet trade, etc) exposes humans to wildlife diseases and increases risk of transmission

Bushmeat

Raw or minimally processed meat from wild animals

• Particularly from Africa, Asia, and Latin America

Invasive species

Non-native organisms that cause harm to the environment, economy, and human health by disrupting ecosystems and outcompeting native species

• No natural predators

• Wort invaders: Rats, domestic cats, domestic dogs, wild boars, domestic goats, and domestic cows are all invasive and heavily impact birds

  • Batrachochytrium dendrobatidis (fungus) heavily impacts amphibians

How species invade

1. European colonization

2. Agriculture, horticulture, aquaculture

3. Accidental transport

4. Biological control