Lecture 25 Human Impacts on Organisms Flashcards
Human impacts on the environment
- Humans have been transforming environments for millennia
- Recent decades have experienced drastic acceleration of modification
- All biomes have experienced 20-50% conversion to human use
slide 3
Threats to Biodiversity
Local and global scale processes lead to biodiversity loss
slide 4-6
Land Use Change: Habitat Loss
- Widely considered most important threat to biodiversity: If species have
nowhere to go, then do the other threats matter? - Contributes to 73% of species
that have become extinct,
endangered, vulnerable,
or rare - Agriculture is biggest
contributor, but also:
mining, logging, trawling,
urbanization - Most severely impacts:
large-bodied, wide-ranging,
specialist, migratory species;
endemics
slide 7
Habitat Loss: Freshwater Aquatic
- Dams, reservoirs,
channel modification,
flow regulation affect
most of world’s rivers - Wetlands filled in for
agriculture and
development
slide 8
Habitat Loss & Fragmentation: Deforestation
- 130,000 km2 of tropical forest are cleared each year
- Global forest area has been cut in 1/2 over last 300 years
- 50+ nations have lost 90-100% of their forest cover
Deforestation alters
hydrology, nutrients
in soil, and
microclimate
slide 10-13 and 15
Habitat Loss: Coral Reefs
- 70% of coral reefs have been damaged by human activities
- At current rate, 40-50% of reefs could disappear in next 30-40 years
slide 9
Deforestation: Madagascar
- More than 90% of
rainforest habitat has
been cleared - 90% of species are
endemic - Largest percentage of
species threatened or
endangered in the world - Humans are responsible
for extinction of 17
species and 8 genera
slide 14
Habitat Fragmentation
- Habitat is destroyed leaving
smaller unconnected areas - Smaller habitat fragments have
higher extinction probability - Creates “edge habitat” that favors
certain kinds of species (“edgeadapted”) - As patch size decreases, species
that specialize in forest interior
decline
Patches may function like a metapopulation, but dispersal can be dangerous!
Long-term ecological
research studies have
helped us understand
how populations are
responding to habitat
loss and fragmentation
slide 16-22
Habitat Loss & Degradation: Agriculture
11% of the Earth’s land surface is used
for crop production, 26% for livestock
- More than 80% of North American grasslands
have been converted to agriculture & other uses - More than just habitat loss!
- Crop harvesting removes nutrients from soil à
reduction in future plant productivity - Nutrient addition (next week)
- Fire often used to clear land à CO2 release
slide 23-25
Habitat Loss & Degradation: Urbanization
- More than ½ of humans
live in cities - By 2030, 5 billion people
expected to live in cities - Leads to loss of species
across all taxa and trophic
levels
slide 26-29
Habitat Loss & Degradation: Urbanization
- Many species are tolerant of urbanization… but most are not
- Many urban-tolerant species are non-native
- Urbanization leads to global biotic homogenization of ecological communities
slide 30
Habitat Degradation: Urban Heat Island Effect
slide 31
Overharvesting
- Overharvesting
(overexploitation): of wild
organisms at rates exceeding
the ability of their
populations to persist - Not just food – many species
poached because of economic
value - Most severely impacts:
- Species with restricted
habitats - Large organisms with low
reproductive rates
Overharvesting: Hunted to Extinction
slide 33-37
Overharvesting: Hunted almost to Extinction
- Northern elephant seals - only 20 individuals in 1890s
- Rebounded to >150,000 today (but very low genetic variation)
slide 38-39
Overharvesting: Fishery Collapse
- Fish populations once thought to be inexhaustible now decimated
- Particularly effective and damaging harvesting technologies: long-line, trawlers
- Industrial-scale fishing operations
Fishing down the food web:
As fish stocks of top trophic
levels (predatory fish)
decline fisheries are looking
to lower trophic levels
slide 40-43
Overharvesting: Poaching
- African elephants declining in most
of Africa for last 50 years, largely
because of ivory - International ban on sale of ivory
led to increased poaching (illegal
hunting) - 2006-2015: elephants dropped
from 525,000 to 415,000 (22%
decline) - If this continues – elephants could
become extinct in wild!
Invasive Species
- Introduced species are
moved (intentionally or
accidentally) from native
range to a new region by
humans - Species introductions are
nothing new… but global
connectivity of the world
today makes them more
common - Introduced species become invasive species when they have a negative
ecological impact on native species & often cause economic harm - Outcompete native species for resources or habitat
- Consume native species
- Introduce pathogens to naïve populations
- Contributed to
40% of extinctions
since 1750 - Cost billions in
damage and
control - > 50,000
introduced
species in USA!
slide 45-47
Unintentional Introductions: Brown Tree Snake
- Introduced to
Guam after WWII
in military cargo - 12 species of
birds, 6 species
of lizards have
gone extinct
Unintentional Introductions: Chestnut Blight
- American Chestnut was dominant tree in eastern
North American deciduous forests prior to 1910
(>40% of trees were chestnut) - Fungus imported with Asian Chestnut tree
- American chestnuts no longer exist as mature
trees but only as stumps barely hanging onto
existence and unable to reproduce
Intentional Introductions: Kudzu
Introduced to control erosion and as an ornamental plant
slide 50
Human-Wildlife Interactions
Habitat loss, transformation, and environmental change force species into new regions
where they may have closer contact with humans leading to conflict and disease
slide 51
Human-Wildlife: Conflict
Threats to crops, property, livestock, and human safety lead to increased
persecution of species & contribute to decline
Human-Wildlife: Disease
- Organisms become more
susceptible to disease in
degraded ecosystems - Humans unintentionally
spread disease to wildlife
and vice versa - Habitat loss and
fragmentation alters
abundance and dispersal
of pathogens and their
animal hosts and vectors
slide 53
Human-Wildlife: Zoonotic Disease
- ¾ of emerging human diseases
are zoonotic diseases
transmitted to humans from
other animals - May be transmitted by direct or
indirect contact, or via a vector
(intermediate species, often
parasites) - Examples: Rabies, plague,
Chagas’, salmonella, sleeping
sickness, Malaria, Lyme, Nipah,
ebola, zika, monkeypox, avian flu,
intestinal worms…
Zoonotic Disease: Lyme
- Caused by bacterial parasite Borrelia burgdorferi
- Transmitted by blacklegged tick (Ixodes scapularis)
- Forest loss and fragmentation leads to higher densities
of infected ticks - Found in NYC!!!
6th Mass Extinction?
- Extinction is a natural
phenomenon occurring since life
first evolved - Extinction rate now is alarmingly
high compared to past - More than 1,000 species extinct
in past 400 years: 100 to 1,000
times background rate - We will lose many species before
we even know they exist!
slide 56-58
Extinction Vortex
- Small populations are
particularly vulnerable to
threats - Extinction vortex: downward
population spiral of small
populations because of the
combined effects of
inbreeding and genetic drift - Effects of inbreeding and
drift become more harmful
as the population shrinks!
slide 59
Extinction Vortex: Prairie Chicken
- Greater Prairie Chicken
used to be common in
Eastern US - Numbered in the
millions in 1800’s - Introducing new
genetic variation
rescued population
from downward spiral
slide 60
Extinction Vortex: MVP
- Minimum Viable Population (MVP): the size a population must be to assure
long-term survival - Vertebrate estimates ~1000 per population, invertebrates ~10,000
- Depends on life history and dispersal ability
- If below MVP, extinction vortex or catastrophes can eliminate the population
slide 61
Extinction Vortex: Effective Population Size
- How do we know if a population
is too small (below MVP)??? - Not all individuals in a
population breed successfully - Actual genetic variation of a
population is a subset of the
total population - Effective population size (Ne)
estimates the size of a
population based on only
successfully breeding individuals
Extinction Vortex: Effective Population Size
- Effective population size more
accurately reflects the genetic
diversity (and adaptive potential)
of a population - Ne can be used to conduct a
population viability analysis to
quantify the risk of extinction - MVP can be used to know how
much habitat must be preserved - Larger parks needed for larger
animals!
slide 63-66
Extinction Debt?
Extinction Debt: the future extinction of
species due to events in the past, owing
to a time lag between an effect and the
subsequent disappearance of species
By some estimates more than 80% of
expected species losses are yet to come!
slide 67
