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what is habitat?
the range of environmental conditions (biotic and abiotic) that a species needs
unique to each species
not a geographic location
inhospitable matrix
where the fragments live
area that is not suitable for a specific species
habitat loss comes in many forms
clear cutting
agriculture
housing
roads
fragmentation has
has genetic impacts (inbreeding and the ability to adapt)
ecological impacts (a reordering of the whole community)
can alter processes (how nutrients flow through the system)
how does habitat loss and/or fragmentation lead to changes in genetic diversity and why does it matter?
genetic diversity is good for individuals
genetic diversity is required for adaptive evolution—-especially important in an era of rapid climate change
traits of a population that maintains genetic diversity
large population size
mutations occur
drift is minimized
even sex ratios
random mating
avoids inbreeding, inbreeding depression (ID)
migration between populations
three factors that drive population decline
environmental stochasticity
demographic stochasticity
genetic stochasticity
stochasticity = variation that can’t be predicted
extinction vortex
population numbers dip —> small, slow increase —> population numbers dip again and tend to stay that way for longer
species-area relationship (SAR)
S = C x Az
S = number of species
C = constant, equal to the number of species in the smallest sampling unit (y-intercept)
A = area
Z = rate at which new species accumulate (slope)
log(S) = log(C) + zlog(A)
why are some species much more sensitive to fragmentation than others
depends on their size, mobility, how skittish they are, their boldness and shyness
oceanic islands
not nested because of randomness and competitiveness and vulnerability to extinction, colonization and survival
never attached to mainland
only species there are those that made their way across an ocean by themselves
species with great dispersal abilities
islands are species-poor: few mammals and few top predators (mesopredators become apex predators)
land bridge island
once attached to mainland, become separated slowly
contain more species per unit area than oceanic island of same size
have species that could never have made it to the island on their own
nested
habitat islands
created by habitat destruction
exist in a matrix of inhospitable habitat
non-nested because of random extinction
more similar to oceanic islands
faunal relaxation
it takes a while for species to be lost once a land bridge or habitat fragmentation forms…what you see immediately is not good indication of the long-term outcome
extinction debt
species ‘committed to extinction’ owing to habitat loss and reduced population size but not yet extinct
richness
total number of species
not all species are equally vulnerable to extinction following habitat loss
we lose a specific subset of species first
species that require large areas
those species also tend to have large, community-wide effects (apex predators and mega-herbivores)
trophic cascade
indirect effect of one species on another that is at least one trophic level removed
example: predators are eating herbivores which minimizes the animals eating the plants—the plant’s predators
SLOSS
a single large reserve or a several small reserves
which is better depends on species area curve
several small advantages
are less nested
they are better protected from external factors (ex: wildfires and diseases)
higher density
single large advantages
more species (large) to protect
may better protect species with large home ranges
less edge effect
more connectivity
larger population less prone to extinction/decline
edge effect
the changes in population or community structure that occur at the boundary between two different habitats
native species
a species that occurs where it evolved in situ
still a native species even if it once required colonizing a distant location—as long as they did it without the help of people
exotic species
a species that has been moved by people—intentionally or unintentionally—to a region where it did not evolve
invasive species
a subset of exotic species that have large ecological or economic impacts
invasions
the human-mediated redistribution of species to areas where they do not naturally occur/did not evolve/they did not colonize without human assistance
exotic species vs. invasive species
exotic species: have little/no ecological impact
invasive species:
spread on their own into wildlands
establish large, self-sustaining populations
directly displace native species (competition or predation) or indirectly by altering ecological interactions (disrupt mutualisms)
and/or alter ecosystem processes
invaders can be ant taxa
plants
diseases
invertebrates
vertebrates: mammals, fish, reptiles
biological invasions
intense competition with native places
alteration of the aquatic environment so that it is unsuitable for native species
impacts pollinators—parasitoids and herbivores
disrupts a highly coevolved mutualism between a plant and its pollinator/seed disperser
what is the biggest way for invaders to cause ecological impacts
by altering disturbance regimes
disturbance regime
any natural, external event that removes established plants very quickly
examples: fire and floods
why are invasions different than naturally-occurring colonization events?
rate of colonization, abundance upon arrival
identity/trophic role of the colonist
consequences of invasions
homogenizing flora and fauna globally
loss of endemic species
created exotic communities
disruption of native ecosystem processes
lowering diversity—less diverse communities are less stable
three requirements for every invasion
propagule supply: has to be a sort of invasive species introduced
characteristics of the invader: needs to be well-suited to the local conditions
community invasibility: susceptible to invasion
diversity-invasibility relationship
more diverse communities should be less susceptible to invasions compared to less diverse communities
how can diversity promote invasions
native species can also assist invasive species
the more diverse the community is, the more likely it is to contain a species that can act mutualistically with the invader
biotic resistance
the ability of communities to resist exotic invasions
disturbance
removal of established plant biomass
examples: fire, flood, hurricanes, drought, volcanic eruptions
resilience
how quickly did they recover
resistance to disturbance
plant community is altered very little by levels of disturbance
resilience following disturbance
the community return to its pre-disturbance composition quickly following disturbance
diseases
primary cause of large mammal die-offs
affect community structure much like apex predators and trophic cascade
when do you expect strong effects of diseases
social, congregating animals
dense populations
examples: dominant plants, coral
allow infected individuals to come into contact with susceptible ones
extirpations
the extinction of a population of a species
novel disease
virus that hasn't been found in humans in the past
novel diseases and more severe outbreaks of native diseases
greatly reduce the sizes of their host populations
have cascading effects on other species in the community even when the disease attacks a single host species
major driver in infectious diseases in humans
habitat fragmentation/encroachment and bushmeat trade
examples: COVID-19 and HIV
some clear patterns are emerging
increasing the number of pathogen generations per season
expanding the geographic range of the disease
increasing or decreasing transmission rates (depending on changes in host density)—direct effect of climate change
changing susceptibility of host
exposing some hosts to novel pathogens
example: COVID-19
healthy carriers
have the disease without any of the symptoms
what does cloud cover do to nighttime temps? daytime temps?
cloudy days = days get cooler
cloudy nights make nights warmer…the earth is radiating heat out and the clouds act as a blanket keeping it in