bio iq final prep - (habitat loss to infectious disease)

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?

1. genetic diversity is good for individuals

2. genetic diversity is required for adaptive evolution—-especially important in an era of rapid climate change

traits of a population that maintains genetic diversity

1. large population size

   • mutations occur

   • drift is minimized

2. even sex ratios

3. random mating

   • avoids inbreeding, inbreeding depression (ID)

4. migration between populations

three factors that drive population decline

1. environmental stochasticity

2. demographic stochasticity

3. 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 A^z

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

1. species that require large areas

2. 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 any 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?

1. rate of colonization, abundance upon arrival

2. 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

1. propagule supply: has to be a sort of invasive species introduced

2. characteristics of the invader: needs to be well-suited to the local conditions

3. 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