Lecture 7 - Connectivity and Fragmentation

metapopulation

group of populations that occupy habitat patches and where individuals can move between patches at least a little bit

dispersal

movement between patches

if there’s dispersal, we say the patches have…

connectivity

connectivity ranges from low (little dispersal) to high (lots of dispersal)

fragmentation

human impacts are changing connectivity for many species

cities, roads, agricultural land and other land-use changes fragment habitats - diving them itno smaller patches

what happens when a species’ range is fragmented?

there’s less connectivity across metapopulations

are highways the only roads that impact biodiversity?

no - all kinds of infrastructure and resource extraction requires access roads - wind turbine farms, solar farms, natural gas fields, logging sites, etc.

these roads can have a devastating environmental impact regardless of if they’re for renewable energy or not

roads are a kind of distrubance that permanently fragment a landscape and invasive plant species often appear as the early succession species after that disturbance

fragmentation and extinction risk

fragmentation splits ranges into patches

we kniw that smaller ranges = higher extinction rate

if a species’ range is really fragmented, there’s a chance each population individually will go extinct until last surviving population is gone

reduced connectivity means reduced gene flow - when a population is small and unconnected to otheres, there’s a risk of inbreeding depression

inbreeding

when closely related individuals reproduce - if a populatoin is small, indidivuals may become closely related eventually

why is genetic diversity important?

means there will always be a few healthy individuals that are well-adapted to a variety of environmental conditions

inbreeding depression

whta happens when there’s no genetic diversity, leading to a loss in fitness because

(1) rare disease causing genes can become widespread and

(2) gene combinations that confer greater health can be lost

**also without genetic diversity, there’s less individual variety so when habitat and climate conditions change, perhaps none of the individuals will be well-adapted to the new conditions

cheetahs and inbreeding depression

inbreeding depression is a constant conservation concern for cheetahs

cheetahs have less genetic diversity than any other type of cat

cheetahs in captivity had the highest death rate to feline coronavirus ever recorded likely since the virus evolved to escape one cheetah’s immunity and escaped all of their defense systems

ways to restore connectivity

• overpasses

• underpasses

• tunnels

overpasses

tall fencing runs on either side of the highway, before and after the bridge

when wildlife walk up to the fence, they run into it and then follow it parallel to the highway until they get to the bridge, then cross the bridge and can safely cross

**sometimes fence or earthen berm are engineered to quiet the road noise for animals looking to cross

overpasses work but only when built to specificaiton

scientists have collected data that says they need to be at least 50m for many different species to use them but most transportation agencies build smaller ones to save money bc it odoes cost about 5-15M

built properly, wildlife overpasses reduce collisions with wildlife by more than 80%, and up to 96% for deer and elk

reducing collisions with big animals also saves human lives

underpasses

some big species like elk prefer overpasses but other species like cougars prefer underpasses

tunnels

amphibians need a dark, moist route to travel and would get dried out or eaten on a regular wildlife overpass so they need a tunnel system

**tunnels really help amphibians and reptiles

salamander tunnels

spotted salamanders make annual migrations to vernal pools to breed which means crossing roads = high fatalities

there are two tunnels in amherst massachusetts but most of their crossings are unprotected

people who love salamanders go on rainy nights and help as many cross as they can

wallis annenberg wildlife crossing on 101 freeway

under construction, planned to be biggest wildlife corridor in the world

in 2015 - NWF and caltrans proposed massive corridor across 101 in agoura hills at liberty canyon

wallis annenberg fonudation and 3000 other orgs donated $34M, reaching funding goal in 2022 (california paying other $58M)

many collaborating agencies helping

research began in 1990 to link santa monica mountains and simi hills to prevent local cougar pops from going extinct but so much of the land was privately owned —> SMMC, MRCA, and NPS spent 30 yrs acquiring enough land to make it possible

santa monica mountains conservancy

state agency established by california legislature in 1980 to protect and restore southern california lands for benefit of both wildlife and californians

mountains recreation and conservation authority

local public parks agency that manages the SMMC lands and its own lands

wallis annenberg wildlife crossing current status

as of march 2025: began putting soil down on top of the overpass as the basis to plant coastal sage scrub speciesnative to santa monica mountains

additional 12 acres are being restored w/ 50,000 native plants

wildlife corridors

areas that reconnect populations in a fragmented landscape - main routes animals take getting from one patch to another

effective land-use planning studies wildlife movement to find where corridors are and avoid cutting them off w/ new roads or development

animals move according to topography and resource distribution of a landscape

wildlife crossings can become corridors but putting in a bridge doesn’t guarantee animals will use it - we have to do research, assessment, and monitoring

wind turbines and wildlife corridors

topography of long ridgelins makes them good for wind farms and wildlife corridors

many birds and bats die from collisions with turbines and more often when in a corridor

renewable energy isn’t without cost to the environment, just like electric batteries aren’t