Author: Bruce E. Fleury
Last saved by: Fleury
Company: Tulane University

Conservation II

•	Look at this typical view of rural America, a random slice of the northeastern US
•	Notice how few patches of unbroken forest remain, and how isolated they are from one another

•	Loss of habitat, and fragmentation of the remaining habitat, are the single greatest threat facing all species today
•	Unless we can stem the tide of global habitat destruction, we may be facing one of the greatest mass extinction events in the history of our planet

•	Why do species go extinct in fragments?
•	What can we do to minimize the damage caused by loss of habitat and fragmentation of habitat?

•	Ecological mechanisms behind increased extinction rates in fragmented habitats:
>	Many species have a minimum home range or territory size
>	Niches are lost when diverse habitats (heterogenous) become lost or simplified (homogenous)

•	Ecological mechanisms behind increased extinction rates in fragmented habitats:
>	Biotic interactions are disrupted (predator/prey, plant/pollinator ex.)
>	Edge effects - algebraic consequence of decreasing area

•	Many species have a minimum home range or territory size
•	If the fragment is smaller than their minimum requirements, they will soon go extinct in that fragment
•	Especially true for large vertebrates - bears, cougars, eagles…

•	Niches are lost when diverse habitats (heterogenous) become lost or simplified (homogenous)
•	Smaller habitats tend to be less diverse than larger ones, encompass fewer habitat types, hence fewer niches

•	Larger areas are more likely (by pure chance) to contain more species and more individuals (sample effect)
•	Especially true if your species has a patchy distribution - few here, few there - large area will likely contain more of them…

•	Both of these problems - minimum range/territory, habitat diversity - can be addressed by considering the theory of island biogeography
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Remember the theory of island biogeography?

•	Theory of island biogeography - the equilibrium number of species on an island will be a balance between the opposing forces of immigration and extinction
•	Shrinking fragments of habitat can be viewed as islands in a hostile sea…

•	Theory of island biogeography predicts that larger islands should support a greater number of species
•	One large wildlife refuge should be better than several small ones  

•	Smaller refuges tend to be less diverse - fewer habitat types, more homogenous
•	Might be too small for many species who need more space to hunt, breed…
•	Area-sensitive species need minimum amount of space to survive or reproduce

•	Supported by several studies on the relationship between species diversity and land area
•	West Indies survey, ex. - number of amphibian and reptile species correlates strongly with island size

•	Biotic interactions are disrupted in fragmented habitats 
>	Predator/prey, plant/pollinator, symbiotic partners
>	Decreased availability of mates
>	Increased competition, parasitism, predation

•	Biotic interaction are disrupted between predator/prey, plant/pollinator, symbiotic partners…leads to secondary extinctions
•	As the fragment shrinks, the likelihood increases that one partner will be left out or go extinct, takes with it all organisms that depend on it for survival

•	Decreased availability of mates in small fragments
•	Ovenbirds ex. (Gibbs and Faaborg 1990)
>	Only 25% of males found mates in small forest fragments (<140 ha)
>	75% of males found mates in larger fragments (>500 ha)

•	Increased competition, parasitism, predation in fragmented habitats
•	Competition increases as surviving individuals cope with reduced area
•	Edge effects - algebraic consequence of decreasing area - helps explain why this happens

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Consider a large circular habitat…
•	Circumference (edge) of a circle?
>	2 π r
•	Area of a circle?
•	π r^2

•	Because r^2 increases much faster than r:
>	Larger circles have more interior space relative to their edge
>	Smaller circles have more edge relative to their interior
>	As habitat fragments shrink, they develop relatively more edge, and less interior space

•	This simple fact has many consequences for preserving biodiversity, managing parks…
>	Increased edge shifts the balance of diversity towards species who do well in edge habitats
>	Increased edge in smaller fragments means increased competition, increased parasitism, increased predation

•	Edges often highly diverse, mixture of edge and interior species
•	Blue jays, deer, many predators prefer to feed along edges of fields, forests…
•	Increased edge shifts the balance of diversity towards species who do well in edge habitats

•	Competition increases along edge and in the interior as fragment continues to shrink
>	Species that normally forage in the interior ex. may be forced to forage along the edge, competing with species that normally forage along the edge
>	Edge species may push farther into the interior as competition increases and interior shrinks

•	Many species need deep interior space to breed, can’t thrive in fragments
•	Especially true of tropical species, who are very prone to extinction from edge effects

•	Songbirds are vulnerable to edge effects - lower nesting success near forest edges
•	Cowbird parasitism ex., is much greater in fragmented habitats
•	Cowbirds are brood parasites - don’t build nests, put their energy into laying their eggs in nests of other birds, let them raise young

•	Host birds end up raising large baby as if it were their own, may die of exhaustion 
•	Infants die from inability to compete with much larger cowbird for food
•	Brood parasitism is significantly higher in small forest patches (Temple and Carey 1988)
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Cowbird population recently exploded
•	Pre-colonial population restricted to more open western habitats
•	Vast eastern forest cleared, cowbirds expanded their range to the east

•	Rise of rice agriculture in the south fueled their rapid population growth
•	Disastrous results for many species of songbirds
•	Louisiana has three species - brown-headed cowbird, bronzed cowbird, shiny cowbird

•	Long-term study in the Amazon forest of ecosystem size and biodiversity - Minimum Critical Size of Ecosystems Project
•	Running over 30 years, managed by the World Wildlife Fund and the Brazilian National Institute for Amazon Research

•	Project has charted the many types of change that take place in edge habitats
>	Abiotic - increased light, wind speed, increased temperature, decreased humidity
>	Biotic - Changes in vegetation type, overcrowding of survivors, shift in balance of edge (light-loving) vs. interior species

•	What does all this suggest as the best strategy for managing our precious and shrinking fragments of habitat?
•	Combine island biogeography with common sense, basic algebra of edge/interior space…

•	As habitats become fragmented, fragments continue to shrink, fragments become more and more like islands in the storm
•	Between islands lies a hostile sea, little food or water, little or no cover, areas patrolled by urban predators - cats, dogs, people

•	What does the algebra of edge vs. interior suggest as a management strategy to preserve biodiversity in fragmented habitats?

•	We should try to minimize the amount of edge in a park or preserve
•	Circular tracts with smooth edges are ideal
•	Long narrow rectangles also suffer from edge effects - should avoid them
•	Avoid introducing interior edge

•	Interior edge is a major problem
>	Any space cleared in the interior - roads, parking lots, buildings - introduces edge habitat into otherwise unbroken interior
>	Circle with jagged edges would also have more edge vs. interior
•	Ideal refuge would be circular, unbroken…
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Construction of highways into remaining unbroken habitats and large fragments leads to their demise
•	Bubba effect - part of the edge effect is due to Bubba

•	Roads benefit only a few - loggers initially, followed by hunters, tourists, developers
•	Highways are often federally funded - Clinton’s big legacy is pulling the plug on financing new roads or repairing existing timber roads in federal forests

•	What does the theory of island biogeography suggest as a management strategy to preserve biodiversity in fragmented habitats?

•	How do species move from fragment to fragment (island to island)?
•	If a species goes extinct in a fragment, it can only be replaced by immigration from another fragment or “mainland”
•	What affects the rate of immigration to this island habitat?

•	Rate of immigration depends on
>	Distance from the island to the mainland (near or far?)
>	Dispersal ability of the colonizers 
–	birds good, snails bad…
–	waif dispersal (squirrel on a log)

•	Species will not recolonize fragment if there is no longer any way to get there
>	Need some way to reach the next island
>	Shrinking of fragments is equivalent to moving islands farther away from one another

•	If we wish to avoid local extinctions, we must provide a way for species to immigrate from one fragment to the next, or from mainland to fragment “island”
•	One solution is to design corridors between fragments of habitat

•	Corridors are natural areas that can be safely used by plants or animals to move from one habitat fragment to another

•	Lovejoy et al (1986) - Amazon forest fragments quickly lost species, but corridors could preserve biodiversity in small interconnected fragments
>	Corridors needed to be 100-300 meters wide
>	Needed at least one “mainland” in the network, area of at least 1,000 hectares

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Most species exist as scattered groups of local population
•	Local populations interbreed with one another
•	Metapopulation - new view - sees populations as a matrix of scattered but interacting local populations

•	Local populations may go locally extinct in scattered patches of habitat, often recolonized later on from another fragment
•	Look at the “big picture” of metapopulations, populations in fragmented habitat show “winking patches” (Villard 1991)

•	Species flicker on and off in different patches due to immigrations and extinctions
•	Overall population size can remain stable despite local losses
•	As long as immigration is possible, local extinctions will be only temporary

•	Beier (1993) modeled effects of corridors on the survival of mountain lions in California

•	In the absence of corridors, a population of 15-20 lions can be preserved in an area of 2200 km^2
•	With corridors that allow the immigration of one new female and three new males every ten years, could maintain 15-20 lions in only 600-1600 km^2

•	Rescue effect - small populations can be maintained in smaller areas, as long as the population can be rescued by immigration from other patches

•	Most ambitious corridor proposed to date is the Y2Y corridor - the Yellowstone to Yukon Conservation Initiative
•	Aims to connect Yukon wilderness with smaller wilderness areas in the southern Rocky Mts.

•	Corridor would connect Yellowstone, Glacier National Park, several parks in Canada
•	Could ensure the survival of the Grizzly bear, now relatively isolated population in Yellowstone and nearby areas

•	Corridors would restore connectivity - landscape was more interconnected before we disrupted it for development
•	Immigration between habitats was much easier in pre-colonial days

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Some problems with corridors
>	Don’t know if all species would use them
>	Don’t know minimum width for species to use
>	Passage is perilous, exposed to hunters, predators etc. in corridors
>	Could spread fires, diseases etc…

•	Population size is also a critical concern - need to preserve genetic diversity 
•	Need to preserve genetically viable populations
>	Avoid too much inbreeding
>	Genetic drift, genetic bottleneck are critical problems for species w/ small surviving popns.

•	What is the minimum viable population size (MVP) ? 
•	MVP - minimum population size needed to maintain genetic viability of a population 

•	Ecologists disagree on how many individuals need to be preserved to preserve genetic diversity, keep species healthy
•	Polarities of this argument summed up in the 50-500 Rule
•	Need minimum of 50 individuals or min. of 500 to preserve genetic viability??

•	Animal breeders, farmers “rule of thumb”, need about 50 for a healthy herd
•	Population genetics models predict closer to 500 is the necessary minimum

•	Truth is, we just don’t know….
•	Populations may need to be much larger than that to survive random events, disturbances - forest fires, diseases…

•	Jones and Diamond (1976) - bird populations in California’s Channel Islands
•	Smaller populations disappeared more frequently than larger populations (duh…)
>	Fewer than 10 pr., < 39% in 80 years
>	10-100 pr., <10% in 80 years
>	If >1,000 pr., stable over 80 years

•	Even though we don’t know MVP for most species, it makes sense to maximize genetic variation wherever possible
•	Modern zoos use ISIS to ensure maximum outbreeding of captive species

•	ISIS = International Species Information System - online database (studbook)

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Zoos use ISIS to decide which animals to exchange for mating, maximize outcrossing, minimize inbreeding
•	Audubon Zoo is among the world leaders in the preservation of endangered species
•	ACRES - Audubon Center for Research on Endangered Species (West Bank)

•	Frozen zoo - Dr. Betsy Dresser’s cryogenic storage of frozen viable embryos - use hosts to develop when frozen
•	Used domestic cat as a surrogate mother to give birth 11/99 to an African wild cat named Jazz, born from a frozen embryo

•	Dresser later trumped her own ace by cloning Jazz
•	Clone kitty Ditteaux was born in August 2003
•	First clone of a wild carnivore

•	Zoo announced in 2014 a new collaboration with the San Diego Zoo “Alliance for Sustainable Wildlife”
•	1,000 acre site will be devoted to captive breeding of large flocks or herds of about 2 dozen threatened or endangered species

•	Several strategies to preserve biodiversity:
>	Refuge size - larger is better
>	Refuge shape - smooth circular best
>	Avoid interior edge

•	Several strategies to preserve biodiversity:
>	Establish corridors to encourage immigration
>	Target partners in biotic interactions
>	Maintain minimum viable population size
>	Preserve genetic diversity in zoos etc…

•	What if we are successful in preserving endangered species in zoos?
•	Preservation is pointless unless we can eventually restore habitats, reintroduce species

•	Restoration ecology is a booming field
•	Even a strip mine can be restored to functional habitat
•	Mitigation of wetlands and other habitat types is increasingly required by law - ACRES is built near a mitigated wetland

•	Reintroductions can be very problematic
•	Consider the case of the gray wolf…
•	Reintroduction of the gray wolf into the Adirondack Park raised howls of protest…

•	Adirondack Park (my boyhood back yard!) is the largest park in the lower 48 states (!)
•	Total area = 24,000 km^2
•	Numerous communities in or near its boundaries, a few (very) small cities like Lake Placid - tourist mecca…
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130,000 people live in or near the park
•	60% of the park is still private land, operated under close state supervision
•	Wolves ordinarily prey on elk, deer, moose, beaver…natural prey

•	Residents fear that hungry wolves will turn to pets, livestock, children…
•	Complicating matters, coyotes have invaded the park, filled the wolf’s niche
•	Wolves and coyotes would be competing for limited deer and other prey

•	Latest and greatest proposal for restoring native habitat is the “Buffalo Commons”
•	Proposed in 1987, Drs. Frank and Deborah Popper
•	Would turn most of the Great Plains into the worlds largest nature preserve

•	Like the Adirondack Park, would include many cities, towns etc.
•	Try to bring back the prairie grasses and the great buffalo herds, elk, wolves, etc…
•	Switch from farming economy to ecotourism on a grand scale

•	There is no easy solution…
•	It is up to us to find a way to accommodate our civilization to wildlife
•	If we do not, despite our teeming human population, our children will inherit a very lonely planet….