April 20, 2012
One characteristic shared by the two islands is how susceptible their ecosystems are to disturbance, as exhibited by the crashes of their island fox population. Although different in cause, each demonstrated that a small island ecosystem, evolving under sheltered protection from mainland disturbances can create unique and fragile ecosystems that do not handle major disturbances well. This is largely due to their relatively small gene pool of the population and small geographic range.
In other more traditional geographic regions, a disturbance in an ecosystem that leads to a population crash can often be followed by an easier recovery. Either there is a large enough, well-adapted surviving population that can repopulate, or organisms from another region can gradually be reintroduced into the area. However on an island, often neither is possible. If the species experiencing the crash is endemic, then it is possible that the crash will result in the species extinction as no other existing members of the species exist in the world. Even if some individuals survive the initial disturbance, with the population, small to begin with, may leave so few survivors that the gene pool does not carry enough diversity for a proper recovery and the species may die out. As such, a disturbance in an island ecosystem is much more likely to lead to species extinction.
On Catalina Island, the collapse of the fox population was primarily due to the introduction of the canine distemper virus. In 1999 an outbreak occurred causing the population to drop from 1300 to only 100 animals. The outbreak swept across the west side of the island but fortunately did not reach the eastern island, which was separated by a narrow isthmus. In 2000 the Catalina Island Conservancy and the Institute for Wildlife Studies instituted the Catalina Island Fox Recovery Plan, which consisted of monitoring, captive breeding, vaccination, and relocation of the foxes. The program was a success and by 2004, the population had climbed up to 300. Although it is not entirely known how the virus was introduced into the population, one theory is that it was brought to the island by an infected domesticated dog or a stow-away raccoon.
On Santa Cruz Island, a collapse also occurred, but for different reasons. Over-predation by the golden eagle, an exotic species, was discovered to be the primary cause. However indirect blame could be placed on the human introduction of pigs to the island. A study by Roemer et. al. indicated that the colonization of Golden Eagles onto the island could only be sustained by the existence of a feral pig population. However, even though the foxes alone could not sustain the eagle population, they were much more affected by eagle predation than the pigs. The foxes were ill adapted to evade eagle predation and as such faced possible extinction.
Like the island fox’s unfortunate fate at the hands or claws of introduced species and viruses, many native and endemic plant species on both Catalina and Santa Cruz islands have suffered from human introduced grazers. While both islands have gone under some form of plant restoration from the damages done by past-introduced grazers, Catalina currently still has resident populations of non-native grazers while Santa Cruz Island does not. This provides an interesting contrast between the islands because there are many similar native plant species that exists on both islands but in different quantities and manifestations. Through this comparison one can clearly see the tremendous impact that grazers have on the plant communities of the Channel Islands.
Catalina currently has a small population of 150-200 bison that roam the island. The bison population is controlled both by a birth control that limits the number of calves a female bison can have a year and by shipping the bison back to the mainland to supplement mainland herds on tribal lands. The birth control method was introduced in 2009 and was greeted by animal rights activists who opposed the Catalina Conservancy’s earlier eradiation of feral goats and pigs with high power rifles from helicopters. The Los Angeles Times reported that the birth control option for controlling the bison herds was suggested by an animal activist Avalon shop owner named, Debbie Avellana. Other non-native grazers that continue to roam the island are mule deer that are kept under control by recreational hunting as well as the Conservancy, and a very small population of black buck antelope. Historically Catalina was used for grazing goats, pigs, sheep and cattle but have since been irradiated.
Catalina’s current native plant population has suffered as a result of the current non-native grazers on the island. The effect of the grazers can be seen all too clearly in the example of the native Giant Coreopsis (Coreopsis gigantea). On Catalina this “Dr Seuss plant” is only found with in the confines of the Ackerman Nursery where grazers are kept out. There are also reports of some wild species on the sea bluffs or steep gullies of the island where grazers can’t get to them. On a whole plants on Catalina tend to be bush-like where they otherwise would be more like trees. The only “trees” you will find on Catalina are either non-native or are the native toyon, lemonade berry, sugar bush or Catalina Cherry trees because they are so resilient. Some native plants have changed their pollination season to try and outcompete not only the grazers but also invasive plants.
Restoration on Catalina is difficult because there is a permanent human population there and the island attracts around a million tourists a year. This constant stream of visitors means the potential for foreign species introduction is more likely. Fennel is still a problem on the island being an aggressive invasive species, but a management strategy including weeding around campsites and populated areas outward seems to be working in its early stages. Another invasive species is the eucalyptus, which was brought to the island on purpose to beautify areas like Avalon and was a favorite of the Wrigleys. Santa Cruz Island also struggles with both eucalyptus and fennel.
Santa Cruz Island does not have any non-native grazers currently living on the island. Historically Santa Cruz Island was a ranch raising some of the most well known beef and sheep products on the west coast. Since then it has been brought under the control of National Park Services and the Nature Conservancy. The only human presence is that of campers and eco-tourists, and researchers. There are a few people that live there to maintain the research and historic ranch facilities. These conditions have allowed a recovery of many native plants and allows for these plants to grow large and where on Catalina you may have a sparse bush, on Santa Cruz Island you will have a large bush as tall as a man. On Santa Cruz Island, Giant Coreopsis and Bedstraw are significantly more common than on Catalina as are buckwheats (including one species of buckwheat that is endemic to Santa Cruz Island), Manzanita (also including a endemic species), and Sunflower bush. Santa Cruz Island has around 600 native plant species.
These cases, exhibit how island ecosystems are incredibly susceptible to disturbances, which can often be brought upon by the interference of humans. In the case of Catalina Island Fox, the introduction of a virus, possibly by a colonizer’s pet dog, is to blame for the collapse of a species. Santa Cruz’s population collapse was brought upon by the human introduction of pigs to the island, which facilitated the entry of yet another harmful invasive species. It is believed that in both instances, had humans not brought in these disturbances that such a collapse would not have occurred. Just as these collapses wouldn’t have occurred without human interference one can use Santa Cruz Island to “see” how different a landscape Catalina would have if it didn’t have the human introduced grazers still shaping plant communities on the island. As such these cases serve as a reminder that humans should exercise extreme caution when interacting with such isolated ecosystems, as they can be as fragile as they are unique and beautiful.
This post was written by Mariah Gill ’12 and Jefferey Nakashioya ’12 both seniors in Environmental Studies.
Carlos de la Rosa, Personal Communication/ Lecture
March 30, 2012
With the population in Los Angeles County fast approaching 10 million, it’s hard to imagine that just 19-25 miles off the Ventura coast, sits an unpopulated island of 96 square-miles that has remained in near pristine condition for thousands of years. As the largest of the Channel Islands, Santa Cruz is able to exist in such a preserved state largely due to it being positioned in one of the most biologically rich and productive marine regions in the Eastern Pacific – known as the Southern California Bight. Just south of Point Conception, portions of the southerly flowing California Current bend eastward towards shore into the Santa Barbara-Ventura Basin that separates the Northern Channel Islands from the mainland. There, this cold, nutrient-rich current converges with the warm, saline waters of the California Countercurrent as part of the larger ocean gyre system that’s created by the mixing of the California Current System around the Channel Islands. The combination of oceanic and climatic factors that make Santa Cruz so unique and rich in biodiversity have also helped lead to its protection and preservation, as 76% is owned by the Nature Conservancy, and the remaining 24% by the National Park Service.
Santa Cruz is not only the largest island, but it also has the highest peak (Picacho Diablo), which helps to create the many different microclimates on the island, also causing it to also have the greatest number of plant and animal species as well; 650 types of plants can be found here, and 480 of them are native to the island. The unique biogeography of the Southern California Bight has resulted in the Channel Islands being the exclusive home to 37 plant species; 8 of which are endemic to Santa Cruz alone, meaning they can be found nowhere else on the planet.
It is one thing to read descriptions of the natural history of Santa Cruz, but there is always a lot more to be gained personal experience and hands-on learning. Over the weekend, I was given the opportunity to camp at the field research station on Santa Cruz as part of a class field trip. The purpose of the trip was for observational analysis; it gave us a chance to visualize and discuss the relationships between the island’s many biogeographic characteristics, and to visualize concepts such as how variations in spatial distribution and types of vegetation are correlated to things like sun exposure and the gradient of the hillside. For example, in the following photo, you can distinctly see the how the concentration of vegetation increases as the gradient decreases and nears the low-lying center of the drainage basin – closer to the water table.
The slopes of the more distant mountains on the left are much steeper and higher in elevation, causing rainfall to drain rapidly. The resulting smaller concentration of plants found here are likely to be better adapted for faster water absorption and longer retention. The lack of vegetation could also be the result of a rainshadow effect that results from the sharp rise in elevation forcing moisture flowing onshore to condense and precipitate in order to rise over the mountains. In the absence of strong onshore winds, the lower elevations and valleys retain more moisture as fog, which can further be correlated to the increase in the abundance of vegetation shown in the photo. The hills on the right have a smaller gradient at a lower elevation. These factors allow the plants to accumulate more water and lead to the growth of the more herbaceous vegetation.
With so many valleys and rapid changes in elevation across the island, there are many resulting microclimates that contribute to the overall high level of plant diversity. One of our goals of the trip was to identify some of the island’s native and rare endemic species as we hiked across different parts of the island. Of the ones we observed, 15 native samples were collected and placed into flower presses. In the photos below, you can see my personal favorites, the Giant Coreopsis, Coreopsis gigantean (top), and the Island Morning Glory Calystegia macrostegia (below).
One of the focus areas of the trip was to compare Catalina and Santa Cruz islands in terms of climate, plant and animal abundance and diversity, and comparing the anthropogenic effects of settlements on Catalina to the long-preserved state of Santa Cruz. For example, due to the increased grazing pressure on Catalina from introduced species like deer, buffalo, and cattle, some of the undergrowth tended to evolve upwards over time in order to be higher out of reach. On Santa Cruz, the lack of grazers is reflected in the more shrub-like and spread out orientation of some of the vegetation. Over time, the grazers also led to differences in the distribution of certain plant species on the islands. The Giant Coreopsis is a good example of this because it’s preferred by many grazers; it is found growing abundantly on Santa Cruz in many different microclimates, whereas on Catalina it is mostly found growing on coastal bluffs – out of reach of the grazers. One of the interesting things we learned involved the complex relationship between the eagles and native foxes, as well as populations of feral pigs and spotted skunks. While they are damaging to certain types of vegetation, the role of these introduced pigs on the islands evolved over time to play a key part of the recovery efforts of both Bald and Golden Eagles on the islands, and reduce the predation pressure on some of the recovering populations of native island foxes.
As part of the restoration program, nesting pairs of eagles have tagged and monitored, and recently it was discovered that two bald eagle chicks have been born in nests on Santa Cruz Island. It was also the earliest that eggs had ever been laid since recover efforts began, and as of Wednesday, March 7th, a record 15 breeding pairs of eagles are known to be living among the Channel Islands, showing that they are making a solid recovery. In order to monitor the progress of the nests and increase awareness of their conservation efforts, live footage of 4 of the nests can be streamed below. There are two nests on both Catalina and Santa Cruz, and what’s even more exciting is that the eggs in these nests are all within a couple weeks of hatching.
I believe that stories like these help to highlight the importance of keeping the Santa Cruz preserved in its most natural state for future generations to see and learn from. It was a great hands-on educational experience and allowed us the opportunity to see what the island may well have looked like thousands of years ago.
This post was authored by Genivieve McCormick ’12 who is pursuing a BS in Environmental Studies and Mabel Nevarez ’12 who is pursuing a BA in Environmental Studies.
External media sources:
March 27, 2012
The island fox is one of the many endemic species that inhabit the Chanel Islands. The fox is the largest native mammal on the islands and was the top predator for thousands of years. It is believed that the island fox evolved from the gray fox, which came over from the mainland more than 18,000 years ago by rafting on pieces of debris from storms. Since the arrival of the grey fox, six subspecies of the island fox have evolved on the islands. The island fox is one-third the size of its ancestor. Urocyon littoralis santacruzae is the scientific name of the Santa Cruz Island fox.
While historically, the Santa Cruz island fox stood at the top of the island’s food web, a process known as hyperpredation caused ecosystem interactions to be restructured. Hyperpredation refers to a scenario in which an indigenous species is subject to increased predation from an exotic predator that is able to live because of availability of an exotic prey. On Santa Cruz Island, the indigenous island fox experienced increased predation from nonnative golden eagles that were able to colonize the island because of the abundance of feral pigs.
Pigs came to Santa Cruz Island in the 1800s when European settlers brought them over with sheep to serve as domestic livestock. Pigs that escaped or were let loose quickly established large feral populations on the island and reeked havoc on its ecosystem. Since pigs reproduce at alarming rates, large litters of piglets attracted golden eagles to the island in the 1990s. The piglets served as an abundant year-round food source that allowed the golden eagles to establish themselves on the island. Golden eagles would have become a problem sooner on the island, but a population of territorial bald eagles prevented them from establishing themselves. Unfortunately, by 1960, the bald eagle populations had disappeared because of hunting and DDT contamination.
While golden eagles prey on skunks, pigs, and foxes, the fox population has taken a disproportional hit in comparison to the other two prey populations. Pigs have the advantage of being able to reproduce throughout the year. They are also able to outgrow predation. Skunks avoid a lot of predation due to the fact that they are nocturnal creatures. Foxes, on the other hand, only reproduce once a year, are mostly active during the day, and can’t outgrow predation. In 1994, the island fox population was at around 1,5000. By 2001, the population had fallen to around 60. This amounts to a 95% reduction in population size in less than a decade. The Santa Cruz Island fox was declared an endangered species in 2004 by the U.S. Fish and Wildlife Service.
With the survival of the island fox at risk, a multi-layer approach was executed to return balance to the Santa Cruz ecosystem. This comprehensive eco-system recovery plan included captive breeding of the island fox, relocating the golden eagles that preyed upon the foxes, eradicating the feral pigs, and re-establishing the bald eagle on the island. Each component of this plan worked together to restore balance and successfully led to one of the fastest recoveries of an endangered species in US history. Since the foxes were first listed as federally endangered the population has grown by 20 to 30% annually. The total number of wild foxes has increased to over 410, with the island fox survival rate around 96% on the tracked and monitored foxes, all in less than a decade.
In order to boost the total fox population, a captive breeding program was established in 2001 on Santa Cruz Island. First wild foxes were caught, and breeding pairs were established. In 2005, 20 pups were born in captivity, with a total of 85 pups born over the programs six years. While captive breeding always brings about the issue of human interaction altering the behavior of wild animals, such a program was essential for boosting the total population in the wild. Additionally, the establishment of a successful breeding program represents a future for island foxes, because when numbers get exceptionally low, scientists can conceivably save the population from extinction by breeding pups in captivity. On advantage that the captive breeding program on Santa Cruz Island held over some of the other programs on other Channel Islands is that the large remaining wild population allowed for the program to increase the number of founders in captivity on a regular basis. If mating pairs were unsuccessful, they were able to bring in other foxes to breed with. This helped to increase the genetic diversity of those bred in captivity. These foxes were also vaccinated against canine distemper virus and rabies in order to limit the risk of disease causing a population threat down the line.
At first the pups released to the wild were quickly being eaten by the golden eagles, but as the Golden Eagle population on Santa Cruz was relocated to the mainland, the survival rate of pups increased dramatically. The relocation of the eagles was a crucial part of the fox recovery, as predation by eagles was identified as the cause of death for over 72% of the monitored foxes between 2000 and 2006. However, it was no simple task to be able to remove these eagles as they are legally protected by the Migratory Bird Treaty as well as the Bald and Golden Eagle Protection Acts. Once given permission to relocate these animals, 32 golden eagles have been captured and released on the east side of the Sierra Nevada Mountains. These magnificent birds are often captured using dug-in nets placed in areas that eagles frequent. The nets are baited with dead feral pigs or live rabbits, and radio-controlled to capture the eagle. The eagles are transported in large commercial sky kennels and are always released on the mainland within 24 hours. Today, Santa Cruz is thought to be home to less than 10 Golden Eagles that have continued to evade capture. Thanks to a very successful relocation program by the Santa Cruz Predatory Bird Research Group, the fox’s main predatory has been eliminated allowing for the foxes to recover.
However, relocating the current eagles to the mainland is an insufficient solution, without also removing the prey that first established the colony of golden eagles on the island. As a result, an intense feral pig eradication program has also taken place, resulting in the removal of over 5,000 pigs from the island by 2006. Today, no feral pigs remain. Santa Cruz sectioned off the island, and proceeded to hunt the pigs in each section, often shooting from a low-flying helicopter. Relocation of the pigs was not an option as Federal and State laws prevent moving these pigs to the mainland, due to potential diseases. This removal of pigs has also benefitted many native plants that were being destroyed by the pig population, such as the blue dick flower. The eradication of the pigs is thought to be the most important step in restoring the natural Santa Cruz ecosystem.
They also are working to re-establish the bald eagle, in order to prevent the golden eagle from recolonizing and re-threatening the fox in the future. The bald eagle used to occupy the island but was destroyed by high DDT levels off the coast. While the bald eagles eat fish, seabirds, and animal carcasses, they do not eat live foxes and therefore do not present a danger to the recovering species. Additionally, the bald eagles are extremely territorial, and since golden eagles and bald eagles hardly co-habitat anywhere, the increase in bald eagles would keep golden eagles from moving back to Santa Cruz. This effort is being led by the Institute for Wildlife Studies and the Montrose Settlement, who have released over 50 bald eagles since efforts began in 2002. For further reading on the bald eagle efforts, follow along at http://www.nature.org/ourinitiatives/regions/northamerica/unitedstates/california/explore/santa-cruz-island-bald-eagles-hatching-hope-2010.xml
Although the eco-system is certainly well on its way to recovering its natural balance, a few issues remain. The greatest concern is that the original depletion to merely 70 foxes created somewhat of a genetic bottleneck, reducing the overall genetic variability within the fox population. This may lead to the fox population being more susceptible to diseases and other threats that will impact all foxes with similar genetic traits. Additionally, there remains the question of how well the pups bred in captivity will be able to teach their young how to behave in the wild, since they lacked that form of training and it is believed that foxes parent their young through the first year. Whenever humans involve themselves in the raising of wild animals, there is a question of how that human interaction will impact the animal’s behavior in the long run. Outside of the fox problem, the Santa Cruz ecosystem is still threatened by non-native plants such as fennel overwhelming the natural vegetation which the animal populations rely on.
All in all, the eradication of feral pigs and relocation of golden eagles have allowed for the island foxes to recover at an unprecedented speed, making Santa Cruz Island an endangered species recovery success story.
This post was authored by Melissa Krigbaum ’12 a double major in Environmental Studies and Economics and by Alex Anthony ’12 majoring in Environmental Studies.