Channel Islands Santa Cruz island is the largest of the six channel islands off

Question

Channel Islands

Santa Cruz island is the largest of the six channel islands off of California’s coast, and is entirely made up of conserved land and National Park administered land. The island is approximately 250 km^2 and is home to approximately 140 land bird, 11 mammal, 3 amphibian, and 5 reptile species. The next biggest island, Santa Rosa, is ~200km^2 and is home to approximately 100 bird, 3 mammal, 2 amphibian, and 3 reptile species.

Pigs, Eagles & Foxes - Channel Islands Case

Golden eagles, feral pigs, and insular carnivores: How exotic species turn native predators into prey by Roemer et al (citations removed from text)

Pigs produce a large number of piglets annually, are capable of producing young in any season, and escape predation by growing beyond the size range typically preyed upon by eagles (0.5–4 kg). In contrast, less than 60% of mature female foxes on Santa Cruz Island annually produced pups and with a litter size of, on average, ~1.5 pups (one litter per year). Skunks are also affected little, because they behaviorally avoid predation by being almost entirely nocturnal. On Santa Cruz, skunks were never active during the day (n=107 locations), whereas foxes were active in 60% of 592 diurnal locations.

Does the Order of Invasive Species Removal Matter? The Case of the Eagle and the Pig by Collins et al 2009 (citations removed from text)

Previously, it had been suggested that foxes may have responded to the intense predation by reducing diurnal activity, either through experience (e.g., escaping a predation attempt) or because eagle predation acted as a selective force removing foxes that were more active during the day. More recently, a comparison of activity patterns prior to and after the colonization of the island by eagles showed that wild foxes remaining on the island during the period of golden eagle occupation did reduce their diurnal activity.

Current Status on Santa Cruz Island

Recovered. Captive breeding ended in 2008 for the Santa Cruz Island Fox (Urocyon littoralis santacruzae) and all foxes were returned to the wild. Survival remains very high, and the population has increased steadily. Some areas now show less increase (fewer pups) as the population nears historic density.

Santa Cruz Island

Adult Fox Population

1993 - 1406

1997 - 1073

1999 - 527

2001 - 137

2006 - 204

2009 - 1150

2015 - 2170

Santa Cruz Island Fox Populations

Santa Rosa Island Populations

1. What was the per capita rate of population change for foxes on Santa Cruz Island in 1999? (Assumptions: Male to Female ratio = 1:1 and ~290 foxes died that year.)

Explanation / Answer

Ans- the initial population size- 527

Population change - 527-290 (because 290 fox died in that year so subsequent population - 237

Population change rate= absolute change/ initial population ×100

= 290/527 ×100

= 0.5502×100

= 55.02%

So the population change rate= 0.5502 or 55.02%

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