Päiväkirja-arkisto kohteelle marraskuu 2023

marraskuu 10, 2023

Random tidbits of information from the 10th California Islands Symposium

6–10 November, 2023; Ventura Beach Marriott

Apologies for my notes below – terribly random and incomplete, missing "main punch lines" from most of what I listened to. Also missing the names of speakers... I found the 15-minute time slots so hectic and fast-paced that I barely could keep up...

Adam G. Dillon – Anthropogenic Restructuring of Trophic Network
and populations of Spotted Skunk and Island Fox

1990s DDT crash of Bald Eagle
was trigger (in combination with introduced ungulates) that allowed for invasion of Golden Eagle

(ranch ungulates were removed, but deer and boar remained once switch to GE apex occurred).

44 GE relocated 2000-2007
during this time foxes were being captive-bred. So for a short time, Spotted Skunks were the apex predator.

2012 – Last known GE depredation of Island Fox on northern islands.

Spotted Skunks weigh 500-900 grams

1892 first modern written report of their existence on the islands

1973 – Lyndal Laughrin was first to publish a scientific report of the existence of skunks on the island (late!)

Mate in fall, birth in spring –—> Delayed implantation

2016 “Skunk Renaissance” – new working group formed:
Calypso Gagorik studies fox home ranges, Juliann Schamel (dietary partitioning) and Adam Dillon (food web dyamics)

Fox and skunk population abundances are virtually directly inverse – indicative of interference competition
Aggressive interactions? If so, expectation would be skunk avoidance of foxes.

Fox peak activity around dusk; skunk activity peaks around midnight

Skunks use low shrubs and rugged terrain to avoid foxes

How and when did skunks colonize the islands?

Both populations (Rosa and Cruz) can be traced to a single maternal ancestor!
Split between islands and mainland and between islands happened at same time.

Early Holocene colonization, just prior to breakup of Santarosae (at time, 4-7 mile channel width).
Rafting or anthropic (Chumash) dispersal. NOT Euro dispersal.
Pattern of dispersal to northern islands directly mirrors foxes. Single maternal ancestor, same timing.
Full species status for island skunks?

Skunks have larger home ranges than foxes, but only use small parts of it at a time (seasonal).

Ellie Armstrong – measuring and managing bias in interpretation of genomic data in Canidae

“Genomics is becoming an integral part of conservation management.”

Urocyon is 10-14 million years diverged from rest of Canids – basal lineage.
Domestic dog is 2n=78
Urocyon 2n = 66
Arctic Fox variably 48-50 (!!!!)

Island foxes are extremely territorial, and their home range size is strongly negatively density-dependent;
having shrunk 83% (!!!!) on average in a decade of population recovery (now approaching carrying capacity). Virtually no overlap in home ranges either at low or high density.

San Clemente Island:
NE side of island is moister, SW side is drier – on NE side snails grow larger; little intermediate habitat

Micrarionta maxima and gabbi – two similar congeners – distinct-ish by geography and habitat; distribution of shell size.

Genetics show full intergradation: 1 species. gabbi is a forma; a distinct-looking one, but no more.

David Headrick — 80 year history of Cochineal-Opuntia biocontrol on Santa Cruz Island
Sheep came with Spanish colonists, cattle 1851, pigs 1854, fennel introduced 1886

Overgrazing turned grasslands into habitat for Opuntia. Stanton controlled his cattle grazing and corralled sheep, but Opuntia expanded and Stanted searched for a method of control. AJ Nicholson (Australia) suggested use of Cactoblastis cactorum (S. American moth). Stanton asks Harry Scott Smith (Father of Biocontrol; UC Riverside), who declined – fear of havoc on mainland Opuntia.

Smith suggests cochineal instead – obtained permission in 1940, releases begin.
Cochineal became fully established only in 1951 at the ranch.

In 1958, they started hand-spreading cochineal-infested pads around the islands.
Cactus reductions begin to happen by 1961.

Don Ricker, UC Riverside, begins biannual photosurvey to document cactus decline through 1980s. In many areas it has incredibly strong effects. But by 1970s – cactus decline slows down due to more-susceptible O. littoralis being mostly knocked back and resistant O. oricola left over.

Cactus declines continue into modern times, with serious consequences – e.g. reduction in safe Spotted Skunk denning sites.

Study in 2018: Four orders and families of CA insects that are predators on cochineal.

  1. Ladybird
  2. Brown lacewing Sympherobius barberi
  3. Leucopis sp. Chamaemyiidae aphid fly (most common predator in 2018)
  4. Caterpillar! Laetilia coccidovora – reached island in 1970s

Cochineal has no known parasitoids!!! However, their predators do! e.g (Pachyneuron eros) (Pteromalidae)
Currently, increase in cochineal-predator parasitoids may be shifting the balance back towards cactus decline!

In the last decade, cochineal has dispersed to Anacapa; worry is that it will reach Clemente.

David Headrick – Gall forming insects of Santa Cruz Island
Known oak galls on mainland - 136
33 undetermined

15 of known on SCI
4 unknowns from mainland on SCI
2 not known from mainland.

Torymus californicus – ovipositor 10 mm long (twice as long as body) – correlates with oviposition when gall has grown large. Some parasitoids with short ovipositors deposit eggs

1 gall inducer and 3 inquilines, but all Cecidomyiids!

Up to five species of gall on a single oak leaf!

Orrock — Rodents + Sin Nombre Virus (Hantavirus)
Deer mice primary host

Sin Nombre is what we mean when we say Hanta
35-50% mortality, but difficult to contract

Inhalation of aerosolized urine/airborne fecal dust. Exposure to saliva from a bite.
Mice remain viral carriers even after they clear the acute infection.

Some islands had 0 SNV, others had huge prevalence (SCR had 60-70%)

After ’14-’17 surveys, SNV absent from 5 islands.
Adult males twice as likely to have SNV (probably due to aggressive interactions/biting)
Significant annual variation in prevalence

Long-term data is "addictive" because it positions you to interpret consequences of unpredictable disturbances: Fire, drought, biotic change

Burned habitats have significantly higher prevalence of SNV in year 0, 1, and 2 after fire.
Pattern driven by male mice. SNV degrades rapidly with UV exposure.

Bites much more risky than feces!

“Island Syndrome of reproduction”
Larger adult body mass
Higher density and survival
Reduced aggressiveness, litter size, and dispersal

Life history consequences of island dwarfism in reptiles?

Gopher Snake and Alligator lizards are much smaller on the N. ChIs islands than mainland, but less pronounced difference for Yellow-bellied Racers.

Side-blotched and Fence Lizards do not show this pattern.

Do dwarf reptiles have smaller clutches on islands?
– Alligator had fewer eggs, mostly because smaller. Fence lizards have fewer eggs even when accounting for body size. Racers had same or more than expected for their size, but maxed out at around 4-5.

Do dwarf reptiles reproduce at smaller size on islands?
Both racers and alligator lizards had lower mean SVL of reproductive individuals.

Plenary 9 Nov 2023
Exequiel Ezcurra — Islands of Sea of Cortés
San Pedro Martir island – Cardon cactus dominant
Isla Rasa (note, “S” spelling – flat, low-lying, not “Z”, a genetic lineage)
“Guano valleys” – since seabirds have been nesting there since the Pleistocene, much of the sediment is guano.

Julkaistu marraskuu 10, 2023 07:30 IP. käyttäjältä leptonia leptonia | 1 havainto | 1 kommentti | Jätä kommentti