sagacious.us
San Francisco Forktailed Damselfly
Ischnura Gemina
I did a little research on this particular damselfly for a biology class at City College a few semesters ago. Because information about this damselfly is relatively hard to find I thought I would share my sources and what I learned about this fantastic little creature:
- What kind of food(s) does it eat? Are its food requirements specialized (one or a few plants and/or animals) or greens?
The San Francisco Forktail Damselfly is a voracious predator in all of its stages of life, as a nymph and as an adult. (Bakker, Borrer 1987) Nymphs are agile swimmers and are able to catch and eat any aquatic animal that is sufficiently small, including small fish and insect larvae, they are known to feed on mosquito larvae when present, they are generally opportunistic eaters. (Essig)
Adults, as nymphs, are opportunistic predators, catching small insects in mid flight with a long claw like labium, including gnats, mosquito and similarly sized flying insects. (Essig, Klots 1972)
- What is the habitat or community type(s) that this animal species needs to grow, survive, mate, and have offspring?
Because the nymphs are entirely aquatic, communities of damselflies (of all types, not just I. gemina) are centered around permanent water, generally small, slow moving or still ponds and streams.
Males are territorial and will defend areas of water that are good oviposition sites. Such sites must have reeds or grasses coming from the water (for nymphs to climb up to perch on while they molt and transform into adults), waters also must be reasonably free from predators such as fish. (Choe)
As the SF Forktails are poor fliers, genetic diversity can only be maintained by high population densities, numerous nearby small populations is not sufficient, and because of the territoriality of the males requires large areas of suitable ovipisition sites.(Choe)
- What other species are required for the species to complete its life cycle? ie. Food species, pollinators, etc.
Because the SF Forktail is an opportunist in all of its stages of life it is not particularly dependent on any one species as a food source.
- What other species rely on this species to survive? (i.e. predators, herbivores)
While the SF Forktail may be a prime food source for some species of bird or fish, I did not find any such references. Though I should mention that it is preyed upon by birds and fish (Bakker), perhaps just not exclusively.
- What was this species historical range ro gergraphical distribution and what is its current range or geographical distribution?
The range of the SF Forktail historically and presently is from Marin to Santa Cruz counties, specifically in areas with small springs and shallow slow moving streams and ponds. (City of San Jose) While the full geographic range of the SF Forktail seems to be basically the same, the available habitats within that range are becoming scarce.
- Why is this species in need of having its habitat restored (i.e. why has this species numbers and/or habitat declined?)
The SF Forktail is a very poor flier (Borror), so the females are unable to travel great distances to seek mates and maintain genetic diversity, therefore regions with many good ovipositon sites must be in close proximity. (Choe) The SF Forktail also prefers areas with nearby sunny fields or low vegetation which provide areas to perch (City of San Jose), habitat for flying insects which are the main food of the adult Forktail and which provide some cover from predatory birds. With urban sprawl having all these factors in one place is becoming a rarity.
- List and describe FIVE life history characteristics of your species that would help inform what its habitat requirements might be. (examples: mating time mating courtship requirements , number of offspring per effort, etc...)
- Because males will defend multiple individual females while they are in his territory, genetic diversity is increased with greater population density as the females will need to travel between different mates(Choe), thus habitats must be large enough to support multiple distinct territories by, yet compact enough to allow the females to visit the multiple territories.
- Reproductive life cycle of SF Forktail is relatively short, being only a couple weeks, permanent fresh water must be available for oviposition, and it must be around for the several months it takes for the nymphs to mature in it before they finally molt and become adults. This same habitat also provides more abundant food sources like mosquitoes and other flying insects which are important food sources for the SF Forktail through every stage of its life.
- Eggs laid during spring and summer are inserted into plant tissues with a needle like 'ovipositor' (Essig), thus suitable reeds and rushes must be present in for a habitat to be suitable for the SF Forktail. These same reeds are required by the nymphs when they need to climb from the water for their final molting when they become adult damselflies (Klots 1972) thus the water sources must be essentially permanent year round. This is already a rarity in California, and is becoming more so as non native trees are introduced to some wetlands and others are being built upon.
- Because females may select mates based on the sites they wish to deposit their eggs, as opposed to selecting them based on inherent qualities of the would be mate, habitats must be suitable to encourage copulation. (Choe) Interestingly, and only tangentially related here, a female may mate with a male so that he will allow her to use his territory to deposit her eggs, however because she can select which sperm to use to fertilize the eggs she deposits this does not guarantee that the eggs laid in one male's territory will have been fertilized by him!
- The SF Forktail prefers areas with nearby sunny fields or or low vegetation which provide areas to perch (City of San Jose), habitat for flying insects that provide food for the adults and some cover from birds hoping to feed on them. (Forgive me, this is also the answer to #6 above) This coupled with their poor flying ability means that suitable water must be located near the sunny meadows or lowly vegetated lands.
