Changing seasons

This pic is from the same spot throughout 2007-2008. You can see the winter rains bring green life to the coastal sage plant community. Soon the heat of summer returns bringing with it death and destruction...or whatever.

Native Harvester ants

Harvester ants were abundant along the coast but have largely been displaced by the invasive Argentine ant. Pogonomyrmex subnitidus still occur in Torrey Pines State Park in San Diego along the coast. These ants collect seeds (hence the name) and the picture above left shows a nest. Scattered all about the nest are seed husks (right pic-nest hole in center) and abandoned refuse the ants carry from the interior to the surface. The pic below shows a pogo being attacked by another California native Dorymyrmex insanus (the small black ant). The pogo has a seed in its mandables and the dory is trying to steal it or is just raising hell. These ants primarily eat seeds yet apparently like most animals they appear to be opportunists. The following video shows a harvester ant attacking a moth larvae during a moth outbreak. During the spring of 2008, these moth larvae could be found everywhere crawling all over the ground and eating vegetation. This moth outbreak was followed by a carnivorous Carabid beetle outbreak refer ed to as a numerical response. The abundance of these caterpillars was a great source of food for many carnivorous insects.

Messor pergandei is another harvester ant found in the deserts. The following video is of a foraging trail in the Anzo Borrego Desert. At a certain point in time, the signal is given to launch a "seed run" (like a beer run..) along "trunk trails" where the ants pour out of the nest and head off in a column like an army on the move. They soon reached their destination and spread out -every ant for herself! With plunder in mandible, they soon return to the nest. It was striking to see this large column of onyx ants cross the trail that just 10 minutes earlier was quiet and abandoned.

Harvester ants lend themselves to a classic experiment. Optimal foraging theory predicts that an animal will maximize energy gain per unit time when foraging. You can test this easily. If you find a nest, you can place seeds (or oatmeal) of varying sizes at different intervals from the nest.

I was assaulted by a fly in the above clip.

Wikipedia : Messor is a myrmicine genus of ants with more than 100 species, all of which are harvester ants; the generic name comes from the Roman god of crops and harvest, Messor. The subterranean colonies tend to be found in open fields and near roadsides, openings are directly to the surface. The Vessomessor genus was recently added to messor adding 8 more species.
Colonies can achieve huge sizes and are notable for their intricately designed granaries in which seeds are stored in dry conditions, preventing germination. The structure of Messor spp. nests is complex and the genus on the whole is one of very accomplished architects.
Messor spp. are polymorphic and have a distinct caste of macrocephalic dinoergates [big headed workers] whose role is of carrying and cutting the large seeds which comprise much of the colonies' subsistence.
Equipped with a tough shining cuticle, Messor spp. are slow moving and form long, seed-carrying runs. Colonies tend to be monogynous and are founded by a single queen alone

Exploitation

Nectar is provided by flowers to help facilitate the dispersal of pollen by attracting pollenators. Insects and Angiospersms (flowering plants) have a shared evolutionary history and have coevolved with each other. Here we see an ant (Myrmecocystus sp.) drinking the nectar of Isomeris "bladder bulb". The plant is losing out as ants are notoriously poor pollenators. This is an example of exploitation found in nature.

The Purple flower is a species of Mallow being exploited by Formica moki, an ant found in San Diego County. Below is the intended recipient of the nectar fast asleep after a long night out!

Ants recruit to San Diego Barrel Cactus EFNs

The San Diego Barrel Cactus is found from N. Baja California, Mexico to the edge of San Diego County primarily along the coast in Coastal Sage scrub. This barrel cactus maintains extra-floral nectaries (EFNs - nectaries outside of the flower; floral nectaries attract pollenators in pollenation mutualisms). EFNs on the barrel cactus are modified spines that secrete carbohydrates. EFNs attract ants to protect the cactus from harmful herbivores (bugs). EFNs are found on a variety of plants not just cacti.

The following videos are of different ant species that occur on the cactus and presumably protect the cactus in exchange for a carbohydrate reward offered by the EFNs:

As you can see, these ants vary in their ability to protect the cactus. The larger Camponotus sp. does not recruit to food sources (apparently) as readily as Tapinoma sessile.

Defensive mutualisms 1

Defensive mutualisms are common in nature and are readily found in ant-plant associations. Typically these associations involve the plant offering the ants food directly (carbohydrate exudates) in exchange for protective services. These relationships are constantly evolving and should be thought of as "mutual exploitation" rather than casual friendly relations. Plants will skip out on offering valued resources if there was no benefit and vice-versa.

Sometimes, other insects (Hemipterans) harm the plant by sucking plant phloem but excrete honeydew which attract ants. Renowned biologist Janzen (1979) proposed that plants that haven't yet evolved carb. exudates directly to offer ants, will tolerate these harmful bugs as they attract ants that scare away much more damaging insect herbivores. Janzen proposed the maintenance of the herds of scale insects and other honeydew exuding homoptera is more or less a fixed cost for the plant, the equivalent of maintaining secondary defensive compounds and alkaloids (think of poison oak). The ants protect the trees from herbivores, vines, and mammalian browsers. A removal experiment supported as much. Below is a video of a native ant Tapinoma sessile interacting with aphids. Visible in the movie are aphid "mummies" or aphids that have been destroyed by parasitoids (insects that live inside the host and eventually kill the host - like in that movie Alien). The parasitoid was most likely a wasp that had oviposited its egg into the living aphid. The mature wasp emerged and left behind the hollow mummy.