Species Interactions

Examples

An example: schistosomiasis, many endoparasites have complex life cycles involving two hosts The blood fluke parasitic trematode Schistosoma mansoni infects 200 million people around the world, causing schistosomiasis, it requires two hosts: snails and vertebrates. Many parasites manipulate their host's behaviour to allow better transmission between hosts. E.g. hairworms and crickets (Orthoptera). Plants can be partial or total parasites of other plants. A hemi-parasitic mistletoe (Ileostylis): steals from the host root system, but makes its own food (it is green). A holo-parasite (broomrape, Orobanche minor) steals both water and sugars from the roots of other plants.

Herbivory

Animals (herbivores) eating plants. Mostly resembles parasitism, in that the host plants are usually weakened rather than killed. Can be ecto-and endo-herbivores. Very important and widespread. E.g. a deer, a plant ectoparasite / herbivore. A leaf minor, a plant endoparasite. A sooty beech scale insect, a plant parasite.

Commnesalism (+/0)

Commensalism = one species benefits, no cost to the other. Maybe not very common. Example: Cattle & egrets. Egrets get insects, cattle not affected. Another example fantails and humans, fantails get insect with no cost or benefit to humans.

Competition (-/-)

Competition = an interaction between individuals, brought about by a shared need for a limited resource, and leading to lower growth or survival of at least some of the competing individuals. Intraspecific competition = within the same species. ...plays an important role in population regulation.; Interspecific competition = among different species. ...important in determining community structure.

Types Of Species Interactions

In terms of effect on species 1 and species 2. Mutualism - positive & positive. Predation, parasitism, parasitoids and herbivory are all positive & negative. Commensalism - neutral & positive. Interspecific competition - negative & negative.

Conclusions

Interspecific interactions can be classified by: who wins and who loses, duration and lethality of effects. Parasitoids are like (fill in conclusion from lecture here), Competition is very important for structuring niches.

Spite (0/-)

Not usually mentioned; may not exist. (1) "Biotic disturbance" - animal walking trails, cowpats. (2) Spiteful interactions - Humans squashing spiders, magpies harrassing other birds, and cyclists. Doesn't affect native birds (Morgan & Innes report for regional councils). Probably some (small) cost to the harrassing animal, so -/-. Thus, may not be any examples.

Parasitoids

Parasitoid adult lays an egg inside the host; the larval parasitoid then eats the host completely from the inside out, inevitably (but sometimes slowly) killing it. Extremely numerous and successful. Seems very gruesome to us. Parasitoid (a golden hunter wasp) with a paralyzed spider. The wasp seals the living spider in a chamber with an egg laid inside it. The larval wasp eats the spider from the inside, but leaving the vital parts (heart etc) till last. Parasitoid wasp attacking snow tussock flower midge at Mt Hutt. Wasp egg stays dormant in larva while it feeds to full size, then eats it. Parasitoids can be classified as like parasites, or like true predators. What do you think is the more useful approach?

Niche Evidence - Changed Niche Dimensions

Realised niche = range to which a species is confined by competitors or predators (and the range of conditions under which an organism is observed in nature). Fundamental niche = range which a species could occupy in the absence of interference from other species. A change in realized niche = good evidence for competition. Kokopu exclude mudfish. Brown mudfish grow well in less acid, higher oxygen, permanent ponds. But Banded kokopu do better there, exclude them. If kokopu present, mudfish absent. Kokopu absent in temporary ponds.

Niche Evidence - Character Displacement

Defined as more divergent traits when the species occur together (sympatric) than when they occur apart (allopatric) for the same two species. E.g. beak size variation between populations of two Galápagos finch species.

Predation (+/-)

Eating another species, but there are several subtypes. True predation - One species (the predator) kills another (the prey) straight after attacking it. Predation (who eats whom) is probably the most important group of ecological interactions. E.g. rats killing fantails, wolves killing moose, stoats killing rats, mice and birds. At least four plant groups eat animals; Venus fly trap 1 species, Sundews 194 species, Pitcher plants >100 species and 4 families, Bladderworts 233 species.

Parasitism & Herbivory

Effect usually not lethal or only gradually so, remove only part of an individual. One species (the parasite) feeds on another (the host) but usually does not kill it. Endoparasites = organisms that live within the host e.g. endoparasite deformations in rare galaxiid fish, spinal malformations in adult Galaxias anomalus with infections of Telogaster opisthorchis, ectoparasites = parasites that feed on the external surface of the host e.g. sandfly. Parasites are extraordinarily numerous, and extraordinarily important. There are both animal parasites and plant parasites, feeding on both animal and plant hosts.

Mutualisms (+/+)

Facultative mutualism = members can survive with or without the mutualism; links can be specific or quite general. E.g. plant/mycorrhizal fungus, ant/aphids (ants get sugar, aphid gets protection), plant/pollinator for dispersal and a feed (e.g. Tui pollinating NZ flax), plant/frugivore. Obligate mutualism = each species can't survive without the other; usually very specific. totally obligate, or nearly so: coral (anthozoan & alga), lichens (fungus & alga) where the alga gets a home and the host gets fed. Another example is human cells and mitochondria. Mutualisms are very common and very important.

Niches And Competitive Exclusion

Gause's competitive exclusion principle: two species competing for the same limiting resources (i.e. niches) cannot coexist in the same place. Ecological niche = sum total of a species' biotic and abiotic resource use. Niche overlap indicates that competition could occur because some of the resources are shared. BUT...What evidence do we have for this? Resource partitioning in New Zealand birds on a tree, Fantail - flying, Grey Warbler - canopy, Brown Creeper - upper, Bellbird - mid level, Rifleman - trunk and Robin - ground. Same pattern in Darwin's finches with the different food types.

Varying Predator Interactions

They typically vary in duration and lethality. Long duration and high lethality - parasitoids. Long duration, low leathality - parasites. Short duration, high leathality - true predators. Small duration small lethality - herbivores. Life is not always simple. Many animals eat several types of food. Omnivore= eats both plants and animals. Possum and ship rat eating song thrush chicks. Both are omnivores.