Communities: How Do Species Interact? Chapter 27

Succession – the predictable change in the numbers and kinds of organisms in a particular area over time. Habitation of a completely new environment is called primary succession. Reestablishment of life after serious damage is called secondary succession.

Pioneer community – the first community in a succession. Climax community – the long-lived community at the end of a succession. “successional” communities – the intermediate communities between the pioneer and climax communities Pioneer and successional communities change over periods of 1 to 500 years. Climax communities last for more than 500 years.

Successional communities We tend to think primarily of plants since they are the producers. A deer carcass or a pile of dung can also have successional communities

Why does succession occur? Non-climax communities may degrade their environments Species in early successional stages can –Facilitate succession –Tolerate succession –Inhibit succession Pioneer communities always facilitate succession

The character of a climax community depends on abiotic factors such as climate, soil and terrain. May depend on the history of the region –Sequoia forests and fires

Are communities integrated or individualistic? Integrated communities consist of characteristic species that always interact with each other in predictable ways Individualistic communities are separate populations that merely inhabit the same habitat. Every community is unique.

Competition between trees? Mycorrhizae – soil fungus that supports the growth of certain plants Replanting issues

The First Law of Ecology Every species affects every other species. –Predator – prey interactions –Herbivore-plant interactions –Parasite –host interactions

A parasite consumes only part of its host, and does not necessarily kill the host. A “good” parasite would harm its host as little as possible so it would have a place to live. A predator usually kills its prey and consumes most of the prey’s body. –Use swiftness, intelligence, acute senses and sharp teeth to obtain food Herbivores use patience and a good digestive system.

How does one keep from being eaten? Camouflage or crypsis – blending into your surroundings

Plant defenses Mechanical defenses: –Waxy cuticle keeps bacteria and fungi out –Hairy or sticky leaves discourage tiny herbivores –Spines, thorns and prickles fend off larger predators

Plant defenses Chemical defenses – secondary plant compounds: –Terpenes –lipids- such as pyrethriods, essential oils, saponins, and gossypol –Phenolic compounds – carbon ring compounds -repel herbivores and pathogens or attract pollinators and fruit dispersers. Also lignin and tannins –Alkaloids –nitrogen containing compounds – nicotine, atropine, cocaine, morphine, strychnine and caffeine –Mustard oil glycosides – cabbage family

Animal chemical defenses Bees and wasps inject a powerful acid Skunk uses noxious chemicals Poison dart frog and the pitohui bird have deadly toxins in their skin

Warning coloration Keeps animals from being attacked repeatedly by warning off attackers These organisms have bright colors and memorable designs Harmless organisms can use mimicry –Batesian mimicry – when something harmless (and tasty) mimics something harmful –Mullerian mimicry – two equally harmful organisms develop the same warning patterns Protects both predator and prey

How do organisms live together? Symbiosis – “living together.” Parasitism – one species benefits and the other is harmed Predation - one species benefits and the other is harmed Mutualism – lichen – algae and fungus Commensalism – one species benefits, and the other is neither helped nor harmed.

Coevolution The acacia and the ants Bacteria and plants mycorrhizae

Competition One organism uses a resource that is in limited supply, negatively affecting another species’ ability to survive and reproduce. Organisms can compete for: –Territory –Prey –Other resources

Habitat – the place where an organism lives, along with the set of environmental conditions characterize that place. –Address Niche – the way an organism uses its environment –occupation

When there is a limiting resource and two different species compete directly for the same resource, the more efficient species will eliminate the other. – the competitive exclusion principle No two species can occupy the exact same niche in the same habitat indefinitely.

How can competing species coexist? Resource partitioning – dividing up the niche