Interaction in Ecosystems 1. Biotic Interactions 2. Symbiotic Relationships 3. The costs, benefits and consequences of interactions

Symbiosis A symbiotic interaction describes the relationships between organisms that are in direct contact A symbiotic interaction describes the relationships between organisms that are in direct contact Parasitism Parasitism Commensalism Commensalism Mutualism Mutualism

Parasitism Parasitism is a biotic interaction that is beneficial to one organism (the parasite) and harmful to another (the host) Parasitism is a biotic interaction that is beneficial to one organism (the parasite) and harmful to another (the host) Parasites may be Parasites may be Obligate – can only survive with this lifestyle Obligate – can only survive with this lifestyle Facultative – can be free living depending on the circumstances Facultative – can be free living depending on the circumstances

Parasitism cont… Most parasite – host relationships are stable for two reasons Most parasite – host relationships are stable for two reasons Obligate parasites do not benefit if they kill their hosts, therefore do as little harm as possible Obligate parasites do not benefit if they kill their hosts, therefore do as little harm as possible Hosts develop strategies to combat parasites. The parasites in turn evolve strategies to combat the host’s defences. As a result of this co-evolution many species specific interactions exist (i.e. host- parasite specificity). Hosts develop strategies to combat parasites. The parasites in turn evolve strategies to combat the host’s defences. As a result of this co-evolution many species specific interactions exist (i.e. host- parasite specificity).

Example - syphilis

Parasitism cont… Read the article ‘Syphilis in Renaissance Europe’ Read the article ‘Syphilis in Renaissance Europe’ What features of parasitism does the Syphilis – human relationship show? What features of parasitism does the Syphilis – human relationship show? What co-evolution was displayed in the relationship and how did this come about? What co-evolution was displayed in the relationship and how did this come about? What implications might this have for modern diseases such as those that reach epidemic or pandemic levels? What implications might this have for modern diseases such as those that reach epidemic or pandemic levels?

Parasitism cont… Parasite transmission Parasite transmission Direct contact – ‘JUMP!’ Direct contact – ‘JUMP!’ Resistant stages – Development of a stage that remains viable without the host. When the host is available again it resumes its lifecycle. Resistant stages – Development of a stage that remains viable without the host. When the host is available again it resumes its lifecycle. Vectors and Secondary hosts – vectors carry the parasite from 1 host to another. Secondary hosts can act as a means of wide dispersal (whereas the primary host acts as the main source of nutrition and development). Vectors and Secondary hosts – vectors carry the parasite from 1 host to another. Secondary hosts can act as a means of wide dispersal (whereas the primary host acts as the main source of nutrition and development).

Commensalism One species derives benefit and the other species is unaffected One species derives benefit and the other species is unaffected

Mutualism Both species in the relationship benefit from the interaction Both species in the relationship benefit from the interaction