BT101 Merged PPT Handouts Lectures 86-150

Lecture 86

Coevolution:

The evolution of ecologically related species is sometimes coordinated such that each species exerts a strong selective influence on the other. This is Coevolution. Coevolution may occur when species are competing for the same resource or during predator–prey interactions. When populations of 2 different species interact, then changes in the gene pool of one species can lead to changes in the gene pool of the other species. Such changes can help both sides to become more competitive or can help to avoid/reduce competition. Biologists call this Coevolution.

One example of Coevolution is the relationships b/w some flowering plants & their animal pollinators. Insect- pollinated flowers are usually yellow or blue because insects see these wavelengths of light best.

Flowers pollinated by hummingbirds, are often tubular & red. Hummingbirds have a poor sense of smell but see red very well. The long beak of hummingbirds is an adaptation that allows them to reach far into tubular flowers.

Long-term interactions b/w bats & their prey such as moths and butterflies can lead to Coevolution, as the bats evolve traits that increase their chances of getting a meal & the moths evolve traits that help them avoid being eaten.

Lecture 87

Symbiosis:

Some of the best examples of adaptations arising through Coevolution come from two different species living in continuing, intimate associations, called symbiosis (Gr. sym, together bio, life). Symbiosis (‘living together’) is the term that has been coined for such close physical associations b/w species, in which a ‘symbiont’ occupies a habitat provided by a ‘host’.

In some instances, one member of the association benefits, and the other is harmed. In other cases, life without the partner would be impossible for both.

Common form of symbiosis are

o Commensalism · o Mutualism · Lecture 88 · Commensalism:

Commensalism is a symbiotic relationship in which one member of the relationship benefits, and the second is neither helped nor harmed. In tropical forests certain kinds of silverfish insects move along with columns of army ants to share the food obtained by the ants in their raids. The army ants receive no apparent harm or benefit from the silverfish. Epiphytic plants such as certain types of orchids & bromeliads attach themselves to trunks or branches of large trees in tropical & subtropical forests. These air plants benefit by getting a solid base on which they grow. They also live in an elevated spot that gives them better access to sunlight, water from the humid air & rain, & nutrients falling from the tree’s upper leaves & limbs. Their presence apparently does not harm the tree.

Lecture 89

Mutualism:

Mutualism is a symbiotic relationship that benefits both members. In mutualism, two species behave in ways that benefit both by providing each with food, shelter, or some other resource. For example, honeybees, caterpillars, butterflies, & other insects feed on a male flower’s nectar, picking up pollen in the process, & then pollinating female flowers when they feed on them.

In gut inhabitant mutualism, vast armies of bacteria in the digestive systems of animals help to break down (digest) their hosts’ food. In turn, the bacteria receive a sheltered habitat and food from their host.

Oxpeckers or tickbirds feed

on parasitic ticks that infest large, thick skinned animals such as the endangered black rhinoceros. A clownfish gains protection & food by living among deadly stinging

sea

anemones & helps protect the anemones from some of their predators.

Some other forms of mutualism are,

o Lichen · o Mycorrhizae · o Root nodules · Lecture 90 · Lichens:

A mutualistic association b/w algae & fungus in which both the partners get benefits from each other is known as lichen. Fungus are usually Ascomycetes or Basidiomycetes while the other partner is algae or cyanobacteria.

Growth forms of Lichens

1. Crustose 2. Foliose 3. Fruticose

Crustose:

A type of lichen that form a flat crust on the substratum & firmly attached to substratum.

Foliose:

This type of lichens have flat leaf like structures & are attached to substratum by thread like structures.

Fruticose:

This type of lichens have erect filamentous like outgrowths & possess vertical pattern of growth.

Benefits of Lichens:

•  Bio indicators
•  Ecosystem sustainability
•  Medicines
•  Animal food
•  Dye for clothes

Lecture 91

Mycorrhizae:

A mutualistic relationship b/w fungi & roots of higher plants by which both partners are get benefited. A very remarkable group of Ascomycetes fungi, Clavicipitaceae, grow in tissues of many species of grass. The fungal networks in Mycorrhizae capture minerals from the soil & transport them to the plants while in turn plants provides nutrients like sugars to fungus.

Major types of Mycorrhizae

1. Endomycorrhizas or Arbuscular mycorrhizas
2. Ectomycorrhizas
3. Ericoid mycorrhizas

Endomycorrhizas or Arbuscular mycorrhizas:

They are found in up to two-thirds of all plant species, including most nonwoody species & tropical trees. Fungus incorporates into cortical cells of roots of higher plant.

Ectomycorrhizas:

Ectomycorrhizal fungi form symbioses with many trees and shrubs, dominating boreal and temperate forests and also some tropical rainforests.

Ericoid mycorrhizas:

Ericoid mycorrhizas are found in the dominant species of heathlands (barren infertile lands) including the northern hemisphere heaths and heathers (Ericaceae) and the Australian heaths (Epacridaceae).

Lecture 92

Root nodules:

It is a mutualistic association b/w nitrogen fixing bacteria & roots of plants of legume family. The process of nitrogen fixation is done by different kinds of microorganisms.

Types of nitrogen fixing bacteria

Azobactor

- Free living aerobic bacteria

Clostridium

- Free living anaerobic bacteria

Chlorobium

- Photosynthetic bacteria

Thiobacillus

- Chemosynthetic bacteria Nostoc - Blue green algae A special vascular system develops in the host, supplying the products of photosynthesis to the nodule tissue & carrying away fixed nitrogen compounds to other parts of the plant. The nodule tissue provides shelter & carbon to bacteria.