Maarg Manthan · Topic 3.7

Ecotone

Environment & Ecology › Population Ecology and Species Interactions · Topic 3.7

An ecotone is the zone of transition between two adjacent ecological systems, such as a forest and a grassland, a river and the sea, or a pond and the land, in which the characteristics of both systems overlap and mix. The word comes from eco, house, and tonus, tension. An ecotone may be narrow and sharp, like the edge of a forest next to a field, or wide and gradual, like a savanna between forest and desert. It generally has a greater number of species and a higher density of some species than the adjoining ecosystems, a result called the edge effect, and it contains edge species that are restricted to it. When the transition is a gradual change of a factor along a gradient, such as altitude, it is called an ecocline. Ecotones are sensitive indicators of change.

5 min read · UPSC Prelims · Environment & Ecology · Population Ecology and Species Interactions

At a Glance

Meaning Transition zone
Effect Edge effect
Special species Edge species
Gradual change Ecocline
Indian examples Sundarbans, Terai
Exam link UPSC Prelims, Environment & Ecology: Population Ecology and Species Interactions

Where Does It Fit?

This topic follows the account of species interactions. It looks closely at the junction between ecosystems, where interactions among species of two communities occur, and prepares for the later macro on terrestrial and aquatic ecosystems. Previous topic: Interaction Between Species. Next topic: Endemic Species, Keystone Species, Indicator Species, Invasive Species.

What Are the Features of an Ecotone?

Feature	Details
Meaning	A transitional area between two biomes or ecosystems. Examples: mangrove (land and sea), estuary (river and sea), grassland and forest border, marsh, riparian zone and the tree line
Width	A narrow ecotone changes abruptly over a short distance; a wide ecotone changes slowly over a long distance
Species composition	Contains species of both neighbouring ecosystems plus edge species that need the mixture of conditions
Edge effect	Greater diversity and density of organisms at the junction, as it offers resources of both communities
Negative edge effect	Predators, nest parasites and alien species move in from the edge, harming interior species
Ecocline	A gradual change in conditions along a gradient, such as altitude or salinity, without a sharp boundary
Dynamic	Ecotones shift with climate, fire, grazing and human land use

What Are the Examples, Importance and Threats?

Mangrove ecotone: between land and sea, rich in fish nurseries; the Sundarbans, Bhitarkanika and Pichavaram
Estuarine ecotone: where freshwater mixes with seawater, as at the Hooghly estuary and Chilika lagoon; high nutrients and productivity
Terai: a moist belt between the Himalayan foothills and Gangetic plains with grassland and forest; home to rhino and tiger
Forest-grassland ecotone: savanna
Tree line: where mountain forest meets alpine meadow, sensitive to climate change
Riparian zone: bank vegetation along rivers; filters pollutants and shelters wildlife
Importance: high biodiversity, nurseries for fish, filters, corridors for animals, and sensitive early warning of climate change
Threats: land clearing, aquaculture in mangroves, dams, roads and climate change

What Else Should You Remember?

Ecotone origin: a term introduced by F E Clements in 1905
Edge species: birds like thrushes and warblers prefer forest edges
Human-made edges: roads, farm borders and power lines create sharp edges
Fragmentation: too many edges leave little interior habitat
Interior species: species that need deep forest and avoid edges
Minimum patch size: conservation sets large cores with buffers
Buffer zones: outer areas of a protected area act as ecotones with human use
Corridors: strips of habitat that connect patches
Ecotone monitoring: used for studying climate impacts
Coastal ecotone: sand dunes, salt marshes and mudflats
Wetland ecotone: wet meadow zones act as filters
Ecotone and fire: fires shift forest-grassland boundaries
Ecotone and grazing: grazing keeps grassland open
Alpine ecotone: krummholz stunted trees at the tree line
Ecotone shifts: Himalayan tree lines are creeping upward in some places
Biosphere reserves: core, buffer and transition zones, as in Biosphere Reserves, Sacred Forests, Sacred Lakes
Link: earlier treatment of edge effect is in Stratification, Ecotone and Ecological Dominance
Link to estuaries: see Coastal and Wetland Ecosystems in the later macro
Caution: some ecotones, such as degraded edges, have lower value, so quality matters
Ecotone in a pond: the littoral zone where water meets land has reeds, frogs and insects from both worlds
Ecotone and agriculture: farm borders with hedges support birds and pollinators
Estuarine value: estuaries nurse young fish and prawns and support fisheries
Edge management: retaining native vegetation along streams and roads keeps the benefits of edges
Research use: ecotones are used to test ideas on boundaries, species ranges and climate change
Seasonal ecotones: floodplain edges change with the monsoon, creating a moving transition zone
Ecotone and people: traditional communities often live at ecotones and use both resources, which can cause conflict with wildlife

Why Does It Matter for the Exam?

Meaning: transition zone
Edge effect: more diversity
Examples: mangrove, estuary, Terai
Current affairs link: tree line shift
Common errors: saying ecotones have fewer species or confusing ecotone with ecocline

As an analytical point, ecotones combine high biodiversity with high sensitivity. Managing them with buffers and corridors, and monitoring them for early signs of climate change, is a low-cost way to protect larger ecosystems.

Why Is This Topic Important?

Meaning Junction
Effect Diversity
Use Early warning

What Came Next?

The next topic covers endemic, keystone, indicator and invasive species. Next topic: Endemic Species, Keystone Species, Indicator Species, Invasive Species.

Key People and Terms

Ecotone Transition zone
Edge effect Higher diversity at edge
Edge species Species found at edges
Ecocline Gradual gradient
Riparian zone Riverbank zone
Interior species Need deep habitat

Exam Corner

Points to Remember

Ecotone has more species through the edge effect.
Mangrove = land-sea ecotone.
Terai = Himalaya-plains belt.
Ecocline = gradual gradient.
Term used by Clements, 1905.

Do Not Confuse With

Ecotone and ecocline Zone of overlap versus gradual gradient
Edge species and interior species Need edges versus avoid edges
Positive and negative edge effect More diversity versus harm from predators and aliens

Memory Hook

Where two worlds meet, species meet more; guard the edge, but not too much of it.

Mains Angle

Questions ask for features and examples. These points help.

Features Edge effect
Value Biodiversity
Threats Fragmentation

A Question You May Face

An original practice question, not a past paper question.

“What is an ecotone? Discuss its characteristics, ecological importance and the threats it faces with Indian examples.”

How to Answer

Define Ecotone.
Features Edge effect.
Examples Mangrove.
Threats Clearance.

GS Relevance

Prelims: definition, features, edge effect, examples, ecocline. GS Paper 3: ecology and conservation.

Frequently Asked Questions

What is an ecotone?

An ecotone is a transitional zone between two different ecosystems or biomes, such as a forest and a grassland or a river and the sea, in which the characteristics of both overlap. It may be narrow or wide and generally has a rich mix of species from both neighbouring areas and some special species of its own.

What is the edge effect?

The edge effect is the tendency for a greater variety and density of organisms to occur in the ecotone between two habitats than in either habitat alone. It results from the availability of resources and shelter of both ecosystems, though edges can also expose interior species to predators and invaders.

What are edge species?

Edge species are species that live mainly or only in ecotones, the junction of two habitats, and need the conditions found there, such as certain birds that nest in forest cover but feed in open grassland. They tend to increase when edges are created by clearing, unlike interior species that need deep forest.

What is the difference between an ecotone and an ecocline?

An ecotone is a zone of transition where two communities meet and mix, often with a distinct set of species. An ecocline is a gradual gradient of change in an environmental factor, such as altitude, salinity or temperature, across which species change continuously without a clear boundary between communities.

Why are ecotones good indicators of climate change?

Ecotones lie at the limits of the tolerance ranges of the species of both neighbouring ecosystems, so a small change in climate shifts the boundary. For example, a rise in temperature can push the tree line in mountains upward, so monitoring ecotones gives early evidence of ecological change.

PYQ Practice — Statement Analysis

1 Ecotones usually have higher species diversity than adjoining ecosystems.

True

Called the edge effect.

2 A mangrove forest is a land and sea ecotone.

True

Rich in fish nurseries.

3 An ecocline is a sharp boundary between two communities.

False

It is a gradual gradient.

4 Edge species avoid ecotones.