Topic 2.6 CHANGES• K- strategists
• r-strategists
• Defined by amount of energy and time they invest in rearing their offspring
• Not all species fit perfectly into the two categories
Defined by amount of energy and time they invest in rearing their offspring
Which is the K or R Strategist and why?
K-strategists • Few offspring
• Most offspring survive
• Individuals take a long time to mature
• May reproduce several times during adult life
• Population size of K-strategist species is usually close to the carrying capacity
• K-strategists are usually predominant species in a stable ecosystem
• Can be vulnerable to extinction (ex. Polar bear )
K-strategists • Ex. Great apes (orangutans and gorillas), elephants
• Gorillas give birth at age 10
• Will care for baby for up to 6 years.
• Lifespan of gorilla up to 40yrs
K-strategists • Ex. Great apes (orangutans and gorillas), elephants
K-strategists • Ex. Great apes (orangutans and gorillas), elephants
r-strategists • Short lifespan
• Offspring mature quickly and are usually small
• Adults cannot invest time and energy in caring for such large numbers of young, so most offspring die
• b/c quick reproduction, they can colonize new environments easily and make use of short-lived resources
r-strategists • Ex. Insects such as spiders, fish and frogs and plant
species such as dandelions
Survivorship curves • Based on ability of individuals to reach reproductive
age.
• % of individuals that die before reproductive age affects pop. size
• Most organisms begin to age once they have past maturity. Strength declines and they die as they reach the natural life expectancy.
Line 1: K-strategists • When members of species are young
–Mortality is low b/c offspring cared for by parents
• Most individuals reach reproductive age
• Most individuals achieve expected lifespan
• Ex. Humans, big cats, eagles
Line 3: r-strategists • When members of species are young
–Mortality is high
• Individuals that survive are likely to live for expected lifespan
• Ex. Most invertebrates and plants, frogs, organisms with free-swimming juvenile stages like barnacles
Line 3: r-strategists
Line 3: r-strategists
Line 2: intermediate organism • Equal likelihood of dying at any age.
• Death could be due to factors such as hunting, diseases or chance
• Examples: mice, coral, and many reptiles
Succession
Defined by amount of energy and time they invest in rearing their offspring
Which is the K or R Strategist and why?
The Process of Succession
• Succession is the long term ecological process by which communities in a particular area change over a period of time
• Involves interactions between biotic and abiotic components
–Pioneer (early) communities modify the physical env. which in turn modify the biotic.
– This allows more species to move in and modify physical env. still more
–Continues until stable situation is reached
Primary Succession
Primary succession
• An area of bare ground is colonized for the first time.
• Examples:
– Surtsey a newly formed volcanic island of the coast of Iceland which formed in 1963
Erupted to life in 1963 Stooped erupting in 1967
1982 It was not unexpected that free- living blue-green algae with the ability to use sun energy and the molecular nitrogen of the air for growth and development, were among the primary immigrants of Surtsey.
2004 60 plant species growing on the island 89 species of birds 335 species of invertebrates
• Examples continued:
• Glacial melt
• Examples continued:
• Catastrophic Events that remove soil are also considered primary succession
Mt. St. Helen’s Pre eruption. 1979
Mt. St. Helen’s after eruption. 1981
One of the first plants to reappear, appropriately enough, was the fireweed (pictured above). The presence of plant life enticed deer and elk to return to the area. With their wanderings, they stirred up even more ash, freeing seeds and shoots of plants still buried. Even though there were over 1500 elk killed as a result of the eruption, the elk population had returned threefold by the early 1990’s thanks to mild winters, an abundance of food on the debris avalanche, and the lack of human interference.
Low shrubs are growing in 5–10 years
2014
• After an area of previously established land has been cleared:
• Could be from: Forest fire, flood, landslide, or tsunami
• Soil already present so succession can occur more rapidly than primary succession.
Changes Occurring During Succession
• Size of organisms increases with trees creating more hospitable environment
• Energy flow becomes more complex as simple food chains become more complex
• Soil, humus, water holding capacity, mineral content and cycling all increase
• Biodiversity
increases because of more niches appear
Energy Flow and Productivity at different stages of succession • As succession develops productivity of the system also
changes.
– Few producers present
– Gross productivity is low but energy lost in respiration by these organisms is also low
– This means that net productivity is high because the ecosystem is growing and accumulating biomass.
Energy Flow and Productivity at different stages of succession • As succession progresses
• more consumers are present and gross productivity may be high.
• With more consumers there are more complex feeding interactions and food webs so net productivity also increases.
• GPP and NPP stabilizes as a climax community is reached
Energy Flow and Productivity at different stages of succession • As succession develops, productivity of the system
also changes.
(P:R ratio)
If P : R > 1 biomass accumulates
If P : R < 1 biomass is lost
During succession, the following changes occur:
• Size of organisms increases, trees create more hospitable env.
• Energy flow becomes more complex (food chains become food webs)
• Increase of soil depth, humus, water-holding capacity, mineral content and cycling
• Biodiversity increases (more niches), then falls (climax community reached)
• NPP and GPP rise, then fall
• P:R ratio falls
• Gross productivity is low
• but energy lost from community respiration is low (few, if any, consumers and decomposers)
• This means that net productivity is high
• because the ecosystem is growing and accumulating biomass.
• P:R > 1
community
• Gross productivity is high
• But, it is balanced by equally high rates of respiration (especially by decomposers)
• So, net productivity falls
• Succession leads to a maximum accumulation of biomass.
• Upper limit of biomass is reached when respiration losses (R) from a system almost equal GPP.
• When this happens, NPP will equal 0
NPP = GPP – R
Factors affecting climax communities • Stable ecosystems are regulated by feedback
mechanisms which enable the system to rebalance itself if changes occur.
• As climax communities are reached:
– food webs become more complex
– Interactions between diverse species ensures consumers can use alternative food sources
–Plants have good reservoir of nutrients and organic matter are not dependent on inputs from outside the system
Factors affecting climax communities • The exact nature of a climax community is
determined by climatic and edaphic factors (the physical, chemical and biological properties of soil ex: water content, organic content, texture, and pH)
• Climax communities have been reached when:
–Has higher biomass
– Larger species diversities
– Larger longer lived species with a greater proportion of K-strategists
–Greater habitat diversity
Human interference in climax communities • Humans can interfere/ interrupt natural succession
–Clear land for agriculture
Natural events like fires and landslides can also interrupt succession
Human interference in climax communities
–After an interruption the climax community which results will be different from the naturally occurring one
– This is said to be a deflected succession and has given rise to a plagioclimax (a climax community that has replaced the naturally occurring community as a result of human activity)
Examples
Rainforest clearing:
–Cleared land may be planted with crops that leach out the nutrients of the soil preventing that area from reaching a new climax community.
– Each year it is estimated that the size of a small country is cleared.
Examples
Prairies:
–America prairies are a plagioclimax
–Over many years fire and human use have left grasses in place of trees
– This limits tree growth so succession does not continue
Examples
Moorland:
–United Kingdom has large areas of moorland they are a plagioclimax
–People cut down trees for fuel usage
–Grazing animals eat plants preventing plant development
Disturbances
• Communities are effected by disturbances to a greater or lesser extent
• Natural disasters or human influence can cause a disturbance
• These have an effect of making gaps available that can be colonized by pioneer species
• This adds to the productivity and diversity of the community
Zonation • For each species there is an ecological niche
• That niche has boundary limits and outside of these the species can not live
• Examples: