1. CHAPTER 5 Factors That Limit Distribution & Abundance: BIOTIC COMPONENTS

2. Learning Outcome Define biotic factors
Acquire knowledge on the interrelationship between organism
Describe the criteria proposed for predator to restrict its prey
Explain resource partitioning

3. What is biotic factors?
Biotic factors are factors produced by living organisms that affect the ability of other living organisms to survive in an environment.
Example: disease, parasitism, predation, allelopathy and competition.

4. PREDATION 1)PREDATOR RESTRICT PREY
Works by Kitching & Ebling (1967) – studies in Ireland on the mussel (Mytilus edulis).
Exposed rocky shores = small mussels
Sheltered area = larger mussels
Kitching transferred rock with attached mussels from one area to another

5. Results
Small mussels transplanted to/within the are – survived only on open coasts while in other areas they disappeared-because of the influence of predators.
Large mussels only survived in their natural habitat but disappeared in transplanted areas

6. How predator restrict its prey?

7. Example 2
Kitching & Ebling (1961) – relationship between sea urchin, Paracentrotus lividus and algae.

8. The predator (sea urchin) lives in the shallow part of the sublittoral zone (under beach) – just below the tide level.
In areas where there is abundant sea urchins the area is relatively free of algae
In areas where there is little sea urchin the algae are abundant

9. They did experiments of clearing 1957 sea urchins (290 m2)
- Algae immediately began to colonize and grow in the sea urchin cleared area.
In adjacent areas where there were sea urchin, algae cover was not visible.

10. The authors then transferred the sea urchin into areas that had high growth of algae – the areas began to be clear of algae.
There was thus a reverse relationship between sea urchin and algae cover

11. Example 3
Small kangaroos a.k.a rock wallabies (prey) have been driven to extinction by:
1. Predation of introduced sp. i.e, the red fox (predator).
2. Competition for food with rabbits.
Habitat: Rocky hills
Declining and numerous colonies have become extinct

12. Kinnear et al. (1998) tested the hypothesis that red fox predation was sufficient to limit the population and size distribution of rock wallabies
Test: They poisoned red foxes around experimental colonies at rocky hills
Result:
1. it showed that the populations of wallabies recovered (in absence of red fox)
2. Without foxes, wallabies ranged further from rocky sites to feed – better species distribution.

13. Example 4 – Rat Kangaroo Previously found extensively over Australia.
Presently only found at 3 islands off the coast of Western Australia where there are no red foxes.
Reintroduced to mainland, isolated by electric fence to prevent fox immigration and poisons to eliminate foxes.
Reintroduction was a success.

14. 4 criteria for predator to restrict its prey:
Suspected predator is able to kill prey in lab (experiment) and field (nature)
Suspected predator is responsible for destruction of prey in transplantation experiments
prey survives after transplanted if they are protected from predators
prey distribution and suspected predator are inversely related

15. PREDATION 2) PREY RESTRICT PREDATOR
- plant (food) vs herbivore (insect)
- herbivore vs carnivore
- Such predators are called specialists or monophagous predators

16. Example 1
Chrysolina quadrigemina introduced in US to control the Kalmath weed, Hypericum perforatum.
Adults and larvae of beetle will only feed on the Hypericum or they will die if feed on other plants
Adult beetles display an obligatory feeding response to the chemical hypericin (Schoeps et al., 1996)
The beetles refuse to stand on other leaves that have different surface feature to that of Hypericum
The life history, feeding habits, behavior and distribution of the beetle (predator) is restricted by its single plant (prey)
Restricted to one mode of life

17. Insects that feed on only one host plant (monophagous insects) could be limited in their distribution by the host plant.
To date there is no indication that the ranges of food plants and their monophagous insect herbivore coincide (Quinn et al., 1998)
Example of the butterfly in Britain – no association between food plant distribution and butterfly distribution
Even for widespread species of butterflies the host plant occurs in many areas in which the butterfly does not – something else must limit butterfly distribution

18. Disease & Parasitism

19. Disease & Parasitism
Parasites and pathogens can limit and restrict distributions
Example - native bird fauna of Hawaii
Native birds of Hawaii have become extinct due to introduced disease – (Warner, 1968):
1. avian pox (initially) and 2. avian malaria (later) were instrumental in causing extinction in the Hawaiian Islands
Bill tumors results of avian pox

20. The idea that disease might be involved arose from observations that:
native birds occupy upperland in Hawaii and are relatively common only at elevation above 1500 m
while introduced birds occupy lowland

21. Female Culex quinquefasciatus
The malarial vector, Culex quinquefasciatus is conversely most common in lowland areas
Male Culex quinquefasciatus

22. The initial extinction of native birds was initially influenced by habitat clearing for agriculture and introduction of rats, cats, and pigs and avian pox (before 1900) and subsequent extinction by introduction of avian malaria.
Birds that went extinct at this time (early 1900) lived in the mid-elevation forests where malaria parasites are most common.

23. Allelopathy

24. Allelopathy
Definition: The inhibition of growth and development in one species of plants by chemicals produced from another species. Plant vs plant.
Impact :
- Decrease in yields - did not increase even after adding of fertilizers.
- E.g Grass and apple trees
- Experiment: Apple trees supplied with 3 different sources of water:
a primary source: tap water
a secondary source: water passing through grass and soil
water that passed through soil only
The growth of apple seedling was inhibited by something produced by the grass and carried by water.
Soil sickness- soil microorganisms and plants are important in allelopathy. Fungi and bacteria may produce and release inhibitors or promoters. Some bacteria enhance plant growth through fixing nitrogen, others through providing phosphorus. The activity of nitrogen-fixing bacteria may be affected by allelochemicals, and this effect in turn may influence ecological patterns.

26. alfalfa plants
Example 2
Effect of black walnut trees (Juglans nigra) on grass and alfalfa plants.
Roots secrete a toxin to which tomatoes and alfalfa could not grow but others like corn and beet showed no ill effect
The chemical is juglone, 5 –hydroxy-α-napthaquinone) from roots and hulls of black wallnut.
Some close relatives of black walnut (Juglans regia, J. bindsii, J. califronica) do not produce toxins
Inhibitor of seed germination
Tomatoes and alfalfa wilt when grown near black walnuts, and their seedlings die if their roots contact walnut roots.
A chemical compound in the leaves and green stems of the black walnut tree is leached by rainfall into the soil. The chemical compound from the black walnut tree leached by rainfall into the soil is hydrolyzed and oxidized into another compound called juglone. Juglone has been shown to be very toxic to many plants as well as an inhibitor of seed germination. Tomatoes and alfalfa wilt when grown near black walnuts and their seedlings will die if their roots contact walnut roots. Similarly, white pine (Pinus strobus) and black locust (Robinia pseudoacacia) are often killed by black walnuts growing in their vicinity
Juglans nigra

27. Presence of other organisms may limit distribution of some species through competition.
Allelopathy is one specific type of competition for living space.
Allelopathy vs competition.

28. Competition

29. Competition happen when 2 or more species uses the same resources and live in the same places.
Birds, rodents and ants may compete for seeds in desert environments.
Herbs and shrubs compete for water in dry areas.
Competition among animals is usually for food, mate, habitat.
Plants compete for sunlight, nutrients, water, even pollinators

30. How do we know if competition is restricting geographic distribution?
– when sp A is absent, sp. B lives in a wider range of habitats.
In some extreme cases a habitat will contain only sp A or B and never both.
The difficulty is that competition is only one of the several hypotheses that can account for the observed distributions.

31. Example 1, Checkerbord distribution
Checkerboard distribution of closely related sp – ecologically related sp. in an island archipelago – interdigitating distributions (become interlocked)– each island supporting only 1 sp.
The fruit pigeon in the Bismarck Archipelago – Ptilinopus rivoli and P. solomonensis.
The successful colonist is either first-come-first basis or on the basis of slight competitive advantage.
Alternately arranged

33. Resource partitioning
When 2 sp compete for resources:
one will always be a better competitor and the other will lose out and disappear.
evolves together, adapt to
escape/ minimize competition
2 evolutionary strategies a weaker competitor species can develop:
avoid the superior competitor by selecting different part of the habitat (E. umbrinus –arboreal)
avoid the superior competitor by selecting a different diet (diet shift)
Resource partitioning

34. Example 2
Competition among cliff chipmunks – Eutamias dorsalis, E. umbrinus
E. dorsalis (lower elevation) excludes E. umbrinus (higher elevation)
The 2 sp interact at about 2100 m where the levels of competition are highest.
Eutamias dorsalis
Eutamias umbrinus

35. Habitat structure E. dorsalis
- lower elevation prefers lives on the ground, less trees
- aggressive to its own and other chipmunk sp.
E. umbrinus
- higher elevation
- lots of trees
- spends its time on trees
- moves from tree to tree along interlocking branches

36. At lower elevation where trees are sparse, E. dorsalis exludes E
At lower elevation where trees are sparse, E. dorsalis exludes E. umbrinus by its superior aggression.
Aggression become ineffective when tress are close (dense) spaced because the arboreal umbrinus escapes through the trees.
Competitive success of E. umbrinus is determined by habitat structure.

37. Example 3
Crossbill finches – extract seeds from cones – 3 sp live in Eurasia and are adapted for eating different foods
i) Small crossbill – (Loxia leucoptera) – small bill feeds on larch seeds – cones are soft
ii) Medium sized crossbill (L. curvitrostra) – eats spruce seeds
iii) Large crossbill (L. pytyopsittacus) eats the hard cones of Scotch pines.
This minimizes dietary overlap in regions where all three possible competitors live.
Loxia leucoptera
Loxia pytyopsittacus