5/17/16

1

Ecosystems

� Ecosystems are areas where the abiotic and biotic interact to form a community of populations

� May be large or micro � Each is individual in its

combination of factors

1

Biological Communities

� Community: all the organisms that live together in a specific place ●  Evolve together ●  Forage together ●  Compete ●  Cooperate

2

Biological Communities

� Interactions among members govern many ecological and evolutionary processes ●  Predation

●  Symbiosis 3

Biological Communities

� Two views of structure and functioning of communities ●  Individualistic concept: H.A. Gleason; a

community is nothing more than an aggregation of species that happen to occur together at one place

●  Holistic concept: F.E. Clements: a community is an integrated unit; superorganism-more than the sum of its parts

4

5/17/16

2

Biological Communities

Most ecologists today favor the individualistic concept

� In communities, species respond independently to changing environmental conditions

� Community composition changes gradually across landscapes

5

Biological Communities

� However, Lovejoy suggests that holistic explains earth’s history ●  Once O2 showed up in atmosphere, it

has remained at about the same concentration

●  Great extinctions are the result of the Earth resetting itself

6

Biological Communities

� Each line represents the abundance of a different tree species

� Community composition changes offer support for both views

Abundance of tree species along a moisture gradient in the Santa Catalina Mountains of Southeastern Arizona

7

Ecological Niche

� Niche: the total of all the ways an organism uses the resources of its environment ●  Space utilization ●  Food consumption ●  Temperature range ●  Appropriate conditions for mating ●  Requirements for moisture and more

8

5/17/16

3

Ecological Niche

� Niches within ecosystems are usually filled

� Organisms with the adaptations to overcome limiting factors survive to pass on the traits

9

When Niches Overlap

� Interspecific competition: occurs when two species attempt to use the same resource and there is not enough resource to satisfy both

� Interference competition: physical interactions over access to resources ●  Fighting ●  Defending a territory ●  Competitive exclusion: displacing an

individual from its range 10

Ecological Niche

� Fundamental niche: the entire niche that a species is capable of using, based on physiological tolerance limits and resource needs

� Realized niche: actual set of environmental conditions, presence or absence of other species, in which the species can establish a stable population

11

Ecological Niche

J.H. Connell’s classical study of barnacles 12

5/17/16

4

Ecological Niche

� Other causes of niche restriction ●  Predator absence or

presence � Plant species

●  Absence of pollinators ●  Presence of herbivores

Billock

Billock

13

Presence of Herbivores

14

Ecological Niche

Principle of competitive exclusion: if two species are competing for a limited resource, the species that uses the resource more efficiently will eventually eliminate the other locally

15

Ecological Niche

G.F. Gause’s classic experiment on competitive exclusion using three Paramecium species shows this principle in action

16

5/17/16

5

Ecological Niche

� Niche overlap and coexistence � Competitive exclusion redefined: no

two species can occupy the same niche indefinitely when resources are limiting

� Species may divide up the resources, this is called resource partitioning

� Gause found this occurring with two of his Paramecium

17

Resource Partitioning: Stratification

� Vertical layering of plants and animals ●  Plants must have adaptations for

differing amounts of light � Increases biodiversity by creating

micro-niches

18

Ecological Niche

Resource partitioning among sympatric lizard species

19

Resource Partitioning: Distribution

� 3 types ●  Regular, evenly placed (desert)

• Usually incorporates some type of growth inhibitor to stop competition

●  Clumped (common) ●  Random (rare)

20

5/17/16

6

Ecological Niche

� Resource partitioning is often seen in similar species that occupy the same geographic area

� Thought to result from the process of natural selection

� Character displacement: differences in morphology evident between sympatric species ●  May play a role in adaptive radiation

21

Ecological Niche

Character displacement in Darwin’s finches 22

Ecological Niche

� Detection of interspecific competition can be difficult ●  If resources not limited there may be

no competition ●  Small versus large population size ●  May be environmental conditions that

cause the decline of a species, not competition

23

Ecological Niche

Detecting interspecific competition 24

5/17/16

7

Ecosystem Evolution

� As time passes, organisms within the system have evolved characteristic traits for the system.

� Each ecosystem is fairly unique in its evolution due to: ●  Microclimates within ecosystem ●  Resource partitioning

25

Evolutionary patterns

� Two basic patterns of species evolution ●  Generalists ●  Specialists

26

Evolutionary Patterns

� Generalists ●  Can tolerate a wide range of

conditions ●  Seldom need any special condition to

survive ●  Niche is large and common ●  Utilize a r-style of reproduction

•  Produce a lot of offspring / little parental care 27

Evolutionary patterns

� Specialists ●  Usually has one narrow tolerance

range ●  Often needs a special condition to do

well ●  Often occupies a limited niche ●  Utilize a k-style of reproduction

•  Produce few offspring / a lot of parental care 28