Biology 2108 Lecture
Community - all populations in a specific area
Examples of questions in community ecology include: to what degree do populations 'behave' differently together then when alone; how do interactions maintain diversity; how important are these interactions in determining species composition of a community; and how stable are species assemblages over time?
Let's examine the first question: do populations 'behave' differently together then when alone?
Types of interactions between two populations (species)
- Mutualism - both species benefit
- Commensalism - one species benefits, the other neither benefits or is harmed
- Competition - both species are harmed
Species that share similar niches (the niche is the range of abiotic and biotic under which a species can live) are likely to be competing for a similar limiting resource. What can happen if two species living in the same community occupy very similar niches?
- Predation - one species benefits, the other is harmed
Are parasites predators? Are herbivores predators?
importance of predation is clearly demonstrated in the sophisticated
and prey adaptions. Co-evolution
is very intense in these
because improved adaptation of one species will directly affect other,
resulting in sophisticated adaptations.
For example, camouflage:
Is being the same color as the dominant background color necessarily the most adaptive coloration strategy?
The importance of community interactions:
Persistence of interactions (how interactions maintain diversity)
If population are not always stable and many interactions between populations are harmful, how do species persist over time (how is diversity maintained)?
Examples of competition and predation coexistence:
- Competitive networks
What happens if Species C is removed (goes extinct) from this community?
- Predator switching in communities with multiple species of prey
What happens if a predator diminishes the population of one prey species, and then what will happen to that prey population?
- "Key stone" predators limiting superior competitor
So, despite harmful interactions, the complexity of interactions can maintain diversity. Populations often evolve to take advantage of one another in an ecological 'arms race'.
All three of these examples lead to the seemingly paradoxical statement that biodiversity helps maintain biodiversity!
The importance of these interactions in maintaining diversity is demonstrated by success of exotic (invasive) species at the expense of native species.
What happens when humans introduce species into communities in which they have not evolved? Why do some species do better in environments in which they did not evolve than in they do in the environment in which they did evolve?For example, Rabbits in Australia
is also important in maintaining diversity
So, both species
interaction and phyiscal disturbances are important in maintaining
communities are dynamic (how species
composition changes over time)
The number of species may remain fairly constant over time.
For example, the number of species on an island is directly related to island size (as a result of an equilibrium between species extinction and immigration).
How might this be useful in predicting loss of biodiversity as a result of habitat destruction and fragmentation?
Bottom line: Species interact in numerous ways within communities and many of these interactions important in maintaining diversity. But non-equilibrium processes can also be important in positively influencing diversity, demonstrating that natural systems are dynamic.Changes in species composition of community over time are well documented:
Ecological Succession - a fairly predictable change in species compostion over time.
Typically, the series of community changes begins with a disturbance.
Examples of succession:
- U.S. Southeast Piedmont Region (e.g. the KSU Aboretum)
What drives ecological succession? How is the presence of later-succession species dependent upon early ones modifying the environment so that it is favorable to the later?
- Lakes and ponds
Lakes are at the bottom of their watersheds so that lakes accumulate the nutrients that runoff the watershed, causing drastic changes in lake ecosystems over time. Lakes change over time in a process know as eutrophication, typically going from clear lakes (few nutrients, so few nutrients) to turbid lakes (many nutrients resulting in thick blooms of phytoplankton and little or no oxygen in deeper waters).