Types of Symbiosis: Intimate relations among species 3-
Types of Symbiosis: Intimate relations among species
Commensalism is a type of symbiosis in which one member clearly benefits and the other apparently is neither benefited nor harmed.
Mutualism is a type of symbiosis in which both members clearly benefit.
A keystone species plays a critical role in a biological community
3.3 The Growth of Species Populations
Biotic potential— the amount of potential growth of a population with unrestrained biological reproduction.
Exponential (r) growth is population growth with no limits; it results in a “J” growth curve when graphed.
Logistic growth curves result from carrying capacity (K) limiting population growth; it results in a “S” shaped growth curve when graphed.
J curve of exponential growth 3-
Population cycles 3-
S curve of logistic growth 3-
Limits to population size
Density-dependent, meaning as population size increases, the effect intensifies. With a larger population, there is an increased risk that disease or parasites will spread, or that predators will be attracted to the area.
Density-independent limits to population are often nonbiological, capricious acts of nature. A population is affected no matter what its size.
Species respond to limits differently: r- and K-selected species 3-
Survivorship curves 3-
3.4 Properties of Communities Depend on Species Diversity
Diversity and abundance
Diversity is the number of different species per unit area.
Abundance refers to the number of individuals of a species in an area.
Species patterns create community structure
Boundaries of species populations and communities form patterns that fit together:
(1) individuals and species are spaced throughout communities in different ways;
(2) the communities themselves are arranged over a large geographic area or landscape
(3) communities have relatively uniform interiors (“cores”) and also “edges” that meet.
Community (or ecological) structure refers to these patterns of spatial distribution of individuals, species, and communities.
Individuals in communities are distributed in various ways
Random patterns arise from random distribution of resources.
Uniform patterns usually arise from competition.
Cluster patterns help a species protect themselves.
Communities are distributed in patterns across a landscape
Core habitat- a mostly uniform environment big enough to support nearly all the plants and animals that are typically found in that community.
Ecotone- or border between two communities, rich in species.
Edge effects- where communities meet, the environmental conditions blend and the species and microclimate of one community can penetrate the other. .
3.5 Communities Are Dynamic and Change Over Time
Climax community- The community that developed last and lasted the longest.
Primary succession- land that is bare of soil—a sandbar, mudslide, rock face, volcanic flow—is colonized by living organisms where none lived before.
Secondary succession -after a disturbance, if left undisturbed, a community will mature to a characteristic set of organisms.
Pioneer species -the first species to colonize a community in primary succession on land.
1. Explain how tolerance limits to environmental factors determine distribution of a highly specialized species such as the saguaro cactus.
2. Productivity, diversity, complexity, resilience, and structure are exhibited to some extent by all communities and ecosystems. Describe how these characteristics apply to the ecosystem in which you live.
3. Define selective pressure and describe one example that has
affected species where you live.
4. Define keystone species and explain their importance in community structure and function.
5. The most intense interactions often occur between individuals
of the same species. What concept discussed in this chapter
can be used to explain this phenomenon?
Practice Quiz continued
6. Explain how predators affect the adaptations of their prey.
7. Competition for a limited quantity of resources occurs in all
ecosystems. This competition can be interspecific or intraspecific.
Explain some of the ways an organism might deal with
these different types of competition.
8. Describe the process of succession that occurs after a forest
fire destroys an existing biological community. Why may
periodic fire be beneficial to a community?
9. Which world ecosystems are most productive in terms of biomass
( fig. 3.31 )? Which are least productive? What units are
used in this figure to quantify biomass accumulation?
10. Discuss the dangers posed to existing community members