| 1. | an increase in number |
| 2. | a decrease in number |
| 3. | no change in number |
| 4. | an unpredictable change – may be an increase or may be a decrease – in number |
| I: | Natality |
| II: | Mortality |
| III: | Emigration |
| IV: | Immigration |
| I: | When resources in a habitat are unlimited, populations undergo exponential growth. |
| II: | Resources are always unlimited for plants but never for animals. |
| 1. | Mutualism | 2. | Commensalism |
| 3. | Parasitism | 4. | Competition |
| I: | In ecology, the term “niche” describes the role an organism plays in a community. |
| II: | A species’ niche encompasses both the physical and environmental conditions it requires and the interactions it has with other species. |