Athletes train for years to compete against the best of the best at the Olympic games. Each athlete uses a large amount of resources to compete, including time, energy, and money. Only one athlete wins each event in the end. However, competition encourages all athletes to build on their strengths and reduce their weaknesses over time. Competition for limited resources among populations also involves costs and benefits. 15. Discuss Working with a partner, brainstorm a list of resources that populations might compete for in an ecosystem. Choose one resource from your list to consider further. What evidence might you gather to determine whether two populations compete for this resource?

Populations in an ecosystem might compete for a variety of resources, including: • Water • Nutrients (like nitrogen or phosphorus) • Light (for photosynthesizing plants) • Food (prey or specific foraged items) • Shelter or nesting sites • Territory or space • Pollinators (in the case of flowering plants) Let’s choose water as an example to explore further. To determine whether two populations (for instance, two species of amphibians or plants) are competing for water, you could gather the following evidence: 1. Overlapping Distribution and Habitat Use:  • Map where each population is found and see if they coexist in areas with similar water availability.  • Notice if one group tends to occur in drier microhabitats, suggesting they might be pushed to a less optimal zone if competition exists. 2. Resource Availability Measurements:  • Measure water levels in habitats where the populations overlap versus where they occur separately.  • Determine whether water levels decline particularly in areas where both populations are present, which could indicate intense use and competition. 3. Behavioral and Physiological Observations:  • Look for behavior that indicates competitive interactions (e.g., aggressive encounters around water sources, displays of territoriality during dry conditions).  • Check for adaptations or stress responses related to water scarcity, such as dehydration indicators or altered foraging behavior. 4. Population Dynamics Data:  • Monitor population sizes over time in relation to periods of water scarcity versus abundance. If numbers decline particularly when water is limited, and especially if one population suffers more in shared habitats, it may signal competition.  • Analyze reproduction or growth rates. For example, if one species produces fewer offspring during droughts in areas where both species co-occur, water competition might be a contributing factor. 5. Experimental Manipulations:  • Set up controlled experiments, if possible, where water availability is manipulated. Compare growth, survival, or reproductive success of each population in environments with varying water amounts.  • Observe if removing or adding water alters the relationship or competitive outcomes between the populations. 6. Resource Use Efficiency Studies:  • Examine how efficiently each population uses water. If one species is able to extract moisture more effectively (via root structure in plants or behavior in animals), it might competitively exclude the other during times of water shortage. By collecting and synthesizing these types of evidence, you can build a strong case for whether the two populations are indeed competing for water, or whether they might instead be partitioning the resource in some way (for example, by using water at different times or in slightly different areas). This approach can be adapted to studying competition over other resources by focusing on similar types of evidence relevant to that resource.