Species Interactions and Population Ecology

Community Ecology Involves the study of species interactions Distribution of species around the world is determined by: Species fundamental niche Ability to disperse in an area Interactions with other species Competition Predation Parasitism Mutualism Commensalism

Intra- Specific Competition 1. Intra-specific competition: occurs among members of the same species 2. There is a limit to the number of individuals that can survive in an area 3. Compete for: Living space Mates Food and water Beta is on left and alpha is on the right. Beta challenges alpha for position in wolf pack.

Inter - Specific Competition 1. Inter-specific competition: competition between two or more species for some limiting resource such as: food or nutrients, space, mates, nesting sites— anything for which demand is greater than supply one species is a better competitor, interspecific competition negatively influences the other species by reducing population sizes and/or growth rates 2. Importance: influences species evolution, the structuring of communities and the distributions of species

Competition Competition: struggle of individuals to obtain limiting resources Competitive exclusion: two species trying to utilize the same resources at the same time cannot co-exist.

Resource Partitioning Resource partitioning: two or more species divide a resource based on the differences in the species’ behavior or morphology

Predation Predation: the use of one species as a resource (prey) by another species (predator) Predators help keep prey populations healthy Co-evolutionary relationship Examples: True predators: hunt, kill, and consume prey Herbivores: consume plants as prey

Parasitism   Parasitism: One organism benefits (parasite), the other is harmed or hurt (host) Endoparasites Exoparasites Parasitoids: lay eggs inside of other organisms Nest (brood) parasitism

Mutualism   1. Mutualism: both species benefit from the relationship 2. Each species in the relationship assists the other to its own benefit 3. If the benefit is too small, it will no longer be worth the cost of helping the other species; natural selection would select against this relationship

Commensalism   Commensalism: one species benefits and the other is neither harmed nor helped Examples: Birds perching on tree branch Fish hiding from predators in coral reef

Population Ecology Population Ecology: Study the factors that cause populations to increase or decrease. When is it useful? Endangered species Cause of the decline? Situation improving? Invasive species How did it get here? How can we control growth? Pests How is the pest affecting humans and other organisms?

Density Dependent Limiting Factors Influence an individual’s probability to survive and reproduce Large populations are affects more than smaller populations Examples: Amount of available food Parasitism and disease Competition and predation

Density Independent Limiting Factors Affects all members of the population regardless of the size of the population or the health of the individuals Examples: Natural disasters (droughts, floods, hurricanes, tornados, wildfires, earthquakes) and pollution

Exponential Growth Model J shaped curve Population grows indefinitely as long as there is no environmental resistance Continuously increasing population; grows at a fixed rate

Logistic Growth Model S-shaped curve Population is initially exponential, but it slows as limits are placed on the population Limits include: Too little food Too much waste Disease

Carrying Capacity Carrying capacity: Referred to as K Maximum number of individuals the population can support at a given time Not fixed Overshoot: when population becomes larger than spring food supply; will then result in a die-off or population crash

Survivorship Curves Patterns of survival Type I: K-selected Have high survival rate throughout most of their life; die as they reach old age EX: elephants, humans, whales Type III: r-selected Low survivorship early in life; few individuals reach adulthood EX: salmon and mosquitoes Type II: EX: Rodents, birds, and corals Relative constant decline in survivorship throughout life

Predator-Prey Populations Populations of both species cycle over time. The lynx population peaks 1-2 years after the hare population peaks. As the hare population increases, it provides more food for the lynx population. Food becomes more scarce for the hare population, so their numbers fall. The lynx has less hares to eat, so its population fall.

Reproductive Strategies K-selected species: Low intrinsic growth rate; population increases slowly Traits: Long life span Long time to reach maturity Few reproductive events Few offspring produced per pregnancy Large offspring Parental care Population regulated by density dependent limiting factors Abundance is determined by carrying capacity (K)

Reproductive Strategies r-selected r stands for rapid Traits Short life span Short time to reproductive maturity Many reproductive events Many offspring at one time Offspring small size No parental care Fast population growth Population is regulated mainly by density independent limiting factors Population dynamics variable

Ecological Succession Ecological succession: the normal gradual change in species composition in a given area over time Number and types of species in an ecosystem change in response to changing environmental conditions Fires Volcanic eruptins Climate change Clearing forests

Primary Succession Begins with bare rock exposed by geologic activity - volcanism, glaciers, abandoned highway, newly created pond No soil Pioneer species: first to colonize previously disrupted or damaged ecosystems, beginning a chain of ecological succession

Secondary Succession Begins on soil from which previous community has been removed (by fire, flood, agriculture) Secondary succession can proceed much faster because the soil has been prepared by the previous community

Eco Succession & Biodiversity