DensityDependent Limiting Factors So what in the world

Density-Dependent Limiting Factors

So what in the world is a densitydependent limiting factor? ? �Density-dependent: something that depends on the amount of organisms in a unit area. (5 examples to follow)

Competition � Crowded populations mean the individuals have to compete for food, water, space, sunlight, or anything else necessary for survival and reproduction � Some may have enough to survive, but can’t raise offspring � Some may die of starvation � The more individuals in an area, the faster resources are used up � Could be between individuals of the same or different species

Predation � Predator-prey relationships tend to fluctuate (go up and down) � If there is a lot of prey, the predator can eat more, increasing the number of predators � If the prey decreases too much in population, there won’t be enough food for predators and so the population of predators decreases

Herbivory (Predation of Plants) �Plant and herbivore populations fluctuate just like the predator and prey populations

Parasitism and Disease � Parasites and disease causing organisms feed at the expense of the host � This can weaken or kill the host � The larger the population the easier it is for the parasite or disease to travel through hosts

Stress from Overcrowding �Some species will fight amongst each other if they are overcrowded �This fighting can cause stress leaving individuals susceptible to disease �In a few species, overcrowding can cause females to neglect or kill their own offspring

Density-Independent Limiting Factors

So what is it? �A factor that affects all populations in similar ways, no matter the population size or density �It includes things like: �Hurricanes �Droughts �Floods �Natural Disasters

Wait a second…is it really density dependent? � So what would happen after a drought? ◦ No water so species will compete for the water � WAIT A SECOND MR. BLAUVELT! YOU’VE TRICKED US!

�Sometimes a density independent factor can lead to a density dependent limiting factor like competition �What do you think? ?

Thinking back to logistic growth… � We said that something happens to stop populations from growing. � How do density-independent and dependent factors play into this?

Carrying Capacity � These limiting factors contribute to what is called carrying capacity � Defined as: the maximum number of individuals of a species an environment can support

On a graph…

Exit Ticket �On a sheet of paper, write a paragraph explaining whether or not you think that density independent factors should be considered separate from density dependent factors. �Explain your answer using information from today.