The logistic population growth model
`(dN)/(dt)=rN((K-N)/K)` describes a population
growth when an upper limit to growth is assumed. This upper limit of growth is known as population …….A……..and as N gets larger, `(dN)/(dt)` ……..B…….

Options

A. A-carrying capacity ,B-decrease
B. A-carrying capcity ,B-increase
C. A-reproductive fitness, B-increase
D. A-reproductive fitness ,B-decreases

Answer

To solve the question regarding the logistic population growth model, we will break it down into two parts: identifying the term for the upper limit of growth and understanding the behavior of the growth rate as the population size increases.

### Step-by-Step Solution:

1. **Understanding the Logistic Growth Model**:
The logistic population growth model is represented by the equation:
\[ \frac{dN}{dt} = rN\left(\frac{K-N}{K}\right) \]
Here, \(N\) is the population size, \(r\) is the intrinsic rate of natural increase, and \(K\) is the carrying capacity of the environment.

2. **Identifying the Upper Limit of Growth**:
In the context of logistic growth, the upper limit to population growth is referred to as the **carrying capacity**. This is the maximum population size that the environment can sustain indefinitely. Therefore, for blank A, the answer is:
\[ \text{A: carrying capacity} \]

3. **Analyzing the Growth Rate as Population Size Increases**:
As the population size \(N\) approaches the carrying capacity \(K\), the term \((K-N)\) in the equation becomes smaller. This leads to a decrease in the growth rate \(\frac{dN}{dt}\). Specifically, when \(N\) is equal to \(K\), the growth rate becomes zero, indicating that the population has reached its maximum sustainable size. Thus, for blank B, the answer is:
\[ \text{B: decreases} \]

### Final Answers:
- A: carrying capacity
- B: decreases