A population is a group of individuals of the same species living in the same area. We study population growth patterns and survival statistics.
Basic Knowledge
Methods for investigating population density: quadrat method(effective for plants and similar organisms) and mark-and-recapture method=N = n₁ × n₂ / m (N=total population, n₁=number initially captured, n₂=number recaptured, m=number of marked individuals among the recaptured individuals).
Population growth curves: J-shaped growth(exponential increase・without environmental resistance) and S-shaped growth(logistic growth)=approaches the carrying capacity(K) because of limitations on food・space. Equation: dN/dt = rN(K-N)/K. The rate of increase is greatest when N=K/2.
Three types of survival curves: convex(Type I)=high survival rate until old age・rapid death at the end(humans・large mammals). Linear(Type II)=a constant proportion dies at each age(birds). Concave(Type III)=high mortality during early life・long life if it survives(fish・invertebrates).
In a mark-and-recapture study, 50 individuals were first captured, marked, and released. The next day, 40 individuals were recaptured, of which 8 were marked. Estimate the population size of the pond.
Answer: N = n₁ × n₂ / m = 50 × 40 / 8 = 250 individuals.
- Mark-and-recapture method: N = n₁ × n₂ / m
- J-shaped growth=without environmental resistance・exponential increase
- S-shaped growth=approaches carrying capacity K・rate of increase is greatest at N=K/2
- Convex(Type I)=humans・large mammals
- Linear(Type II)=birds
- Concave(Type III)=fish・invertebrates(high mortality during early life)
- Life table=statistics of survival・death・reproduction in a cohort
Points to Note
① The mark-and-recapture method assumes that individuals mix uniformly and that marking does not affect survival rate or capture rate. ② In S-shaped growth, the rate of increase is greatest at K/2. ③ Survival curves often use a logarithmic scale on the vertical axis.
Practice
- State what quantity each symbol in N = n₁ × n₂ / m represents in the mark-and-recapture method.
- What type of population growth curve occurs when food and space are not limited?
- What type of survival curve describes organisms with high mortality during early life that live long if they survive?