A few individuals of a bird species fly to a small city that previously had no individuals of this species. The immigrant birds find that the city has adequate food and no predators. On average, each bird has four offspring per year and lives for two years. Imagine that after the birds have been living in the city for many years a second big flock of birds arrives. How will the bird population size change in the 10 to 20 years after the extra birds arrive?

There are several factors that affects the population of a species in an area such as environmental conditions, number of predators and availability of food.

When first species of arrives  in the city, city has adequate food and no predators, then the population of birds has increased for few years before arrival of the second flock of birds.n But after the arrival of second flock of birds after many years (might be 10 to 20 years) the population of first species of birds will decrease because now competition for food has increased and both the species will compete for same food present in the city. Extra birds arrival in the city will increase the competition among both species birds for food and the fittest bird will be able to survive.

Hence, the population size of birds (first flock) will decrease in the 10 to 20 years after the extra birds arrive.

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