Population Dynamics at Rhyd y creuau

Size: px

Start display at page:

Download "Population Dynamics at Rhyd y creuau"

Flora Stevenson
6 years ago
Views:

Population Dynamics of the Holly Leaf Miner (Phytomyza ilicis) Aims Objectives: To describe the mortality within a generation of the holly leaf miner insect To determine factors that could regulate,

1 Population Dynamics of the Holly Leaf Miner (Phytomyza ilicis) Aims Objectives: To describe the mortality within a generation of the holly leaf miner insect To determine factors that could regulate, or cause changes in, population size This study will allow us to: Population Dynamics at Rhyd y creuau Use microscopes and dissection tools for the collection of ecological data Cover some of the ecological terminology and concepts needed for the study of population dynamics df Your Objective:.... Tick when achieved Concept s we ll be covering: Before After Population growth (lag time and exponential growth) Density dependent limiting factors Density independent limiting factors Carrying capacity Predator-prey relationships Pest control (chemical, biological and integrated pest management) Introduction: The holly leaf miner (Phytomyza ilicis) is a species of insect whose life cycle revolves around holly (Ilex aquifolium). Adult holly leaf miners, which resemble small house flies, lay their eggs on holly leaves. When the eggs hatch, the maggot-like larvae feeds on the leaf s tissue, creating a distinctive blotch mine. As most of the insect s life cycle takes place within holly leaves, mortality factors can be identified and quantified. Population dynamics: Starting from a population of two holly leaf miners, if all mortality factors were removed, how many would you have in 3 years? What percentage mortality is required to keep the population at a constant level? Population after 3 years: Required % mortality:

Life cycle of the Holly Leaf Miner (Phytomyza ilicis): 1. During late May to June the adult fly emerges from a pupa within the mine through the leaf, creating a small exit hole 2.

2 Life cycle of the Holly Leaf Miner (Phytomyza ilicis): 1. During late May to June the adult fly emerges from a pupa within the mine through the leaf, creating a small exit hole 2. The adult fly, which resembles a tiny house fly, mates. A single egg is laid on each holly leaf, into the base of the underside of the midrib Spring: s may attack the larva or pupa of the miner. The parasite larva is yellow and the parasite pupa or pupal skin is shining black. The adult parasite emerges from within the mine creating a minute exit hole Life Cycle of the Holly Leaf Miner Autumn: Disease may kill young larvae, in which case the mine is small and contains black and white grot 3. The holly leaf miner pupates inside the leaf in March, after preparing a small patch in the surface of the mine. The pupa is light brown Winter: Predators (blue tits) may tear open the mine and feed on larva, leaving a characteristic v-shaped tear 4. After hatching, the larvae eat through the midrib and enter the outer parenchyma of the leaf during the autumn The larva continues to feed throughout the winter months, creating distinctive blotch mines

3 Data Collation Population Dynamics of the Holly Leaf Miner Eggs don t hatch (D1) Key: No. of mines eggs (N0) No. of mines (N1) Larval disease (D2) N = Number of surviving individuals ESTIMATE D = Mortality factor Death of adults (D7) No. of mines (N7) ESTIMATE No. of mines (N2) Larval parasite (D3) No. of mines (N6) No. of mines (N3) Calculations: Pupal failure (D6) No. of mines (N5) No. of mines (N4) Predation by birds (D4) Overall percentage mortality: N1 N6 = x 100 N1 Pupal parasites (D5) =...%

4 Who Killed the Holly Leaf Miner? Emergence hole c0.5mm. Dissection reveals black pupal skin of parasite) but no puparium killed larva d3 = Emergence hole c0.5mm. Mine contains brown puparium (of leaf miner) with black pupal skin (of parasite) inside killed pupa d5 = Large emergence hole (>1mm). Dissection reveals shiny light brown puparium left by emerging leaf miner Successful leaf miner V shaped tear indicating peck mark present. No remains of leaf miner present inside mine Predation by blue tit d4 = START HERE Tear or hole present in the surface of mine (check lower and upper epidermis Dissection reveals shiny light brown puparium of leaf miner Dissection reveals dull and dark brown puparium Puparium of leaf miner contains black pupa of parasite Puparium of leaf miner does not contain black pupa of parasite Healthy pupa of leaf miner killed pupa Other death of pupa d5 = d6 = Dissection reveals living larva shiny and lemon yellow in colour Healthy larva of leaf miner miner with black pupa of parasite lying near to remains miner. Remains appear flaccid and dirty yellow in colour killed larva d3 = Dissection reveals no conspicuous remains of larva at all miner. Remains appear shrivelled and greenish in colour Other death of larva d2 =

5 Population Regulation and Dynamics Discussion Although population explosions or extinctions may grab the news, in reality most populations of organisms in stable ecosystems remain remarkably constant over time. What causes this regulation of populations has vexed ecologists for almost a century and much on this subject remains to be learnt. Mortality factors: Mortality factors are factors which prevent populations from increasing rapidly in number: Density Factors Density Factors Disease Predation Fire Frosts These two types of mortality factors act on populations in different ways. Very generally, these factors combine to give the following growth curve: What type of growth curve is this? Pop. Size K = Time Stage Name Description 1 A small population colonizes an area where space and food are plentiful. The population slowly establishes itself. 2 Exponential growth occurs. 3 Growth slows due to the constraints of the environment (these constraints are called limiting factors). 4 The population size stabilises around the environment s carrying capacity (k) for that population. The carrying capacity is the average number of a population the area can hold. Oscillations around the carrying capacity are generally caused by seasonal or climatic factors. Think: Why is it important to study population dynamics?

ACTIVITY 1 What happened to the holly leaf-miner?

ACTIVITY 1 What happened to the holly leaf-miner? ACTIVITY 1 Introduction Holly trees (Ilex aquifolium) are common in city squares and urban parks, and several are found in Gordon Square. In this investigation, pupils collect evidence of the food chain